Introduction
The introduction of automation, whether incremental or comprehensive, involves some interference with an ongoing process that cannot be disrupted. Consequently, careful planning is required so that the transition can be made with minimal interruption. Despite the FAA's past efforts to foster greater human factors involvement in the development and implementation of advanced air traffic control systems, the agency's success record has been mixed at best.
However, a recently completed, independent study (by the Human Factors Subcommittee of the FAA's Research, Engineering, and Development Advisory Council) examined the current FAA organizational structure, staffing, and operating practices as they relate to human factors support activities, making recommendations for improving the effectiveness of this function. These recommendations appear to be well founded and offer the potential for better integration of human factors activities in the development of advanced automation technologies.
The panel recommends that senior Federal Aviation Administration management should reexamine the results of the study by the Human Factors Subcommittee of the FAA's Research, Engineering, and Development Advisory Council, with a view toward implementing those recommendations that appear most likely to achieve more active, continued, and effective involvement of both users and trained human factors practitioners in the development and implementation of advanced air traffic control systems.
All aspects of human-centered automation should be considered in fielding new automated systems. The Federal Aviation Administration should continue to support integrated product teams with well-trained human factors specialists assigned to the teams. Both users and human factors specialists should be involved at the early stages to help define the functionality of the proposed automation system.
These specialists should be responsible to report to human factors management within the Federal Aviation Administration as well as to project managers.
The Federal Aviation Administration should continue to work toward an infrastructure in which some human factors training is provided to personnel and program managers at all levels of the organization (and contract teams).
The Federal Aviation Administration should ensure that adequate funding is provided for needed human factors work at all stages of system development and field evaluations both before and after systems acquisition. During the development of each automation function, system developers should consider possible interactions with other automation functions (under development or already existing), tools, and task requirements that form (or will form) the operational context into which the specific automation feature will be introduced.
AUTOMATION ISSUES AND EMERGING TECHNOLOGIES
This book provides a rationale, based on a human factors perspective, for making decisions about (1) the extent to which automation should be applied to the performance of national airspace system functions and (2) the issues to consider and the methods to apply during design and introduction of systems that incorporate automation to maximize the safety, efficiency, usability, and acceptance of systems that incorporate automation.
The discussion and analysis is divided into three parts: Part I introduces definitions, concepts, and promising emerging technologies; Part II analyzes key automation initiatives; and Part III discusses research and development for the national airspace and presents conclusions and recommendations.
AUTOMATION ISSUES IN AIR TRAFFIC MANAGEMENT
The pressures for automation of the air traffic control system originate from three primary sources: the needs for improved safety, and efficiency (which may include flexibility, potential cost savings, and reductions in staffing); the availability of the technology; and the desire to support the controller. Even given the current very low accident rate in commercial and private aviation, the need remains to strive for even greater safety levels: this is a clearly articulated implication of the ''zero accident" philosophy of the Federal Aviation Administration (FAA) and of current research programs of the National Aeronautics and Space Administration (NASA). Naturally, solutions for improved air traffic safety do not need to be found only in automation; changing procedures, improving training and selection of staff, and introducing technological modernization programs that do not involve automation per se, may be alternative ways of approaching the goal.
The need for improvement is perhaps more strongly driven by the desire to improve efficiency without sacrificing current levels of safety. Efficiency pressures are particularly strong from the commercial air carriers, which operate with very thin profit margins, and for which relatively short delays can translate into very large financial losses. For them it is desirable to substantially increase the existing capacity of the airspace (including its runways) and to minimize disruptions that can be caused by poor weather, inadequate air traffic control equipment, and inefficient air routes. The forecast for the increasing traffic demands over the next several decades exacerbates these pressures.
Of course, as with safety, so with efficiency: advanced air traffic control automation is not the only solution. In particular, the concept of free flight (RTCA,1 1995a, 1995b; Planzer and Jenny, 1995) is a solution that allocates greater responsibility for flight path choice and traffic separation to pilots (i.e., between human elements), rather than necessarily allocating more responsibility to automation. Automation is viewed as a viable alternative solution to solve the demands for increased efficiency. Furthermore, it should be noted that free flight does depend to some extent on advanced automation and also that, from the controller's point of view, the perceived loss of authority whether it is lost to pilots (via free flight) or to automation, may have equivalent human factors implications for design of the controller's workstation.
It is, of course, the case that automation is made possible by the existence of technology. It is also true that, in some domains, automation is driven by the availability of technology; the thinking is, "the automated tools are developed, so they should be used." Developments in sensor technology and artificial intelligence have enabled computers to become better sensors and pattern recognizers, as well as better decision makers, optimizers, and problem solvers.
The extent to which computer skills reach or exceed human capabilities in these endeavors is subject to debate and is certainly quite dependent on context. However, we reject the position that the availability of computer technology should be a reason for automation in and of itself. It should be considered only if such technology has the capability of supporting legitimate system or human operator needs.
Automation has the capability both to compensate for human vulnerabilities and to better support and exploit human strengths. In the Phase I report, we noted controller vulnerabilities (typical of the vulnerabilities of skilled operators in other systems) in the following areas:
Monitoring for and detection of unexpected low-frequency events, Expectancy-driven perceptual processing, Extrapolation of complex four-dimensional trajectories, and Use of working memory to either carry out complex cognitive problem solving or to temporarily retain information. In contrast to these vulnerabilities, when controllers are provided with accurate and enduring (i.e., visual rather than auditory) information, they can be very effective at solving problems, and if such problem solving demands creativity or access to knowledge from more distantly related domains, their problem-solving ability can clearly exceed that of automation. Furthermore, to the extent that accurate and enduring information is shared among multiple operators (i.e., other controllers, dispatchers, and pilots), their collaborative skills in problem solving and negotiation represent important human strengths to be preserved. In many respects, the automated capabilities of data storage, presentation, and communications can facilitate these strengths.
As we discuss further in the following pages, current system needs and the availability of some technology provide adequate justification to continue the development and implementation of some forms of air traffic control automation. But we strongly argue that this continuation should be driven by the philosophy of human-centered automation, which we characterize as follows: The choice of what to automate should be guided by the need to compensate for human vulnerabilities and to exploit human strengths. The development of the automated tools should proceed with the active involvement of both users and trained human factors practitioners. The evaluation of such tools should be carried out with human-in-the-loop simulation and careful experimental design. The introduction of these tools into the workplace should proceed gradually, with adequate attention given to user training, to facility differences, and to user requirements. The operational experience from initial introduction should be very carefully monitored, with mechanisms in place to respond rapidly to the lessons learned from the experiences.
LEVELS OF AUTOMATION
The term automation has been defined in a number of ways in the technical literature. It is defined by some as any introduction of computer technology where it did not exist before. Other definitions restrict the term to computer systems that possess some degree of autonomy. In the Phase I report we defined automation as: "a device or system that accomplishes (partially or fully) a function that was previously carried out (partially or fully) by a human operator." We retain that definition in this volume. For some in the general public the introduction of automation is synonymous with job elimination and worker displacement. In fact, in popular writing, this view leads to concerns that automation is something to be wary or even fearful of. While we acknowledge that automation can have negative, neutral, or even positive implications for job security and worker morale, these issues are not the focus of this report. Rather we use this definition to introduce and evaluate the relationships between individual and system performance on one hand and the design of the kinds of automation that have been proposed to support air traffic controllers, pilots, and other human operators in the safe and efficient management of the national airspace on the other.
In the Phase I report we noted that automation does not refer to a single either-or entity. Rather, forms of automation can be considered to vary across a continuum of levels. The notion of levels of automation has been proposed by several authors (Billings, 1996a, 1996b; Parasuraman et al., 1990; Sheridan, 1980). In this report we expand on that scale in three important directions:
However, a recently completed, independent study (by the Human Factors Subcommittee of the FAA's Research, Engineering, and Development Advisory Council) examined the current FAA organizational structure, staffing, and operating practices as they relate to human factors support activities, making recommendations for improving the effectiveness of this function. These recommendations appear to be well founded and offer the potential for better integration of human factors activities in the development of advanced automation technologies.
The panel recommends that senior Federal Aviation Administration management should reexamine the results of the study by the Human Factors Subcommittee of the FAA's Research, Engineering, and Development Advisory Council, with a view toward implementing those recommendations that appear most likely to achieve more active, continued, and effective involvement of both users and trained human factors practitioners in the development and implementation of advanced air traffic control systems.
All aspects of human-centered automation should be considered in fielding new automated systems. The Federal Aviation Administration should continue to support integrated product teams with well-trained human factors specialists assigned to the teams. Both users and human factors specialists should be involved at the early stages to help define the functionality of the proposed automation system.
These specialists should be responsible to report to human factors management within the Federal Aviation Administration as well as to project managers.
The Federal Aviation Administration should continue to work toward an infrastructure in which some human factors training is provided to personnel and program managers at all levels of the organization (and contract teams).
The Federal Aviation Administration should ensure that adequate funding is provided for needed human factors work at all stages of system development and field evaluations both before and after systems acquisition. During the development of each automation function, system developers should consider possible interactions with other automation functions (under development or already existing), tools, and task requirements that form (or will form) the operational context into which the specific automation feature will be introduced.
AUTOMATION ISSUES AND EMERGING TECHNOLOGIES
This book provides a rationale, based on a human factors perspective, for making decisions about (1) the extent to which automation should be applied to the performance of national airspace system functions and (2) the issues to consider and the methods to apply during design and introduction of systems that incorporate automation to maximize the safety, efficiency, usability, and acceptance of systems that incorporate automation.
The discussion and analysis is divided into three parts: Part I introduces definitions, concepts, and promising emerging technologies; Part II analyzes key automation initiatives; and Part III discusses research and development for the national airspace and presents conclusions and recommendations.
AUTOMATION ISSUES IN AIR TRAFFIC MANAGEMENT
The pressures for automation of the air traffic control system originate from three primary sources: the needs for improved safety, and efficiency (which may include flexibility, potential cost savings, and reductions in staffing); the availability of the technology; and the desire to support the controller. Even given the current very low accident rate in commercial and private aviation, the need remains to strive for even greater safety levels: this is a clearly articulated implication of the ''zero accident" philosophy of the Federal Aviation Administration (FAA) and of current research programs of the National Aeronautics and Space Administration (NASA). Naturally, solutions for improved air traffic safety do not need to be found only in automation; changing procedures, improving training and selection of staff, and introducing technological modernization programs that do not involve automation per se, may be alternative ways of approaching the goal.
The need for improvement is perhaps more strongly driven by the desire to improve efficiency without sacrificing current levels of safety. Efficiency pressures are particularly strong from the commercial air carriers, which operate with very thin profit margins, and for which relatively short delays can translate into very large financial losses. For them it is desirable to substantially increase the existing capacity of the airspace (including its runways) and to minimize disruptions that can be caused by poor weather, inadequate air traffic control equipment, and inefficient air routes. The forecast for the increasing traffic demands over the next several decades exacerbates these pressures.
Of course, as with safety, so with efficiency: advanced air traffic control automation is not the only solution. In particular, the concept of free flight (RTCA,1 1995a, 1995b; Planzer and Jenny, 1995) is a solution that allocates greater responsibility for flight path choice and traffic separation to pilots (i.e., between human elements), rather than necessarily allocating more responsibility to automation. Automation is viewed as a viable alternative solution to solve the demands for increased efficiency. Furthermore, it should be noted that free flight does depend to some extent on advanced automation and also that, from the controller's point of view, the perceived loss of authority whether it is lost to pilots (via free flight) or to automation, may have equivalent human factors implications for design of the controller's workstation.
It is, of course, the case that automation is made possible by the existence of technology. It is also true that, in some domains, automation is driven by the availability of technology; the thinking is, "the automated tools are developed, so they should be used." Developments in sensor technology and artificial intelligence have enabled computers to become better sensors and pattern recognizers, as well as better decision makers, optimizers, and problem solvers.
The extent to which computer skills reach or exceed human capabilities in these endeavors is subject to debate and is certainly quite dependent on context. However, we reject the position that the availability of computer technology should be a reason for automation in and of itself. It should be considered only if such technology has the capability of supporting legitimate system or human operator needs.
Automation has the capability both to compensate for human vulnerabilities and to better support and exploit human strengths. In the Phase I report, we noted controller vulnerabilities (typical of the vulnerabilities of skilled operators in other systems) in the following areas:
Monitoring for and detection of unexpected low-frequency events, Expectancy-driven perceptual processing, Extrapolation of complex four-dimensional trajectories, and Use of working memory to either carry out complex cognitive problem solving or to temporarily retain information. In contrast to these vulnerabilities, when controllers are provided with accurate and enduring (i.e., visual rather than auditory) information, they can be very effective at solving problems, and if such problem solving demands creativity or access to knowledge from more distantly related domains, their problem-solving ability can clearly exceed that of automation. Furthermore, to the extent that accurate and enduring information is shared among multiple operators (i.e., other controllers, dispatchers, and pilots), their collaborative skills in problem solving and negotiation represent important human strengths to be preserved. In many respects, the automated capabilities of data storage, presentation, and communications can facilitate these strengths.
As we discuss further in the following pages, current system needs and the availability of some technology provide adequate justification to continue the development and implementation of some forms of air traffic control automation. But we strongly argue that this continuation should be driven by the philosophy of human-centered automation, which we characterize as follows: The choice of what to automate should be guided by the need to compensate for human vulnerabilities and to exploit human strengths. The development of the automated tools should proceed with the active involvement of both users and trained human factors practitioners. The evaluation of such tools should be carried out with human-in-the-loop simulation and careful experimental design. The introduction of these tools into the workplace should proceed gradually, with adequate attention given to user training, to facility differences, and to user requirements. The operational experience from initial introduction should be very carefully monitored, with mechanisms in place to respond rapidly to the lessons learned from the experiences.
LEVELS OF AUTOMATION
The term automation has been defined in a number of ways in the technical literature. It is defined by some as any introduction of computer technology where it did not exist before. Other definitions restrict the term to computer systems that possess some degree of autonomy. In the Phase I report we defined automation as: "a device or system that accomplishes (partially or fully) a function that was previously carried out (partially or fully) by a human operator." We retain that definition in this volume. For some in the general public the introduction of automation is synonymous with job elimination and worker displacement. In fact, in popular writing, this view leads to concerns that automation is something to be wary or even fearful of. While we acknowledge that automation can have negative, neutral, or even positive implications for job security and worker morale, these issues are not the focus of this report. Rather we use this definition to introduce and evaluate the relationships between individual and system performance on one hand and the design of the kinds of automation that have been proposed to support air traffic controllers, pilots, and other human operators in the safe and efficient management of the national airspace on the other.
In the Phase I report we noted that automation does not refer to a single either-or entity. Rather, forms of automation can be considered to vary across a continuum of levels. The notion of levels of automation has been proposed by several authors (Billings, 1996a, 1996b; Parasuraman et al., 1990; Sheridan, 1980). In this report we expand on that scale in three important directions:
- differentiating the automation of decision and action selection from the automation of information acquisition;
- specifying an upper bound on automation of decision and action selection in terms of task complexity and risk; and
- identifying a third dimension, related to the automation of action implementation.
First, in our view, the original scale best represents the range of automation for decision and action selection. A parallel scale, to be described, can be applied to the information automation. These scales reflect qualitative, relative levels of automation and are not intended to be dimensional, ordinal representations.
Acquisition of information can be considered a separate process from action selection. In both human and machine systems, there are (1) sensors that may vary in their sophistication and adaptability and (2) effectors (actuators) that have feedback control attached to do precise mechanical work according to plan.
Eyes, radars, and information networks are examples of sensors, whereas hands and numerically controlled industrial robots are examples of effectors. We recognize that information acquisition and action selection can and do interact through feedback loops and iteration in both human and machine systems. Nevertheless, it is convenient to consider automation of information acquisition and action selection separately in human-machine systems.
Second, we suggest that specifications for the upper bounds on automation of decision and action selection are contingent on the level of task uncertainty. Finally, we propose a third scale that in this context is dichotomous, related to the automation of action implementation, applicable at the lower levels of automation of decision and action selection.
Information Acquisition
Computer-based automation can apply to any or all of at least six relatively independent features involving operations performed on raw data:
Acquisition of information can be considered a separate process from action selection. In both human and machine systems, there are (1) sensors that may vary in their sophistication and adaptability and (2) effectors (actuators) that have feedback control attached to do precise mechanical work according to plan.
Eyes, radars, and information networks are examples of sensors, whereas hands and numerically controlled industrial robots are examples of effectors. We recognize that information acquisition and action selection can and do interact through feedback loops and iteration in both human and machine systems. Nevertheless, it is convenient to consider automation of information acquisition and action selection separately in human-machine systems.
Second, we suggest that specifications for the upper bounds on automation of decision and action selection are contingent on the level of task uncertainty. Finally, we propose a third scale that in this context is dichotomous, related to the automation of action implementation, applicable at the lower levels of automation of decision and action selection.
Information Acquisition
Computer-based automation can apply to any or all of at least six relatively independent features involving operations performed on raw data:
- Filtering. Filtering involves selecting certain items of information for recommended operator viewing (e.g., a pair of aircraft that would be inferred to be most relevant for conflict avoidance or a set of aircraft within or about to enter a sector). Filtering may be accomplished by guiding the operator to view that information (e.g., highlighting relevant items while graying out less relevant or irrelevant items; Wickens and Yeh, 1996); total filtering may be accomplished by suppressing the display of irrelevant items. Automation devices may vary extensively in terms of how broadly or narrowly they are tuned.
- Information Distribution. Higher levels of automation may flexibly provide more relevant information to specific users, filtering or suppressing the delivery of that same information for whom it is judged to be irrelevant.
- Transformations. Transformations involve operations in which the automation functionality either integrates data (e.g., computing estimated time to contact on the basis of data on position, heading, and velocity from a pair of aircraft) or otherwise performs a mathematical or logical operation on the data (e.g., converting time-to-contact into a priority score). Higher levels of automation transform and integrate raw data into a format that is more compatible with user needs (Vicente and Rasmussen, 1992; Wickens and Carswell, 1995).
- Confidence Estimates. Confidence estimates may be applied at higher levels of automation, when the automated system can express graded levels of certainty or uncertainty regarding the quality of the information it provides (e.g., confidence in resolution and reliability of radar position estimates).
- Integrity Checks. Ensuring the reliability of sensors by connecting and comparing various sensor sources.
- User Request Enabling. User request enabling involves the automation's understanding specific user requests for information to be displayed. If such requests can be understood only if they are expressed in restricted syntax (e.g., a precisely ordered string of specific words or keystrokes), it is a lower level of automation. If requests can be understood in less restricted syntax (e.g., natural language), it is a higher level of automation.
Decision and Action Selection and Action Implementation
Higher levels of automation of decision and action selection define progressively fewer degrees of freedom for humans to select from a wide variety of actions. At levels 2 to 4 on the scale, systems can be developed that allow the operator to execute the advised or recommended action manually (e.g., speaking a clearance) or via automation (e.g., relaying a suggested clearance via data link by a single computer input response). The manual option is not available at the higher levels for automation of decision and action selection. Hence, the dichotomous action implementation scale applies only to the lower levels of automation of decision and action selection.
Finally, we note that control actions can be taken in circumstances that have more or less uncertainty or risk in their consequences, as a result of more or less uncertainty in the environment. For example, the consequences of an automated decision to hand off an aircraft to another controller are easily predictable and of relatively low risk.
In contrast, the consequences of an automation-transmitted clearance or instruction delivered to an aircraft are less certain; for example, the pilot may be unable to comply or may follow the instruction incorrectly. We make the important distinction between lower-level decision actions in the former case (low uncertainty) and higher-level decision actions in the latter case (high uncertainty and risk). Tasks with higher levels of uncertainty should be constrained to lower levels of automation of decision and action selection.
The concluding chapter of the Phase I report examined the characteristics of automation in the current national airspace system. Several aspects of human interaction with automation were examined, both generally and in the specific context of air traffic management. In this chapter, we discuss system reliability and recovery.
SYSTEM PERFORMANCE
System Reliability
Automation is rarely a human factors concern unless it fails or functions in an unintended manner that requires the human operator to become involved. Therefore, of utmost importance for understanding the human factors consequences of automation are the tools for predicting the reliability (inverse of failure rate) of automated systems. We consider below some of the strengths and limitations of reliability analysis.
Analysis Techniques
Reliability analysis, and its closely related methodology of probabilistic risk assessment, have been used to determine the probability of major system failure for nuclear power plants, and similar applications may be forthcoming for air traffic control systems. There are several popular techniques that are used together.
One is fault tree analysis (Kirwan and Ainsworth, 1992), wherein one works backward from the "top event," the failure of some high-level function, and what major systems must have failed in order for this failure to occur. This is usually expressed in terms of a fault tree, a graphical diagram of systems with ands and ors on the links connecting the second-level subsystems to the top-level system representation. For example, radar fails if any of the following fails: the radar antennas and drives, or the computers that process the radar signals, or the radar displays, or the air traffic controller's attention to the displays. This amounts to four nodes connected by or links to the node representing failure of the radar function. At a second level, for example, computer failure occurs if both the primary and the backup computers fail. Each computer, in turn, can experience a software failure or a hardware failure or a power failure or failure because of an operator error. In this way, one builds up a tree that branches downward from the top event according to the and-/or-gate logic of both machine and human elements interacting. The analysis can be carried downward to any level of detail. By putting probabilities on the events, one can study their effects on the top event. As may be realized by the above example, system components depending on and-gate inputs are far more robust to failures (and hence reliable) than those depending on or-gate inputs.
Another popular technique is event tree analysis. Starting from some malfunction, the analyst considers what conditions may lead to other possible (and probably more serious) malfunctions, and from the latter malfunction what conditions may produce further malfunctions. Again, probabilities may be assigned to study the relative effects on producing the most serious (downstream) malfunctions. Such techniques can provide two sorts of outputs (there are others, such as cause-consequence diagrams, safety-state Markov diagrams, etc.; Idaho National Engineering Laboratory, 1997). On one hand, they may produce what appear to be "hard numbers" indicating the overall system reliability (e.g., .997). For reasons we describe below, such numbers must be treated with extreme caution.
On the other hand, reliability analysis may allow one to infer the most critical functions of the human operator relative to the machinery. In one such study performed in the nuclear safety context, Hall et al. (1981) showed the insights that can be gained without even knowing precisely the probabilities for human error. They simply assumed human error rates (for given machine error rates) and performed the probability analysis repeatedly with different multipliers on the human error rate. The computer, after all, can do this easily once the fault tree or event tree structure is programmed in. The authors were able to discover the circumstances for which human error made a big difference, and when it did not. Finally, it should be noted that the very process of carrying out reliability analysis can act as a sort of audit trail, to ensure that the consequences of various improbable but not impossible events are considered.
Although reliability analysis is a potentially valuable tool for understanding the sensitivity of system performance to human error (human "failure"), as we noted above, one must use great caution in trusting the absolute numbers that may be produced, for example, using these numbers as targets for system design, as was done with the advanced automation system (AAS). There are at least four reasons for such caution, two of which we discuss briefly, and two in greater depth. In the first place, any such number (i.e., r = .997) is an estimate of a mean. But what must be considered in addition is the estimate of the variability around that mean, to determine best-case and worst-case situations. Variance estimates tend to be very large relative to the mean for probabilities that are very close to 0 or 1.0. And with large variance estimates (uncertainty of the mean), the mean value itself has less meaning.
A second problem with reliability analysis pertains to unforeseen events. It seems to be a given that things can fail in the world, failures that the analysts have no way of predicting. For example, it is doubtful that any reliability analyst would have been able to project, in advance, the likelihood that a construction worker would sever the power supply to the New York TRACON with a backhoe loader, let alone have provided a reliable estimate of the probability of such an event's occurring.
The two further concerns related to the hard numbers of reliability analysis are the extreme difficulties of making reliability estimates of two critical components in future air traffic control automation: the human and the software. Because of their importance, each of these is dealt with in some detail.
Human Reliability Analysis
Investigators in the nuclear power industry have proposed that engineering reliability analysis can be extended to incorporate the human component (Swain, 1990; Miller and Swain, 1987). If feasible, such extension would be extremely valuable in air traffic control, given the potential for two kinds of human error to contribute to the loss of system reliability: errors in actual operation (e.g., a communications misunderstanding, an overlooked altitude deviation) and errors in system set-up or maintenance. Some researchers have pointed out the difficulty of applying human reliability analysis (to derive hard numbers, as opposed to doing the sort of sensitivity analysis described above).
The fundamental difficulties of this technique revolve around the estimation of the component reliabilities and their aggregation through traditional analysis techniques. For example, it is very hard to get meaningful estimates of human error rates, because human error is so context driven (e.g., by fatigue, stress, expertise level) and because the source of cognitive errors remains poorly understood. Although this work has progressed, massive data collection efforts will be necessary in the area of air traffic control, in order to form even partially reliable estimates of these rates.
A second criticism concerns the general assumptions of independence that underlie the components in an event or fault tree. Events at levels above (in a fault tree) or below (in an event tree) are assumed to be independent, yet human operators show two sorts of dependencies that are difficult to predict or quantify (Adams, 1982).
For one thing, there are possible dependencies between two human components. For example, the developmental controller may be reluctant to call into question an error that he or she noticed that was committed by a more senior, full-performance-level controller at the same console. For another thing, there are poorly understood dependencies between human and system reliabilities, related to trust calibration, which we discuss later in this chapter. For example, a controller may increase his or her own level of vigilance to compensate for an automated component that is known to be unreliable; alternatively, in the face of frustration with the system, a controller may become stressed or confused and show decreased reliability.
Software Reliability Analysis
Hardware reliability is generally a function of manufacturing failures or the wearing out of components. With sophisticated testing, it is possible to predict how reliable a piece of hardware will be according to measures such as mean time between failures. Measuring software reliability, however, is a much more difficult problem. For the most part, software systems need to fail in real situations, in order to discover bugs.
Generally, many uses are required before a piece of software is considered reliable. According to Parnas et al. (1990), failures in software are the result of unpredictable input sequences. Predicting failure rate is based on the probability of encountering an input sequence that will cause the system to fail. Trustworthiness is defined by the extent to which a catastrophic failure or error may occur; software is trusted to the extent that the probability of a serious flaw is low. Testing for trustworthiness is difficult because the number of states and possible input sequences is so large that the probability of an error's escaping attention is high.
For example, the loss of the Airbus A330 in Toulouse in June 1994 (Dornheim, 1995) was attributed to autoflight logic behavior changing dramatically under unanticipated circumstances. In the altitude capture mode, the software creates a table of vertical speed versus time to achieve smooth level-off. This is a fixed table based on the conditions at the time the mode is activated. In this case, due to the timing of events involving a simulated engine failure, the automation continued to operate as though full power from both engines was available. The result was steep pitchup and loss of air speedthe aircraft went out of control and crashed.
There are a number of factors that contribute to the difficulty of designing highly reliable software. First is complexity. Even with small software systems, it is common to find that a programmer requires a year of working with the program before he or she can be trusted to make improvements on his or her own. Second is sensitivity to error. In manufacturing, hardware products are designed within certain acceptable tolerances for error; it is possible to have small errors with small consequences. In software, however, tolerance is not a useful concept because trivial clerical errors can have major consequences.
Third, it is difficult to test software adequately. Since mathematical functions implemented by software are not continuous, it is necessary to perform an extremely large number of tests. In continuous function systems, testing is based on interpolation between two pointsdevices that function well on two close points are assumed to function well at all points in between.
This assumption is not possible for software, and because of the large number of states it is not possible to do enough testing to ensure that the software is correct. If there is a good model of operating conditions, then software reliability can be predicted using mathematical models. Generally, good models of operating conditions are not available until after the software is developed.
Some steps can be taken to reduce the probability of errors in software. Among them is conducting independent validation using researchers and testing personnel who were not involved in development. Another is to ensure that the software is well documented and structured for review. Reviews should cover the following questions:
Are the correct functions included?
Is the software maintainable?
For each module, are the algorithms and data structures consistent with the specified behavior?
Are codes consistent with algorithms and data structures?
Are the tests adequate?
Yet another step is to develop professional standards for software engineers that include an agreed-upon set of skills and knowledge.
Recently, the capacity maturity model (CMM) for software has been proposed as a framework for encouraging effective software development. This model covers practices of planning, engineering, and managing software development and maintenance. It is intended to improve the ability of organizations to meet goals for cost, schedule, functionality, and product quality. The model includes five levels of achieving a mature software process. Organizations at the highest level can be characterized as continuously improving the range of their process capability and thereby improving the performance of their projects. Innovations that use the best software engineering practices are identified and transferred throughout the organization. In addition, these organizations use data on the effectiveness of software to perform cost-benefit analyses of new technologies as well as proposed changes to the software development process.
Conclusion
Although the concerns described above collectively suggest extreme caution in trusting the mean numbers that emerge from a reliability analysis conducted on complex human-machine systems like air traffic control, we wish to reiterate the importance of such analyses in two contexts. First, merely carrying out the analysis can provide the designer with a better understanding of the relationships between components and can reveal sources of possible failures for which safeguards can be built. Second, appropriate use of the tools can provide good sensitivity analyses of the importance (in some conditions) or nonimportance (in others) of human failure.
Higher levels of automation of decision and action selection define progressively fewer degrees of freedom for humans to select from a wide variety of actions. At levels 2 to 4 on the scale, systems can be developed that allow the operator to execute the advised or recommended action manually (e.g., speaking a clearance) or via automation (e.g., relaying a suggested clearance via data link by a single computer input response). The manual option is not available at the higher levels for automation of decision and action selection. Hence, the dichotomous action implementation scale applies only to the lower levels of automation of decision and action selection.
Finally, we note that control actions can be taken in circumstances that have more or less uncertainty or risk in their consequences, as a result of more or less uncertainty in the environment. For example, the consequences of an automated decision to hand off an aircraft to another controller are easily predictable and of relatively low risk.
In contrast, the consequences of an automation-transmitted clearance or instruction delivered to an aircraft are less certain; for example, the pilot may be unable to comply or may follow the instruction incorrectly. We make the important distinction between lower-level decision actions in the former case (low uncertainty) and higher-level decision actions in the latter case (high uncertainty and risk). Tasks with higher levels of uncertainty should be constrained to lower levels of automation of decision and action selection.
The concluding chapter of the Phase I report examined the characteristics of automation in the current national airspace system. Several aspects of human interaction with automation were examined, both generally and in the specific context of air traffic management. In this chapter, we discuss system reliability and recovery.
SYSTEM PERFORMANCE
System Reliability
Automation is rarely a human factors concern unless it fails or functions in an unintended manner that requires the human operator to become involved. Therefore, of utmost importance for understanding the human factors consequences of automation are the tools for predicting the reliability (inverse of failure rate) of automated systems. We consider below some of the strengths and limitations of reliability analysis.
Analysis Techniques
Reliability analysis, and its closely related methodology of probabilistic risk assessment, have been used to determine the probability of major system failure for nuclear power plants, and similar applications may be forthcoming for air traffic control systems. There are several popular techniques that are used together.
One is fault tree analysis (Kirwan and Ainsworth, 1992), wherein one works backward from the "top event," the failure of some high-level function, and what major systems must have failed in order for this failure to occur. This is usually expressed in terms of a fault tree, a graphical diagram of systems with ands and ors on the links connecting the second-level subsystems to the top-level system representation. For example, radar fails if any of the following fails: the radar antennas and drives, or the computers that process the radar signals, or the radar displays, or the air traffic controller's attention to the displays. This amounts to four nodes connected by or links to the node representing failure of the radar function. At a second level, for example, computer failure occurs if both the primary and the backup computers fail. Each computer, in turn, can experience a software failure or a hardware failure or a power failure or failure because of an operator error. In this way, one builds up a tree that branches downward from the top event according to the and-/or-gate logic of both machine and human elements interacting. The analysis can be carried downward to any level of detail. By putting probabilities on the events, one can study their effects on the top event. As may be realized by the above example, system components depending on and-gate inputs are far more robust to failures (and hence reliable) than those depending on or-gate inputs.
Another popular technique is event tree analysis. Starting from some malfunction, the analyst considers what conditions may lead to other possible (and probably more serious) malfunctions, and from the latter malfunction what conditions may produce further malfunctions. Again, probabilities may be assigned to study the relative effects on producing the most serious (downstream) malfunctions. Such techniques can provide two sorts of outputs (there are others, such as cause-consequence diagrams, safety-state Markov diagrams, etc.; Idaho National Engineering Laboratory, 1997). On one hand, they may produce what appear to be "hard numbers" indicating the overall system reliability (e.g., .997). For reasons we describe below, such numbers must be treated with extreme caution.
On the other hand, reliability analysis may allow one to infer the most critical functions of the human operator relative to the machinery. In one such study performed in the nuclear safety context, Hall et al. (1981) showed the insights that can be gained without even knowing precisely the probabilities for human error. They simply assumed human error rates (for given machine error rates) and performed the probability analysis repeatedly with different multipliers on the human error rate. The computer, after all, can do this easily once the fault tree or event tree structure is programmed in. The authors were able to discover the circumstances for which human error made a big difference, and when it did not. Finally, it should be noted that the very process of carrying out reliability analysis can act as a sort of audit trail, to ensure that the consequences of various improbable but not impossible events are considered.
Although reliability analysis is a potentially valuable tool for understanding the sensitivity of system performance to human error (human "failure"), as we noted above, one must use great caution in trusting the absolute numbers that may be produced, for example, using these numbers as targets for system design, as was done with the advanced automation system (AAS). There are at least four reasons for such caution, two of which we discuss briefly, and two in greater depth. In the first place, any such number (i.e., r = .997) is an estimate of a mean. But what must be considered in addition is the estimate of the variability around that mean, to determine best-case and worst-case situations. Variance estimates tend to be very large relative to the mean for probabilities that are very close to 0 or 1.0. And with large variance estimates (uncertainty of the mean), the mean value itself has less meaning.
A second problem with reliability analysis pertains to unforeseen events. It seems to be a given that things can fail in the world, failures that the analysts have no way of predicting. For example, it is doubtful that any reliability analyst would have been able to project, in advance, the likelihood that a construction worker would sever the power supply to the New York TRACON with a backhoe loader, let alone have provided a reliable estimate of the probability of such an event's occurring.
The two further concerns related to the hard numbers of reliability analysis are the extreme difficulties of making reliability estimates of two critical components in future air traffic control automation: the human and the software. Because of their importance, each of these is dealt with in some detail.
Human Reliability Analysis
Investigators in the nuclear power industry have proposed that engineering reliability analysis can be extended to incorporate the human component (Swain, 1990; Miller and Swain, 1987). If feasible, such extension would be extremely valuable in air traffic control, given the potential for two kinds of human error to contribute to the loss of system reliability: errors in actual operation (e.g., a communications misunderstanding, an overlooked altitude deviation) and errors in system set-up or maintenance. Some researchers have pointed out the difficulty of applying human reliability analysis (to derive hard numbers, as opposed to doing the sort of sensitivity analysis described above).
The fundamental difficulties of this technique revolve around the estimation of the component reliabilities and their aggregation through traditional analysis techniques. For example, it is very hard to get meaningful estimates of human error rates, because human error is so context driven (e.g., by fatigue, stress, expertise level) and because the source of cognitive errors remains poorly understood. Although this work has progressed, massive data collection efforts will be necessary in the area of air traffic control, in order to form even partially reliable estimates of these rates.
A second criticism concerns the general assumptions of independence that underlie the components in an event or fault tree. Events at levels above (in a fault tree) or below (in an event tree) are assumed to be independent, yet human operators show two sorts of dependencies that are difficult to predict or quantify (Adams, 1982).
For one thing, there are possible dependencies between two human components. For example, the developmental controller may be reluctant to call into question an error that he or she noticed that was committed by a more senior, full-performance-level controller at the same console. For another thing, there are poorly understood dependencies between human and system reliabilities, related to trust calibration, which we discuss later in this chapter. For example, a controller may increase his or her own level of vigilance to compensate for an automated component that is known to be unreliable; alternatively, in the face of frustration with the system, a controller may become stressed or confused and show decreased reliability.
Software Reliability Analysis
Hardware reliability is generally a function of manufacturing failures or the wearing out of components. With sophisticated testing, it is possible to predict how reliable a piece of hardware will be according to measures such as mean time between failures. Measuring software reliability, however, is a much more difficult problem. For the most part, software systems need to fail in real situations, in order to discover bugs.
Generally, many uses are required before a piece of software is considered reliable. According to Parnas et al. (1990), failures in software are the result of unpredictable input sequences. Predicting failure rate is based on the probability of encountering an input sequence that will cause the system to fail. Trustworthiness is defined by the extent to which a catastrophic failure or error may occur; software is trusted to the extent that the probability of a serious flaw is low. Testing for trustworthiness is difficult because the number of states and possible input sequences is so large that the probability of an error's escaping attention is high.
For example, the loss of the Airbus A330 in Toulouse in June 1994 (Dornheim, 1995) was attributed to autoflight logic behavior changing dramatically under unanticipated circumstances. In the altitude capture mode, the software creates a table of vertical speed versus time to achieve smooth level-off. This is a fixed table based on the conditions at the time the mode is activated. In this case, due to the timing of events involving a simulated engine failure, the automation continued to operate as though full power from both engines was available. The result was steep pitchup and loss of air speedthe aircraft went out of control and crashed.
There are a number of factors that contribute to the difficulty of designing highly reliable software. First is complexity. Even with small software systems, it is common to find that a programmer requires a year of working with the program before he or she can be trusted to make improvements on his or her own. Second is sensitivity to error. In manufacturing, hardware products are designed within certain acceptable tolerances for error; it is possible to have small errors with small consequences. In software, however, tolerance is not a useful concept because trivial clerical errors can have major consequences.
Third, it is difficult to test software adequately. Since mathematical functions implemented by software are not continuous, it is necessary to perform an extremely large number of tests. In continuous function systems, testing is based on interpolation between two pointsdevices that function well on two close points are assumed to function well at all points in between.
This assumption is not possible for software, and because of the large number of states it is not possible to do enough testing to ensure that the software is correct. If there is a good model of operating conditions, then software reliability can be predicted using mathematical models. Generally, good models of operating conditions are not available until after the software is developed.
Some steps can be taken to reduce the probability of errors in software. Among them is conducting independent validation using researchers and testing personnel who were not involved in development. Another is to ensure that the software is well documented and structured for review. Reviews should cover the following questions:
Are the correct functions included?
Is the software maintainable?
For each module, are the algorithms and data structures consistent with the specified behavior?
Are codes consistent with algorithms and data structures?
Are the tests adequate?
Yet another step is to develop professional standards for software engineers that include an agreed-upon set of skills and knowledge.
Recently, the capacity maturity model (CMM) for software has been proposed as a framework for encouraging effective software development. This model covers practices of planning, engineering, and managing software development and maintenance. It is intended to improve the ability of organizations to meet goals for cost, schedule, functionality, and product quality. The model includes five levels of achieving a mature software process. Organizations at the highest level can be characterized as continuously improving the range of their process capability and thereby improving the performance of their projects. Innovations that use the best software engineering practices are identified and transferred throughout the organization. In addition, these organizations use data on the effectiveness of software to perform cost-benefit analyses of new technologies as well as proposed changes to the software development process.
Conclusion
Although the concerns described above collectively suggest extreme caution in trusting the mean numbers that emerge from a reliability analysis conducted on complex human-machine systems like air traffic control, we wish to reiterate the importance of such analyses in two contexts. First, merely carrying out the analysis can provide the designer with a better understanding of the relationships between components and can reveal sources of possible failures for which safeguards can be built. Second, appropriate use of the tools can provide good sensitivity analyses of the importance (in some conditions) or nonimportance (in others) of human failure.
System Failure and Recovery
Less than perfect reliability means that automation-related system failures can degrade system performance. Later in this chapter we consider the human performance issues associated with the response to such failures and automation-related anomalies in general. Here we address the broader issue of failure recovery from a system-wide perspective. We first consider some of the generic properties of failure modes that affect system recovery and then provide the framework for a model of failure recoverythat is, the capability of the team of human controllers to recover and restore safety to an airspace within which some aspect of computer automation has failed.
We distinguish here between system failures and human operator (i.e., controllers) failures or errors. The latter are addressed later in this chapter and in the Phase I report. System failures are often due to failures or errors of the humans involved with other aspects of the air traffic control system. They include system designers, whose design fails to anticipate certain characteristics of operations; those involved in fabrication, test, and certification; and system maintainers. Personnel at any of these levels can be responsible for a ''failure event" imposed on air traffic control staff controlling live traffic. It is the nature of such an event that concerns us here. We also use the term system failure to include relatively catastrophic failures of aircraft handling because of mechanical damage or undesirable pilot behavior.
System failures can differ in their severity, their time course, their complexity, and the existing conditions at the time of the failure.
We distinguish here between system failures and human operator (i.e., controllers) failures or errors. The latter are addressed later in this chapter and in the Phase I report. System failures are often due to failures or errors of the humans involved with other aspects of the air traffic control system. They include system designers, whose design fails to anticipate certain characteristics of operations; those involved in fabrication, test, and certification; and system maintainers. Personnel at any of these levels can be responsible for a ''failure event" imposed on air traffic control staff controlling live traffic. It is the nature of such an event that concerns us here. We also use the term system failure to include relatively catastrophic failures of aircraft handling because of mechanical damage or undesirable pilot behavior.
System failures can differ in their severity, their time course, their complexity, and the existing conditions at the time of the failure.
- Severity differences relate to the system safety consequences. For example, a failed light on a console can be easily noticed and replaced, with minimal impact on safe traffic handling. A failed radar display will have a more serious impact, and a failed power supply to an entire facility will have consequences that are still more serious. As we detail below, the potential seriousness of failures is related to existing conditions.
- In terms of time courses, failures may be abrupt (catastrophic), intermittent, or gradual. Abrupt failures, like a power outage, are to some extent more serious because they allow the operator little time to prepare for intervention. At the same time, they do have the advantage of being more noticeable, whereas gradual failures may degrade system capabilities in ways that are not noticeable e.g., the gradual loss of resolution of a sensor, like a radar. Intermittent failures are also inherently difficult to diagnose because of the difficulty in confirming the diagnosis.
- Complexity refers to single versus multiple component failures. The latter may be common mode failures (such as the loss of power, which will cause several components to fail simultaneously, or the overload on computer capacity), or they may be independent mode failures, when two things go wrong independently, creating a very difficult diagnostic chore (Sanderson and Martagh, 1989). Independent mode failures are extremely rare, as classical reliability analysis will point out, but are not inconceivable, and their rarity itself presents a particular challenge for diagnosis by the operator who does not expect them.
- Existing conditions refer to the conditions that exist when a failure occurs. These will readily affect the ease of recovery and, hence indirectly, the severity of the consequence. For example, failure of radar will be far more severe in a saturated airspace during a peak rush period than in an empty one at 3:00 a.m. We address this issue in discussing failure recovery.
Because automation is not a single entity, its consequences will vary greatly, depending on what is automated (e.g., information acquisition or control action). Next to the right in the figure is a set of variables, assumed to be influenced by the introduction of automation (the list is not exhaustive and does not incorporate organizational issues, like job satisfaction and morale). Associated with each variable is a sign (or set of signs) indicating the extent to which the introduction of automation is likely to increase or decrease the variable in question. These variables are described in the next sections.
Capacity
One motivation for introducing automation at this time is increasing airspace capacity and traffic flow efficiency. It is therefore likely that any automation tool that is introduced will increase (+) capacity.
Traffic Density
Automation may or may not increase traffic density. For example, automation that can reduce the local bunching of aircraft at certain times and places will serve to increase capacity, leaving overall density unaffected. Therefore, two possible effects (+ and 0) may be associated with density.
Complexity
Automation will probably increase the complexity of the airspace, to the extent that it induces changes in traffic flow that depart from the standard air routes and provides flight trajectories that are more tailored to the capabilities of individual aircraft and less consistent from day to day.
Situation Awareness and Workload
Automation is often assumed to reduce the human operator's situation awareness (Endsley, 1996a). However, this is not a foregone conclusion because of differences in the nature of automation and its relation to workload. For example, as we propose in the framework presented in Figure 1.2, automation of information integration in the cockpit can provide information in a manner that is more readily interpretable and hence may improve situation awareness and human response to system failures. In the context of information integration in air traffic management, four-dimensional flight path projections may serve this purpose. Correspondingly, automation may sometimes serve to reduce workload to manageable.
Where two nodes are connected by an arrow, signs (+, -, 0) indicate the direction of effect on the variable depicted in the right node, caused by an increase in the variable depicted in the left node. levels, such that the controller has more cognitive resources available to maintain situation awareness. This is the reasoning behind the close link with workload. However, the figure reflects the assumption that the increasing (+) influence of automation on traffic complexity and density will impose a decrease (-) on situation awareness. The effect of increasing traffic complexity on situation awareness will be direct. The effect of traffic density will be mediated by the effect of density on workload. Higher monitoring workload caused by higher traffic density will be likely to degrade situation awareness.
Skill Degradation
There is little doubt that automation of most functions eventually degrades the manual skills for most functions one might automate, given the nearly universal findings of forgetting and skill decay with disuse reported in the behavioral literature (Wickens, 1992), although the magnitude of decline in air traffic control skills with disuse is not well known. For example, suppose predictive functions are automated, enabling controllers to more easily envision future conflicts. Although the controllers' ability to mentally extrapolate trajectories may eventually decay, their ability to solve conflict problems may actually benefit from this better perceptual information, leading possibly to a net gain in overall control ability.
Recovery Response Time
Linking the two human performance elements, situation awareness change and skill degradation, makes it possible to predict the change in recovery response time, that is, the time required to respond to unexpected failure situations and possibly intervene with manual control skills. It is assumed that a less skilled controller (one with degraded skills), responding appropriately to a situation of which he has less awareness, will do so more slowly. This outcome variable is labeled recovery response time (we acknowledge that it could also incorporate the accuracy, efficiency, or appropriateness of the response). Such a time function is a special case of more general workload models in which workload is defined in terms of the ratio of time required to time available. As an example, in a current air traffic control scenario, when a transgression of one aircraft into the path of another on a parallel runway approach occurs, the ratio of the time required to respond to the time available has a critical bearing on traffic safety.
A plausible, but hypothetical function relating recovery response time to the level of automation, mediated by the variables in the middle of the figure, is shown by the dashed line in the graph to the right of the figure, increasing as the level of automation increases. It may also be predicted that recovery response time will be greatly modulated by individual skill differences, by the redundant characteristics of the team environment, by the complexity of the problem, and by the degree to which the failure is expected.
At the top of the figure, we see that failures will be generated probabilistically and may be predicted by failure models, or failure scenario generators, which take into account the reliability of the equipment, of the design, of operators in the system, of weather forecasting, and of the robustness (fault tolerance) of the system. When a failure does occur, its effect on system safety will be directly modulated by the vulnerability of the system, which itself should be directly related to the density. If aircraft are more closely spaced, there is far less time available to respond appropriately with a safe solution, and fewer solutions are available. In the extreme case, if aircraft are too closely spaced, no solutions are available.
The solid line of the graph reflects the increasing vulnerability of the system, resulting from the density-increasing influences of higher automation levels in terms of the time available to respond to a failure. Thus, the graph overlays the two critical time variables against each other: the time required to ensure safe separation of aircraft, given a degraded air traffic control system (a range that could include best case, worst case, median estimates, etc.) and the time available for a controller team to intervene and safely recover from the failure, both as functions of the automation-induced changes in the intervening process variables.
We may plausibly argue that the all-important safety consequences of automation are related to the margin by which time available exceeds the recovery response time. There are a number of possible sources of data that may begin to provide some quantitative input to the otherwise qualitative model of influences shown in the figure.
For example, work by Odoni et al. (1997) on synthesizing and summarizing models appears to be the best source of information on modeling how capacity and density changes, envisioned by automated products, will influence vulnerability. Work conducted at Sandia Laboratory for the Nuclear Regulatory Commission may prove fruitful in generating possible failure scenarios (Swain and Guttman, 1983). Airspace safety models need to be developed that can predict the likelihood of actual midair collisions, as a function of the likelihood and parameters of near-midair collisions and losses of separation and of decreases in traffic separation.
Turning to the human component, promising developments are taking place under the auspices of NASA's advanced air transportation technology program, in terms of developing models of pilots' response time to conflict situations.
Capacity
One motivation for introducing automation at this time is increasing airspace capacity and traffic flow efficiency. It is therefore likely that any automation tool that is introduced will increase (+) capacity.
Traffic Density
Automation may or may not increase traffic density. For example, automation that can reduce the local bunching of aircraft at certain times and places will serve to increase capacity, leaving overall density unaffected. Therefore, two possible effects (+ and 0) may be associated with density.
Complexity
Automation will probably increase the complexity of the airspace, to the extent that it induces changes in traffic flow that depart from the standard air routes and provides flight trajectories that are more tailored to the capabilities of individual aircraft and less consistent from day to day.
Situation Awareness and Workload
Automation is often assumed to reduce the human operator's situation awareness (Endsley, 1996a). However, this is not a foregone conclusion because of differences in the nature of automation and its relation to workload. For example, as we propose in the framework presented in Figure 1.2, automation of information integration in the cockpit can provide information in a manner that is more readily interpretable and hence may improve situation awareness and human response to system failures. In the context of information integration in air traffic management, four-dimensional flight path projections may serve this purpose. Correspondingly, automation may sometimes serve to reduce workload to manageable.
Where two nodes are connected by an arrow, signs (+, -, 0) indicate the direction of effect on the variable depicted in the right node, caused by an increase in the variable depicted in the left node. levels, such that the controller has more cognitive resources available to maintain situation awareness. This is the reasoning behind the close link with workload. However, the figure reflects the assumption that the increasing (+) influence of automation on traffic complexity and density will impose a decrease (-) on situation awareness. The effect of increasing traffic complexity on situation awareness will be direct. The effect of traffic density will be mediated by the effect of density on workload. Higher monitoring workload caused by higher traffic density will be likely to degrade situation awareness.
Skill Degradation
There is little doubt that automation of most functions eventually degrades the manual skills for most functions one might automate, given the nearly universal findings of forgetting and skill decay with disuse reported in the behavioral literature (Wickens, 1992), although the magnitude of decline in air traffic control skills with disuse is not well known. For example, suppose predictive functions are automated, enabling controllers to more easily envision future conflicts. Although the controllers' ability to mentally extrapolate trajectories may eventually decay, their ability to solve conflict problems may actually benefit from this better perceptual information, leading possibly to a net gain in overall control ability.
Recovery Response Time
Linking the two human performance elements, situation awareness change and skill degradation, makes it possible to predict the change in recovery response time, that is, the time required to respond to unexpected failure situations and possibly intervene with manual control skills. It is assumed that a less skilled controller (one with degraded skills), responding appropriately to a situation of which he has less awareness, will do so more slowly. This outcome variable is labeled recovery response time (we acknowledge that it could also incorporate the accuracy, efficiency, or appropriateness of the response). Such a time function is a special case of more general workload models in which workload is defined in terms of the ratio of time required to time available. As an example, in a current air traffic control scenario, when a transgression of one aircraft into the path of another on a parallel runway approach occurs, the ratio of the time required to respond to the time available has a critical bearing on traffic safety.
A plausible, but hypothetical function relating recovery response time to the level of automation, mediated by the variables in the middle of the figure, is shown by the dashed line in the graph to the right of the figure, increasing as the level of automation increases. It may also be predicted that recovery response time will be greatly modulated by individual skill differences, by the redundant characteristics of the team environment, by the complexity of the problem, and by the degree to which the failure is expected.
At the top of the figure, we see that failures will be generated probabilistically and may be predicted by failure models, or failure scenario generators, which take into account the reliability of the equipment, of the design, of operators in the system, of weather forecasting, and of the robustness (fault tolerance) of the system. When a failure does occur, its effect on system safety will be directly modulated by the vulnerability of the system, which itself should be directly related to the density. If aircraft are more closely spaced, there is far less time available to respond appropriately with a safe solution, and fewer solutions are available. In the extreme case, if aircraft are too closely spaced, no solutions are available.
The solid line of the graph reflects the increasing vulnerability of the system, resulting from the density-increasing influences of higher automation levels in terms of the time available to respond to a failure. Thus, the graph overlays the two critical time variables against each other: the time required to ensure safe separation of aircraft, given a degraded air traffic control system (a range that could include best case, worst case, median estimates, etc.) and the time available for a controller team to intervene and safely recover from the failure, both as functions of the automation-induced changes in the intervening process variables.
We may plausibly argue that the all-important safety consequences of automation are related to the margin by which time available exceeds the recovery response time. There are a number of possible sources of data that may begin to provide some quantitative input to the otherwise qualitative model of influences shown in the figure.
For example, work by Odoni et al. (1997) on synthesizing and summarizing models appears to be the best source of information on modeling how capacity and density changes, envisioned by automated products, will influence vulnerability. Work conducted at Sandia Laboratory for the Nuclear Regulatory Commission may prove fruitful in generating possible failure scenarios (Swain and Guttman, 1983). Airspace safety models need to be developed that can predict the likelihood of actual midair collisions, as a function of the likelihood and parameters of near-midair collisions and losses of separation and of decreases in traffic separation.
Turning to the human component, promising developments are taking place under the auspices of NASA's advanced air transportation technology program, in terms of developing models of pilots' response time to conflict situations.
- The traffic management advisor (TMA) supports the TRACON and en route traffic management controllers, primarily in developing an optimal plan, to assign each aircraft a scheduled time of arrival at a downstream point, like a final approach fix or runway threshold, and a sequence of arrival, relative to other aircraft approaching the terminal area. The traffic management advisor begins to compute these for inbound aircraft at a point about 200 miles or 45 minutes from the final approach. The plan is designed to optimize the overall flow of the set of aircraft, as well as the fuel consumption of each individual aircraft. At the same time, it accounts for various constraints on runway availability and aircraft maneuverability. The plan is also accompanied by an assessment of flight path changes to be implemented in order to accomplish the plan. A set of three displays assists the traffic management coordinator in evaluating the plan. These include a time line of scheduled and estimated times of arrivals for the aircraft, a listing of alternative runway configurations, and a load graph, which indicates the anticipated traffic load across designated points in the airspace in 15-minute increments. The displays can be presented in large-screen formats for group viewing. The actual implementation of the plan generated by the traffic management coordinator with the assistance of the traffic management advisor is carried out by the other two elements of CTAS, the descent advisor, and the final approach spacing tool.
- The descent advisor (DA) provides controllers at the final sector of the enroute center with advice on proper speed, altitude, and (occasionally) heading control necessary to accomplish the plan generated by the traffic management advisor. The critical algorithm underlying the descent advisor is a four-dimensional predictor that is individually tailored for each aircraft, based on that aircraft's type and preferred maneuver, along with local atmospheric data. This predictor generates a set of possible trajectories for the aircraft to implement the traffic management advisor plan. The descent advisor then provides the controller with a set of advisories regarding speed, top of descent point, and descent speed. In cases in which these parameters are not sufficient to accomplish the plan, path stretching advisories are offered that advise lateral maneuvers. The descent advisor also contains a conflict probe that will monitor for possible conflicts up to 20 minutes ahead. If such conflicts are detected, it will offer resolution advisories, based initially on speed and altitude changes. If none of these is feasible, lateral maneuvers will be offered as a solution.
- The final approach spacing tool (FAST) is the corresponding advisory tool designed to support the TRACON controller in implementing the traffic management advisor plan, by issuing speed and heading advisories and runway assignments necessary to maintain optimal spacing between aircraft of different classes. An important secondary function of the final approach spacing tool is its ability to rapidly adjust to and reschedule on the basis of unexpected events like a missed approach or a sudden unexpected runway closure. Like the descent advisor, the controller receives advice in the fourth line of the data tag, and also has access to time lines. The final approach spacing tool exists in two versions: the passive FAST provides only aircraft sequence and runway assignments, and the active FAST includes speed and heading advisories.
A system with similar functions, known as COMPAS (computer-oriented metering planning and advisory system), was developed by the German Aerospace Research Establishment and has been operational in Frankfurt since 1991 (Völckers, 1991). The system attempts to assist the controller in the planning and control of approach traffic. Based on flight plans and radar data, the system calculates the arrival time of each aircraft, taking into consideration such parameters as aircraft performance, traffic proximity, and wake vortex separation minima. On the basis of these calculated arrival times, the system establishes a landing sequence, as well as a nominal gate arrival time for each aircraft. The difference between the calculated time and the nominal time is then transformed into a medium-term plan by which traffic flow can be smoothed, starting outside the terminal area. The goal of this plan is to reduce aggregate delay across the entire traffic stream.
The interface for the COMPAS presents the controller with a sequencing time line, with arrivals ordered from latest to earliest, top to bottom. The time associated with each aircraft represents the estimated arrival time, over either the metering fix (in the case of the en route controller) or the approach gate (for the approach controller). Aircraft weight class and approach direction are represented in the display. The control advisories themselves are presented as one of four possible characters beside the aircraft label: X to expedite up to two minutes, O for no action, R for delay up to four minutes, and H to hold for more than four minutes.
Operational experience with COMPAS has demonstrated reductions in planning and coordination workload, as well as reductions in the time spent on coordination and smoothing of the traffic flow in the terminal area.
Notice that COMPAS provides general resolution advisories (e.g., ''hold for more than four minutes"); the descent advisor of CTAS provides another level of assistancenamely, the specific action by which a conflict should be resolved (e.g., "descend to flight level 70").
History
The main impetus toward the development of CTAS has been the loss of capacity in airport arrival and landings. Limitations in prediction of trajectories and weather have led to spaces on the final approaches that are not occupied by an aircraft, thus creating delays or not meeting the actual capabilities of an airport's true capacity.
In the 1980s, the National Aeronautics and Space Administration (NASA) and the Federal Aviation Administration Technical Center began an in-house research and development project to develop the software tools for achieving this optimization, working closely with controllers and human factors professionals to create a fielded system. During the mid-1990s, this system has received several field tests at Dallas-Fort Worth International Airport and at the Denver airport and center. It is also being installed at Schiphol Airport in Amsterdam, the Netherlands.
Human Factors Implementation
Human factors has played a relatively important role in the maturation of CTAS, from concept, to laboratory prototype, to simulation, to field test. From 1992 to 1997, approximately 30,000 person hours of human factors expertise have been devoted to CTAS development and fielding. In part, the successful implementation of the human factors input was a result of the fact that the development took place at NASA laboratories, with ready access to human factors professionals and active participation of controllers in developing the specifications. The development was not under constraints related to contract delivery time or required specifications. Human factors implementation was also facilitated in part by the frequent input of controllers to the design concepts of functions at all phases and frequent human-in-the-loop evaluations at varying levels of simulation fidelity. The controller's input was filtered by human factors professionals.
Another important factor is that these evaluations (and system changes based thereon) have continued as the system is being filed tested at the Dallas and Denver facilities (Harwood et al., in press). In particular, developers realized the need for extensive input from a team of controllers at the facility, in order to tailor the system to facility-specific characteristics. The introduction process was quite time-consuming, taking place over several years. This proved necessary (and advantageous), both in order to secure inputs from controllers at all levels, and also in order for human factors professionals and engineers on the design team to thoroughly familiarize themselves with the culture and operating procedures at the Denver and Dallas-Fort Worth facilities; this, in turn, was necessary in order for the trust of the operational controllers to be gained and for the CTAS advisories to be employed successfully.
It is also important to note that the system was designed to have a minimal effect on the existing automated systems (HOST and the automated radar terminal system, ARTS) and on existing procedures. Finally, it should be stressed that CTAS is presented to controllers with the philosophy that it is an advisory aid, designed to improve their capabilities, rather than as an automation replacement. That is, nothing in CTAS qualitatively alters the way in which controllers implement their control over the aircraft.
Human Factors Issues
Cognitive Task Analysis
A cognitive task analysis reveals that CTAS supports the controller's task in three critical respects, addressing the vulnerabilities identified in the panel's Phase I report. First, its four-dimensional predictive capabilities compensate for difficulties that the unaided controller will have in predicting and visualizing the long-term (i.e., five minutes) implications of multiple, complex, speed-varying trajectories subjected to various constraints, such as fuel consumption, winds, and runway configuration.
With the current system, these limits of the unaided human constrain the flexibility of considering a variety of traffic plans. Second, its interactive planning and scheduling capabilities allow multiple solutions to be evaluated off-line, with the graphics feedback available in the time lines, to facilitate the choice of plans. Here also the system supports the workload-intensive aspects of planning, particularly prevalent when multiple plans need to be compared. Finally, CTAS, particularly the final approach spacing tool, supports the controller's ability to deal with the high workload imposed by unexpected and complex events, characterized for example by a missed approach or an unanticipated runway closure. The first and second of these tasks primarily affect the efficiency of system performance, whereas the latter appears to have direct and beneficial safety implications.
Workload
A stated objective of CTAS is that it will not increase controller workload; indeed, field tests of the system reveal that this criterion has been met (Harwood et al., in press). As noted above, CTAS has the potential to reduce workload during the "spikes" imposed by unexpected scheduling and spacing requirements due to a missed approach or closed runway. However, it is also the case that workload may be shifted somewhat with the introduction of CTAS. Relying on an added channel of display information, rather than the controller's own mental judgment, may impose an increase in visual workload. In fact, any new set of procedures (such as those associated with CTAS) would be likely to impose some transient workload increase.
Finally, although not yet reported, a tool such as CTAS does have the potential of advising maneuvers that create an airspace considerably more complex than that viewed under unaided conditions (Wyndemere, 1996). In such a case, controller monitoring and perceptual workload may be increased by the controller's effort to maintain a full level of situation awareness of the more complex airspace.
Training
The general approach to CTAS is to first provide simulation, then provide a shadowing of the real traffic off-line in the system. In the shadowing mode, CTAS elements provide the advice, and the controller can compare clearances that he or she might provide on the basis of that advice with clearances more typical of an unadvised controller and evaluate the differences. The controller can then determine the rationale behind the automated advisory. This builds confidence that the computer can provide advice to maintain separation. One might anticipate the need for some training of pilots regarding the CTAS system, not because procedures are altered, but because the nature of the clearances and instructions may be changed, relative to the more standardized, space-based approaches (i.e., using the standard terminal arrival system) in a non-CTAS facility.
Communication and Coordination
Because of the philosophy by which the traffic management advisor plans are implemented via the descent advisor and the final approach spacing tool advisories, CTAS imposes a relatively heavy communication load between operators and facilities. This is supported via digital data transfer rather than voice communications.
Furthermore, the philosophy of repeated displays across different environments supports greater communications and coordination between operators, in that these can better support a shared situation awareness of the implications of different schedules. The extent to which ground-air communications are altered by CTAS remains unclear. At least one field study of the final approach spacing tool (Harwood et al., 1997), carried out at the Dallas Airport over a 6-month period indicated that the system imposed no increase in overall communications, although the nature of the communications was altered somewhat, involving more messages pertaining to runway assignments and sequencing.
Automation Issues
CTAS is sufficiently recent in its introduction that there has not been time to identify specific human factors automation issues on the basis of operational experience (e.g., operational errors or aviation safety reporting system incidents). However, analysis of system capabilities suggests at least some of these that may surface.
Mode Errors
CTAS does contain some multimode operations. For example, with the descent advisor, controllers can choose a route intercept or a waypoint capture mode for individual aircraft, as well as one of three possible speed control modes for all aircraft. However, the system appears to be designed so that different modes are prominently displayed, and active decisions must be carried out to change modes, so that mode errors would appear to be very unlikely.
Mistrust
There would appear to be a real possibility that the advice offered by CTAS could be initially mistrusted by controllers if it differed substantially from the way in which control is typically accomplished. It would seem that such trust must be carefully built through careful training with both simulated and live traffic. Indeed, Harwood et al. (in press) noted the increase in controller confidence after they had used the system (and relied on the final approach spacing tool advice) with live traffic. This provided the opportunity to see the real improvement in traffic flow (13 percent) that was achieved.
Overtrust and Complacency
Currently, the philosophy of system implementation safeguards against undue complacency. This is because controllers must still give the actual clearances orally, as they would in a nonaided situation. Hence, they remain more likely to actively think about those clearances, for example, than they would in a system in which clearances could be relayed via data link with a simple keystroke. Complacency is not generally recognized as a concern until an incident of automation failure occurs, in which the human's failure to intervene or resume control appropriately is attributed to such complacency. No such incidents have been observed with CTAS. The advice-giving algorithms were thoroughly tested, and in operational trials have yet to fail; alternatively, if inappropriate advice was ever provided, controllers were sufficiently noncomplacent that they chose to ignore it. In short, the system has been in use for an insufficient time for trust to reach the possible excessive level at which it could be described as complacency.
Past experience with other systems indicates that systems can fail, in ways that cannot be foreseen in advance (e.g., the software does not anticipate a particular unusual circumstance). Furthermore, despite the design philosophy that appears to keep the controller a relatively active participant in the control loop, it is also the case that the primary objective of CTAS is to increase the efficiency (and therefore saturation) of the terminal airspace. Such a circumstance would make recovery more difficult, should problems emerge for which CTAS would be unable to offer reliable advice.
Skill Degradation
As with complacency, so with skill degradation: CTAS has not been used long enough to determine whether this is an issue. Yet it is easy to imagine circumstances in which controllers increasingly begin to rely on CTAS advice, relaying this as instructions to pilots, losing the skills at selecting maneuvers on their own. This may be more problematic still, to the extent that the maneuvers recommended by CTAS are qualitatively different from those that would previously have been issued by unaided controllers. At this time, a clear tabulation of maneuver differences with and without CTAS has not been carried out.
Organization
The organizational implications of CTAS remain uncertain. A strength of the system is that it is designed to be advisory only; by not directly affecting required procedures, the negative impact on organizational functioning should be minimized. However, it is possible that subtle shifts in authority from the R-side controller to the D-side (who is more likely to have direct access to CTAS advisories) could have unpredictable consequences. We explore these consequences further in the discussion of conflict probes in the following section.
Conclusion
CTAS appears to be a well-conceived automation concept, addressing a valid concern of the less automated system and designed with an appropriate philosophy that is based on automated advice-giving, rather than automation-based control. As such it is characterized by a relatively low point on the level of automation action scale, which accordingly diminishes (but does not eliminate) the extent of concern for complacency. Finally, CTAS has been developed and introduced gradually, in a manner sensitive to human factors issues, and to the importance of filtered controller input into the functioning of the system. Careful human factors monitoring of the system's field use should be continued.
Conflict Probe and Interactive Planning
The core of the controller's job is to maintain a continuous flow of air traffic while also preserving adequate separation. There are three interrelated automation functionalities that can potentially assist in these goals: conflict probes, interactive planning tools, and conflict resolution advisors. The conflict probe is essentially a preview of the current flight trajectory of a given aircraft, to assess whether it will create a loss of separation with another aircraft at some time in the future. Current probes exist in the ARTS and HOST computer systems, yielding alerts if conflicts are predicted. Similar conflict probe logic also characterizes the TCAS system. These current air traffic control probes are not sophisticated, in the sense that their predictive logic is based on an extrapolation of the current ground velocity (or, in the case of TCAS, the rate of closure). They may also be described as tactical, in that they forecast only a short duration (i.e., a few minutes or less) into the future.
In contrast, however, far more intelligent probes, such as those embedded in CTAS, can include models of different aircraft capabilities, head winds, and even flight plans, to more accurately estimate the future four-dimensional trajectory of the aircraft. Smart probes, such as those incorporated into CTAS and COMPAS are far more strategic in nature, allowing much longer look-aheads. It should be noted, however, that, although systems such as COMPAS and CTAS are highly sophisticated conflict resolution systems, they leave the final authority for implementing that resolution squarely with the human. Some other development efforts over the years (e.g., the U.S. AERA system, the European ARC2000 developed by Eurocontrol) have not always embraced the same approach and have investigated the potential for fully automated conflict resolution. The ARC2000 program, for example, sought to develop a fully automated strategic resolution system. Although the development of efficient conflict resolution algorithms proved somewhat difficult, the ARC2000 is directly credited with the development of later PHARE tools (such as the PHARE HIPS, described below).
Any conflict probe is by definition based on a prediction of future behavior of the aircraft involved. Such prediction or intent inferencing must of necessity be imperfect, and it will be more so, the farther into the future that behavior is predicted. Hence, a conflict probe should be able to differentiate most likely scenarios from worst-case scenarios, the former being defined by the best guess on future behavior, and the latter being defined by the margins of uncertainty if the two aircraft maneuver toward a conflict. This uncertainty can either be portrayed graphically and continuously over time, or discretely, at a given time horizon (often selected as 20 minutes).
Once a conflict is probed and identified, it must then be negotiated. Automation has the capability of providing two further services to assist with this negotiation. Computers can recommend a course of action to resolve the conflict (automated conflict resolution), or they can provide interactive graphical tools as a decision aid, to assist controllers in developing a solution themselves to resolve the conflict.
Using the framework presented at the beginning, we note that conflict resolution is a higher level of automation than tool-based decision aiding. Ironically, however, air traffic control has proceeded more directly to implementing conflict resolution than to providing interactive tools for decision aiding. For example, we note that CTAS and COMPAS both employ automation to formulate recommended solutions for the controller to either accept (and implement through traditional procedures) or reject, and both are in active service at certain airports (Frankfurt, Denver, Dallas-Fort Worth). A less mature level of development characterizes interactive decision aids, two of which we describe in some detail below: the user request evaluation tool developed for use in the United States and the highly interactive problem solver (HIPS) developed by Eurocontrol.
User Request Evaluation Tool
Functionality
The user request evaluation tool (URET), developed by the MITRE Corporation for assistance to the en route controller, provides a conflict probe based on a 20-minute look-ahead capability. The probe is a "smart" one, accounting for different flight plans, aircraft models (i.e., flight capabilities), and anticipated head winds, in determining the best estimate of each aircraft's position 20 minutes into the future. (It does not, however, take into account any future flight plans based on scheduled mode changes in a flight management system).
The results of the probe are displayed to the D-side controller in two modes: a graphic mode portrays the flight path on a large-scale electronic map. Projected flight paths are color-coded: a red code indicates a likely future conflict, and an amber code indicates a possible conflict. The latter represents a wider bound of uncertainty of future behavior. A tabular mode, visible concurrently, characterizes each aircraft by a line of text portraying flight information; it will also color-code any pair of aircraft involved in a predicted conflict.
The key interactive feature of the user request evaluation tool is the planning mode, which allows the D-side controller to play what-if scenarios by graphically examining the implications of alternative instructions that could be given to one or both aircraft. Thus, for example, a controller might see that a current predicted conflict can be eliminated by increasing the air speed of one of the aircraft by 30 knots. The recommended change can then be suggested to the R-side controller, who may then choose to implement the instructions. Clear and salient indications are provided on the display to show that it is in the planning mode (i.e., that changed flight paths have not actually been provided to the aircraft in question).
Human Factors Implementation
As developed at the MITRE Corporation, the user request evaluation tool received a substantial amount of input from controllers in specifying both functionality and the interface, and such input was guided by human factors professionals. Equally important, current field tests, now under way at the Indianapolis Center, are being closely monitored by human factors personnel to evaluate both strengths and deficiencies of the system in operational use.
The field evaluation at Indianapolis was preceded by providing four teams of three controllers with 16 hours of training on the system. A series of tests were then carried out, with R-side and D-side controllers advised by the third controller on the team working with the user request evaluation tool. The study revealed that the tool was positively evaluated by the controllers, and all felt that it could be easily used by the D-side controller. Use of the tool resulted in fewer maneuvers instructed to the aircraft with no loss of separation and greater efficiency. This difference resulted because the longer (and more accurate) look-ahead capability of the user request evaluation tool would often reveal that current trajectories were conflict free, whereas the unaided controller, behaving conservatively, might judge that the same trajectories could generate a conflict and hence instruct a maneuver. In this regard, the user request evaluation tool nicely supported and augmented the predictive capabilities of the human controller.
A second, less expected observed benefit was that the user request evaluation tool enabled controllers to more efficiently assess pilot requests for preferred routes and deviations, since a quick interaction with the planning aid could determine if such a request was conflict free.
Programme for Harmonised Air Traffic Management Research in Eurocontrol Demonstration Tool Set
In Europe, PHARE (Programme for Harmonised Air Traffic Management Research in Eurocontrol) is developing a research set of integrated tools, designed to assist the controller in determining and ensuring conflict-free and efficient trajectories. The system is based on a concept of closed-loop four-dimensional trajectory negotiation and control, whereby sophisticated air and ground systems can negotiate a suitable trajectory, and an airborne flight management system can issue appropriate clearances to track the agreed trajectory (Maignan, 1994). Principal developments of PHARE include an experimental flight management system, advanced data link capability, and a set of advanced controller tools. A phased development of the PHARE demonstration tool set is taking place, with the three consecutive phases focusing on en route, terminal, and multisector operations, respectively. Among the core set of PHARE automation tools (as embodied in the en route interface) is the highly interactive problem solver (HIPS), which is increasingly referred to as the PHARE Advanced Tools (PATS) Problem Solver.
Functionality
The highly interactive problem solver is a sophisticated interface tool that permits the controller to view, edit, negotiate, and approve trajectories (National Air Traffic Services, 1996). The other PHARE advanced tools are not directly visible to the controller; instead, he or she interacts with these other tools through the HIPS interface. HIPS takes the form of both profile and plan view display windows, in which time-related conflict regions are graphically represented as "blobs" that the controller must separate. A controller can use HIPS to assess a trajectory, generate an alternative clearance, or modify an existing clearance (via altitude, heading, or speed modifications).
The developmental PHARE en route interface, including the HIPS. When the flight path monitoring algorithm predicts a loss of separation between two (or more) aircraft, the HIPS display presents the time-weighted (four-dimensional) conflict zones as red regions (potential conflict regions are color-coded yellow). A loss of separation occurs whenever an aircraft's predicted trajectory passes through any region of potential conflict, known as nogo zones or, more commonly, blobs. Using HIPS, the controller is then able to implement prospective solutions using one of three possible maneuver spaces (altitude, speed, or heading). Resolving the conflict thus involves mouse-dragging aircraft in one of the maneuver windows, so as to physically separate red blobs, which in turn (once the solution is accepted) triggers the issuance of an appropriate clearance.
Since controllers are free to implement solutions in any maneuver space, the HIPS concept permits alternative control strategies. Furthermore, it provides salient and immediate feedback on the utility of various strategies. For example, a controller can compare the efficiency of a heading-versus speed-based solution, before actually implementing either.
Human Factors Implementation
Human factors considerations appear to have been paramount at all stages of the HIPS development (Jorna, 1997). Although elements of the system were inspired by the earlier ARC2000 European prototype system, unlike its predecessor HIPS does not implement automatic conflict resolution.
Instead, HIPS is explicitly based on a human-centered approach and, like the user request evaluation tool described above, tries to keep the controller in the loop by restructuring the data in a way that facilitates strategic air traffic management decisions. Under HIPS, such decisions remain very much the domain of the air traffic controller.
Empirical trials of the initial PHARE en route system were carried out during late 1995 in the United Kingdom, using 32 active controllers from eight different European air traffic control organizations. The trials were aimed at evaluating the effects of both the PHARE advanced tool set and the presence of advanced (4-D-capable, data link-equipped) aircraft, in terms of controller workload, traffic throughput, and situation awareness.
Subjective workload data suggest that the PHARE advanced tools may beneficially redistribute workload between the tactical and the planning controller (under baseline conditions, reported workload had been higher for the tactical than for the planning controller), albeit at the cost of higher total team workload. Survey data revealed that, overall, controllers were very positive about the display aspects of the PHARE system. Although controllers gave the advanced tools mixed reviews in general, they were extremely enthusiastic about HIPS.
In terms of flight efficiency, the full PHARE scenario (advanced tools combined with advanced aircraft capability) yielded better flight-level-request performance (that is, aircraft spent a significantly greater percentage of time at or near their requested flight level) than either the baseline or the advanced tools condition. The data did not, however, reveal hypothesized situation awareness benefits.
Automation IssuesLike other advanced or proposed automation concepts, conflict probes and interactive problem-solving tools are sufficiently recent that major problems have not yet had a chance to surface. Nevertheless, extrapolating from other systems, we can identify certain potential sources of problems.
New Error Forms: Mode Errors
These systems appear to have been designed to be relatively simple, with few modes to invite confusion. For the user request evaluation tool, a concern is whether the portrayal of flight paths in the planning mode could become confused with its portrayal in the active traffic mode.
To guard against this, both it and the highly interactive problem solver employ salient color-coding (e.g., of adjacent sectors under HIPS). In addition to color-coding, HIPS also guards against team mode confusion through different displays for the planning and the tactical controllers. The planning controller can work in either look-ahead or real-time mode (and therefore has no radiotelephony communication capability), whereas the tactical controller's display operates only in real time.
Workload and Situation Awareness
By providing visual representations of future flight paths, tools such as the user request evaluation tool and the highly interactive problem solver should serve to increase situation awareness and reduce the workload of planning, which conventionally must be done on a cognitive basis by interpreting and mentally visualizing digital information (i.e., from flight strips). In this sense, as long as the planning tool remains within the domain of the D-side controller, workload may be reduced. Should, however, the R-side controller begin to shift attention to the user request evaluation tool to or the highly interactive problem solver display, one can envision negative workload implications, to the extent that visual resources are removed from the plan view display.
Also, it is possible that R-side situation awareness could degrade if the controller adopts a strategy of automatically accepting recommendations based on the tool, without carefully thinking through the implications of those suggestions. Finally, an indirect negative effect on workload could result if the planning tools are used extensively to divert aircraft from FAA-preferred routes to user-preferred routes in order to expedite flying. The resulting increase of complexity in the traffic pattern will negatively affect both perceptual workload and situation awareness, as documented by recent studies.
Mistrust
Adequate trust in the systems can and should be developed by careful training, as has been undertaken in the field tests at Indianapolis and advised on the basis of work with HIPS. The algorithms and assumptions of conflict probe devices should be consistent with the controller's means of prediction and the controller's mental model.
Excessive false alarm rates for conflict alerts, a source of user mistrust, have been addressed in the user request evaluation tool by the philosophy of providing two levels of alert (amber and red), which implicitly characterize the automation's uncertainty of future traffic behavior. This bilevel or ''likelihood alarm" philosophy has been shown to be a useful remediation to problems of mistrust resulting from false alarms.
Overtrust and Complacency
The impacts of complacency and overtrust remain to be determined. This is because such states are not of operational concern until automation fails, and as yet there have been no documented instances of tool failure. (It is important to note here that, in the development of the tools, there was no apparent effort to develop a fault tree analysis of the possible causes and consequences of such low-probability events). A key feature of both the user request evaluation tool and the highly interactive problem solver is to keep the controller actively involved in the problem-solving and decision formulations.
Hence, there is no likelihood of overtrusting automated solutions (which may be in error), since automation is not involved in recommending the solutions. (This, of course, is in contrast to the conflict resolution tools, discussed in the context of CTAS.) One important issue related to trust concerns the extent to which the intelligence within an interactive planning tool may not be cognizant of other hazard information (e.g., weather) that a controller normally considers.
Skill Degradation
As with overtrust and complacency, discussed in the previous section, skill degradation does not appear to present an issue. Controllers will continue to practice their skills in constructing conflict-free trajectories, but they will be better supported with graphical tools to implement those skills. Indeed, an argument can be made that such a tool will improve skill development by providing real-time feedback.
For instance, en route controllers tend to achieve separation through either vertical (flight level) or direction (heading) control. In part this tendency derives from the small speed envelope of cruising jets and the resulting limited utility of speed control in en route airspace. Because the effects of speed manipulations become apparent only gradually, they can be difficult for the controller to visualize. As a result, the feedback provided by graphical look-ahead tools may enable the controller to develop better speed control skills.
Communication and Coordination
Both the user request evaluation tool and the highly interactive problem solver are designed to support more long-range strategic planning. As such, they have the potential to shift more control from the R-side to the D-side. Indeed, one can envision a scenario in which the R-side controller has little to do but implement long-range suggestions made by the tool-supported D-side controller, there-by guaranteeing conflict-free flights, with little need for active controlling. Hence, while the controller team may not suffer a loss of skills, there may well be a transference of skills from one controller to another within the team.
A second coordination issue emanating from the strategic, long-term nature of these interactive tools may be an increased need for coordination between sectors, since it seems more likely that aircraft will be maneuvered either on the basis of implications of an aircraft in a different sector, or in a manner that will affect that aircraft when it enters a different sector. A controller in one sector may then need to be increasingly vigilant of the behavior of controllers in adjacent sectors who are using the user request evaluation tool.
Failure Recovery
The prime issues for failure recovery are twofold, both emanating from potential problems identified above.
First, it is possible to envision a scenario in which the deployment of interactive tools has enabled more complex (and possibly more densely packed) traffic flow.
Second, this scenario situation has also left the R-side controller with reduced situation awareness of the current airspace (because trajectory changes were not imposed by his own decisions). A sudden failure of the user request evaluation tool or conflict probe system could thereby leave the R-side controller more vulnerable in issuing the rapid tactical commands necessary to avoid conflict situations.
User Acceptance
As with many sophisticated forms of automation, if systems like these are not carefully designed and introduced with adequate concern for controller training, the potential exists for limited user acceptance to threaten job satisfaction, which may in turn be reflected in perceived job insecurity. The more capable such automated systems are, the more likely such fears become. Furthermore, history suggests that such fears are not always unwarranted; in 1982, the FAA's modernization plans were presented to the U.S. Congress with the promise that they would reduce future staffing requirements. Some also fear that advanced air traffic control automation, if not well designed, may erode the job satisfaction a controller derives from resolving a challenging situation.
Conclusion
Interactive planning tools appear to offer many of the benefits of automated information collection and integration (providing more easily visualizable predictive information to support human problem solving), without inviting some of the most obvious costs associated with automation of response (complacency and skill degradation). Nevertheless, predicted effects, discussed above, remain uncertain and should be the focus of continued evaluation.
The interface for the COMPAS presents the controller with a sequencing time line, with arrivals ordered from latest to earliest, top to bottom. The time associated with each aircraft represents the estimated arrival time, over either the metering fix (in the case of the en route controller) or the approach gate (for the approach controller). Aircraft weight class and approach direction are represented in the display. The control advisories themselves are presented as one of four possible characters beside the aircraft label: X to expedite up to two minutes, O for no action, R for delay up to four minutes, and H to hold for more than four minutes.
Operational experience with COMPAS has demonstrated reductions in planning and coordination workload, as well as reductions in the time spent on coordination and smoothing of the traffic flow in the terminal area.
Notice that COMPAS provides general resolution advisories (e.g., ''hold for more than four minutes"); the descent advisor of CTAS provides another level of assistancenamely, the specific action by which a conflict should be resolved (e.g., "descend to flight level 70").
History
The main impetus toward the development of CTAS has been the loss of capacity in airport arrival and landings. Limitations in prediction of trajectories and weather have led to spaces on the final approaches that are not occupied by an aircraft, thus creating delays or not meeting the actual capabilities of an airport's true capacity.
In the 1980s, the National Aeronautics and Space Administration (NASA) and the Federal Aviation Administration Technical Center began an in-house research and development project to develop the software tools for achieving this optimization, working closely with controllers and human factors professionals to create a fielded system. During the mid-1990s, this system has received several field tests at Dallas-Fort Worth International Airport and at the Denver airport and center. It is also being installed at Schiphol Airport in Amsterdam, the Netherlands.
Human Factors Implementation
Human factors has played a relatively important role in the maturation of CTAS, from concept, to laboratory prototype, to simulation, to field test. From 1992 to 1997, approximately 30,000 person hours of human factors expertise have been devoted to CTAS development and fielding. In part, the successful implementation of the human factors input was a result of the fact that the development took place at NASA laboratories, with ready access to human factors professionals and active participation of controllers in developing the specifications. The development was not under constraints related to contract delivery time or required specifications. Human factors implementation was also facilitated in part by the frequent input of controllers to the design concepts of functions at all phases and frequent human-in-the-loop evaluations at varying levels of simulation fidelity. The controller's input was filtered by human factors professionals.
Another important factor is that these evaluations (and system changes based thereon) have continued as the system is being filed tested at the Dallas and Denver facilities (Harwood et al., in press). In particular, developers realized the need for extensive input from a team of controllers at the facility, in order to tailor the system to facility-specific characteristics. The introduction process was quite time-consuming, taking place over several years. This proved necessary (and advantageous), both in order to secure inputs from controllers at all levels, and also in order for human factors professionals and engineers on the design team to thoroughly familiarize themselves with the culture and operating procedures at the Denver and Dallas-Fort Worth facilities; this, in turn, was necessary in order for the trust of the operational controllers to be gained and for the CTAS advisories to be employed successfully.
It is also important to note that the system was designed to have a minimal effect on the existing automated systems (HOST and the automated radar terminal system, ARTS) and on existing procedures. Finally, it should be stressed that CTAS is presented to controllers with the philosophy that it is an advisory aid, designed to improve their capabilities, rather than as an automation replacement. That is, nothing in CTAS qualitatively alters the way in which controllers implement their control over the aircraft.
Human Factors Issues
Cognitive Task Analysis
A cognitive task analysis reveals that CTAS supports the controller's task in three critical respects, addressing the vulnerabilities identified in the panel's Phase I report. First, its four-dimensional predictive capabilities compensate for difficulties that the unaided controller will have in predicting and visualizing the long-term (i.e., five minutes) implications of multiple, complex, speed-varying trajectories subjected to various constraints, such as fuel consumption, winds, and runway configuration.
With the current system, these limits of the unaided human constrain the flexibility of considering a variety of traffic plans. Second, its interactive planning and scheduling capabilities allow multiple solutions to be evaluated off-line, with the graphics feedback available in the time lines, to facilitate the choice of plans. Here also the system supports the workload-intensive aspects of planning, particularly prevalent when multiple plans need to be compared. Finally, CTAS, particularly the final approach spacing tool, supports the controller's ability to deal with the high workload imposed by unexpected and complex events, characterized for example by a missed approach or an unanticipated runway closure. The first and second of these tasks primarily affect the efficiency of system performance, whereas the latter appears to have direct and beneficial safety implications.
Workload
A stated objective of CTAS is that it will not increase controller workload; indeed, field tests of the system reveal that this criterion has been met (Harwood et al., in press). As noted above, CTAS has the potential to reduce workload during the "spikes" imposed by unexpected scheduling and spacing requirements due to a missed approach or closed runway. However, it is also the case that workload may be shifted somewhat with the introduction of CTAS. Relying on an added channel of display information, rather than the controller's own mental judgment, may impose an increase in visual workload. In fact, any new set of procedures (such as those associated with CTAS) would be likely to impose some transient workload increase.
Finally, although not yet reported, a tool such as CTAS does have the potential of advising maneuvers that create an airspace considerably more complex than that viewed under unaided conditions (Wyndemere, 1996). In such a case, controller monitoring and perceptual workload may be increased by the controller's effort to maintain a full level of situation awareness of the more complex airspace.
Training
The general approach to CTAS is to first provide simulation, then provide a shadowing of the real traffic off-line in the system. In the shadowing mode, CTAS elements provide the advice, and the controller can compare clearances that he or she might provide on the basis of that advice with clearances more typical of an unadvised controller and evaluate the differences. The controller can then determine the rationale behind the automated advisory. This builds confidence that the computer can provide advice to maintain separation. One might anticipate the need for some training of pilots regarding the CTAS system, not because procedures are altered, but because the nature of the clearances and instructions may be changed, relative to the more standardized, space-based approaches (i.e., using the standard terminal arrival system) in a non-CTAS facility.
Communication and Coordination
Because of the philosophy by which the traffic management advisor plans are implemented via the descent advisor and the final approach spacing tool advisories, CTAS imposes a relatively heavy communication load between operators and facilities. This is supported via digital data transfer rather than voice communications.
Furthermore, the philosophy of repeated displays across different environments supports greater communications and coordination between operators, in that these can better support a shared situation awareness of the implications of different schedules. The extent to which ground-air communications are altered by CTAS remains unclear. At least one field study of the final approach spacing tool (Harwood et al., 1997), carried out at the Dallas Airport over a 6-month period indicated that the system imposed no increase in overall communications, although the nature of the communications was altered somewhat, involving more messages pertaining to runway assignments and sequencing.
Automation Issues
CTAS is sufficiently recent in its introduction that there has not been time to identify specific human factors automation issues on the basis of operational experience (e.g., operational errors or aviation safety reporting system incidents). However, analysis of system capabilities suggests at least some of these that may surface.
Mode Errors
CTAS does contain some multimode operations. For example, with the descent advisor, controllers can choose a route intercept or a waypoint capture mode for individual aircraft, as well as one of three possible speed control modes for all aircraft. However, the system appears to be designed so that different modes are prominently displayed, and active decisions must be carried out to change modes, so that mode errors would appear to be very unlikely.
Mistrust
There would appear to be a real possibility that the advice offered by CTAS could be initially mistrusted by controllers if it differed substantially from the way in which control is typically accomplished. It would seem that such trust must be carefully built through careful training with both simulated and live traffic. Indeed, Harwood et al. (in press) noted the increase in controller confidence after they had used the system (and relied on the final approach spacing tool advice) with live traffic. This provided the opportunity to see the real improvement in traffic flow (13 percent) that was achieved.
Overtrust and Complacency
Currently, the philosophy of system implementation safeguards against undue complacency. This is because controllers must still give the actual clearances orally, as they would in a nonaided situation. Hence, they remain more likely to actively think about those clearances, for example, than they would in a system in which clearances could be relayed via data link with a simple keystroke. Complacency is not generally recognized as a concern until an incident of automation failure occurs, in which the human's failure to intervene or resume control appropriately is attributed to such complacency. No such incidents have been observed with CTAS. The advice-giving algorithms were thoroughly tested, and in operational trials have yet to fail; alternatively, if inappropriate advice was ever provided, controllers were sufficiently noncomplacent that they chose to ignore it. In short, the system has been in use for an insufficient time for trust to reach the possible excessive level at which it could be described as complacency.
Past experience with other systems indicates that systems can fail, in ways that cannot be foreseen in advance (e.g., the software does not anticipate a particular unusual circumstance). Furthermore, despite the design philosophy that appears to keep the controller a relatively active participant in the control loop, it is also the case that the primary objective of CTAS is to increase the efficiency (and therefore saturation) of the terminal airspace. Such a circumstance would make recovery more difficult, should problems emerge for which CTAS would be unable to offer reliable advice.
Skill Degradation
As with complacency, so with skill degradation: CTAS has not been used long enough to determine whether this is an issue. Yet it is easy to imagine circumstances in which controllers increasingly begin to rely on CTAS advice, relaying this as instructions to pilots, losing the skills at selecting maneuvers on their own. This may be more problematic still, to the extent that the maneuvers recommended by CTAS are qualitatively different from those that would previously have been issued by unaided controllers. At this time, a clear tabulation of maneuver differences with and without CTAS has not been carried out.
Organization
The organizational implications of CTAS remain uncertain. A strength of the system is that it is designed to be advisory only; by not directly affecting required procedures, the negative impact on organizational functioning should be minimized. However, it is possible that subtle shifts in authority from the R-side controller to the D-side (who is more likely to have direct access to CTAS advisories) could have unpredictable consequences. We explore these consequences further in the discussion of conflict probes in the following section.
Conclusion
CTAS appears to be a well-conceived automation concept, addressing a valid concern of the less automated system and designed with an appropriate philosophy that is based on automated advice-giving, rather than automation-based control. As such it is characterized by a relatively low point on the level of automation action scale, which accordingly diminishes (but does not eliminate) the extent of concern for complacency. Finally, CTAS has been developed and introduced gradually, in a manner sensitive to human factors issues, and to the importance of filtered controller input into the functioning of the system. Careful human factors monitoring of the system's field use should be continued.
Conflict Probe and Interactive Planning
The core of the controller's job is to maintain a continuous flow of air traffic while also preserving adequate separation. There are three interrelated automation functionalities that can potentially assist in these goals: conflict probes, interactive planning tools, and conflict resolution advisors. The conflict probe is essentially a preview of the current flight trajectory of a given aircraft, to assess whether it will create a loss of separation with another aircraft at some time in the future. Current probes exist in the ARTS and HOST computer systems, yielding alerts if conflicts are predicted. Similar conflict probe logic also characterizes the TCAS system. These current air traffic control probes are not sophisticated, in the sense that their predictive logic is based on an extrapolation of the current ground velocity (or, in the case of TCAS, the rate of closure). They may also be described as tactical, in that they forecast only a short duration (i.e., a few minutes or less) into the future.
In contrast, however, far more intelligent probes, such as those embedded in CTAS, can include models of different aircraft capabilities, head winds, and even flight plans, to more accurately estimate the future four-dimensional trajectory of the aircraft. Smart probes, such as those incorporated into CTAS and COMPAS are far more strategic in nature, allowing much longer look-aheads. It should be noted, however, that, although systems such as COMPAS and CTAS are highly sophisticated conflict resolution systems, they leave the final authority for implementing that resolution squarely with the human. Some other development efforts over the years (e.g., the U.S. AERA system, the European ARC2000 developed by Eurocontrol) have not always embraced the same approach and have investigated the potential for fully automated conflict resolution. The ARC2000 program, for example, sought to develop a fully automated strategic resolution system. Although the development of efficient conflict resolution algorithms proved somewhat difficult, the ARC2000 is directly credited with the development of later PHARE tools (such as the PHARE HIPS, described below).
Any conflict probe is by definition based on a prediction of future behavior of the aircraft involved. Such prediction or intent inferencing must of necessity be imperfect, and it will be more so, the farther into the future that behavior is predicted. Hence, a conflict probe should be able to differentiate most likely scenarios from worst-case scenarios, the former being defined by the best guess on future behavior, and the latter being defined by the margins of uncertainty if the two aircraft maneuver toward a conflict. This uncertainty can either be portrayed graphically and continuously over time, or discretely, at a given time horizon (often selected as 20 minutes).
Once a conflict is probed and identified, it must then be negotiated. Automation has the capability of providing two further services to assist with this negotiation. Computers can recommend a course of action to resolve the conflict (automated conflict resolution), or they can provide interactive graphical tools as a decision aid, to assist controllers in developing a solution themselves to resolve the conflict.
Using the framework presented at the beginning, we note that conflict resolution is a higher level of automation than tool-based decision aiding. Ironically, however, air traffic control has proceeded more directly to implementing conflict resolution than to providing interactive tools for decision aiding. For example, we note that CTAS and COMPAS both employ automation to formulate recommended solutions for the controller to either accept (and implement through traditional procedures) or reject, and both are in active service at certain airports (Frankfurt, Denver, Dallas-Fort Worth). A less mature level of development characterizes interactive decision aids, two of which we describe in some detail below: the user request evaluation tool developed for use in the United States and the highly interactive problem solver (HIPS) developed by Eurocontrol.
User Request Evaluation Tool
Functionality
The user request evaluation tool (URET), developed by the MITRE Corporation for assistance to the en route controller, provides a conflict probe based on a 20-minute look-ahead capability. The probe is a "smart" one, accounting for different flight plans, aircraft models (i.e., flight capabilities), and anticipated head winds, in determining the best estimate of each aircraft's position 20 minutes into the future. (It does not, however, take into account any future flight plans based on scheduled mode changes in a flight management system).
The results of the probe are displayed to the D-side controller in two modes: a graphic mode portrays the flight path on a large-scale electronic map. Projected flight paths are color-coded: a red code indicates a likely future conflict, and an amber code indicates a possible conflict. The latter represents a wider bound of uncertainty of future behavior. A tabular mode, visible concurrently, characterizes each aircraft by a line of text portraying flight information; it will also color-code any pair of aircraft involved in a predicted conflict.
The key interactive feature of the user request evaluation tool is the planning mode, which allows the D-side controller to play what-if scenarios by graphically examining the implications of alternative instructions that could be given to one or both aircraft. Thus, for example, a controller might see that a current predicted conflict can be eliminated by increasing the air speed of one of the aircraft by 30 knots. The recommended change can then be suggested to the R-side controller, who may then choose to implement the instructions. Clear and salient indications are provided on the display to show that it is in the planning mode (i.e., that changed flight paths have not actually been provided to the aircraft in question).
Human Factors Implementation
As developed at the MITRE Corporation, the user request evaluation tool received a substantial amount of input from controllers in specifying both functionality and the interface, and such input was guided by human factors professionals. Equally important, current field tests, now under way at the Indianapolis Center, are being closely monitored by human factors personnel to evaluate both strengths and deficiencies of the system in operational use.
The field evaluation at Indianapolis was preceded by providing four teams of three controllers with 16 hours of training on the system. A series of tests were then carried out, with R-side and D-side controllers advised by the third controller on the team working with the user request evaluation tool. The study revealed that the tool was positively evaluated by the controllers, and all felt that it could be easily used by the D-side controller. Use of the tool resulted in fewer maneuvers instructed to the aircraft with no loss of separation and greater efficiency. This difference resulted because the longer (and more accurate) look-ahead capability of the user request evaluation tool would often reveal that current trajectories were conflict free, whereas the unaided controller, behaving conservatively, might judge that the same trajectories could generate a conflict and hence instruct a maneuver. In this regard, the user request evaluation tool nicely supported and augmented the predictive capabilities of the human controller.
A second, less expected observed benefit was that the user request evaluation tool enabled controllers to more efficiently assess pilot requests for preferred routes and deviations, since a quick interaction with the planning aid could determine if such a request was conflict free.
Programme for Harmonised Air Traffic Management Research in Eurocontrol Demonstration Tool Set
In Europe, PHARE (Programme for Harmonised Air Traffic Management Research in Eurocontrol) is developing a research set of integrated tools, designed to assist the controller in determining and ensuring conflict-free and efficient trajectories. The system is based on a concept of closed-loop four-dimensional trajectory negotiation and control, whereby sophisticated air and ground systems can negotiate a suitable trajectory, and an airborne flight management system can issue appropriate clearances to track the agreed trajectory (Maignan, 1994). Principal developments of PHARE include an experimental flight management system, advanced data link capability, and a set of advanced controller tools. A phased development of the PHARE demonstration tool set is taking place, with the three consecutive phases focusing on en route, terminal, and multisector operations, respectively. Among the core set of PHARE automation tools (as embodied in the en route interface) is the highly interactive problem solver (HIPS), which is increasingly referred to as the PHARE Advanced Tools (PATS) Problem Solver.
Functionality
The highly interactive problem solver is a sophisticated interface tool that permits the controller to view, edit, negotiate, and approve trajectories (National Air Traffic Services, 1996). The other PHARE advanced tools are not directly visible to the controller; instead, he or she interacts with these other tools through the HIPS interface. HIPS takes the form of both profile and plan view display windows, in which time-related conflict regions are graphically represented as "blobs" that the controller must separate. A controller can use HIPS to assess a trajectory, generate an alternative clearance, or modify an existing clearance (via altitude, heading, or speed modifications).
The developmental PHARE en route interface, including the HIPS. When the flight path monitoring algorithm predicts a loss of separation between two (or more) aircraft, the HIPS display presents the time-weighted (four-dimensional) conflict zones as red regions (potential conflict regions are color-coded yellow). A loss of separation occurs whenever an aircraft's predicted trajectory passes through any region of potential conflict, known as nogo zones or, more commonly, blobs. Using HIPS, the controller is then able to implement prospective solutions using one of three possible maneuver spaces (altitude, speed, or heading). Resolving the conflict thus involves mouse-dragging aircraft in one of the maneuver windows, so as to physically separate red blobs, which in turn (once the solution is accepted) triggers the issuance of an appropriate clearance.
Since controllers are free to implement solutions in any maneuver space, the HIPS concept permits alternative control strategies. Furthermore, it provides salient and immediate feedback on the utility of various strategies. For example, a controller can compare the efficiency of a heading-versus speed-based solution, before actually implementing either.
Human Factors Implementation
Human factors considerations appear to have been paramount at all stages of the HIPS development (Jorna, 1997). Although elements of the system were inspired by the earlier ARC2000 European prototype system, unlike its predecessor HIPS does not implement automatic conflict resolution.
Instead, HIPS is explicitly based on a human-centered approach and, like the user request evaluation tool described above, tries to keep the controller in the loop by restructuring the data in a way that facilitates strategic air traffic management decisions. Under HIPS, such decisions remain very much the domain of the air traffic controller.
Empirical trials of the initial PHARE en route system were carried out during late 1995 in the United Kingdom, using 32 active controllers from eight different European air traffic control organizations. The trials were aimed at evaluating the effects of both the PHARE advanced tool set and the presence of advanced (4-D-capable, data link-equipped) aircraft, in terms of controller workload, traffic throughput, and situation awareness.
Subjective workload data suggest that the PHARE advanced tools may beneficially redistribute workload between the tactical and the planning controller (under baseline conditions, reported workload had been higher for the tactical than for the planning controller), albeit at the cost of higher total team workload. Survey data revealed that, overall, controllers were very positive about the display aspects of the PHARE system. Although controllers gave the advanced tools mixed reviews in general, they were extremely enthusiastic about HIPS.
In terms of flight efficiency, the full PHARE scenario (advanced tools combined with advanced aircraft capability) yielded better flight-level-request performance (that is, aircraft spent a significantly greater percentage of time at or near their requested flight level) than either the baseline or the advanced tools condition. The data did not, however, reveal hypothesized situation awareness benefits.
Automation IssuesLike other advanced or proposed automation concepts, conflict probes and interactive problem-solving tools are sufficiently recent that major problems have not yet had a chance to surface. Nevertheless, extrapolating from other systems, we can identify certain potential sources of problems.
New Error Forms: Mode Errors
These systems appear to have been designed to be relatively simple, with few modes to invite confusion. For the user request evaluation tool, a concern is whether the portrayal of flight paths in the planning mode could become confused with its portrayal in the active traffic mode.
To guard against this, both it and the highly interactive problem solver employ salient color-coding (e.g., of adjacent sectors under HIPS). In addition to color-coding, HIPS also guards against team mode confusion through different displays for the planning and the tactical controllers. The planning controller can work in either look-ahead or real-time mode (and therefore has no radiotelephony communication capability), whereas the tactical controller's display operates only in real time.
Workload and Situation Awareness
By providing visual representations of future flight paths, tools such as the user request evaluation tool and the highly interactive problem solver should serve to increase situation awareness and reduce the workload of planning, which conventionally must be done on a cognitive basis by interpreting and mentally visualizing digital information (i.e., from flight strips). In this sense, as long as the planning tool remains within the domain of the D-side controller, workload may be reduced. Should, however, the R-side controller begin to shift attention to the user request evaluation tool to or the highly interactive problem solver display, one can envision negative workload implications, to the extent that visual resources are removed from the plan view display.
Also, it is possible that R-side situation awareness could degrade if the controller adopts a strategy of automatically accepting recommendations based on the tool, without carefully thinking through the implications of those suggestions. Finally, an indirect negative effect on workload could result if the planning tools are used extensively to divert aircraft from FAA-preferred routes to user-preferred routes in order to expedite flying. The resulting increase of complexity in the traffic pattern will negatively affect both perceptual workload and situation awareness, as documented by recent studies.
Mistrust
Adequate trust in the systems can and should be developed by careful training, as has been undertaken in the field tests at Indianapolis and advised on the basis of work with HIPS. The algorithms and assumptions of conflict probe devices should be consistent with the controller's means of prediction and the controller's mental model.
Excessive false alarm rates for conflict alerts, a source of user mistrust, have been addressed in the user request evaluation tool by the philosophy of providing two levels of alert (amber and red), which implicitly characterize the automation's uncertainty of future traffic behavior. This bilevel or ''likelihood alarm" philosophy has been shown to be a useful remediation to problems of mistrust resulting from false alarms.
Overtrust and Complacency
The impacts of complacency and overtrust remain to be determined. This is because such states are not of operational concern until automation fails, and as yet there have been no documented instances of tool failure. (It is important to note here that, in the development of the tools, there was no apparent effort to develop a fault tree analysis of the possible causes and consequences of such low-probability events). A key feature of both the user request evaluation tool and the highly interactive problem solver is to keep the controller actively involved in the problem-solving and decision formulations.
Hence, there is no likelihood of overtrusting automated solutions (which may be in error), since automation is not involved in recommending the solutions. (This, of course, is in contrast to the conflict resolution tools, discussed in the context of CTAS.) One important issue related to trust concerns the extent to which the intelligence within an interactive planning tool may not be cognizant of other hazard information (e.g., weather) that a controller normally considers.
Skill Degradation
As with overtrust and complacency, discussed in the previous section, skill degradation does not appear to present an issue. Controllers will continue to practice their skills in constructing conflict-free trajectories, but they will be better supported with graphical tools to implement those skills. Indeed, an argument can be made that such a tool will improve skill development by providing real-time feedback.
For instance, en route controllers tend to achieve separation through either vertical (flight level) or direction (heading) control. In part this tendency derives from the small speed envelope of cruising jets and the resulting limited utility of speed control in en route airspace. Because the effects of speed manipulations become apparent only gradually, they can be difficult for the controller to visualize. As a result, the feedback provided by graphical look-ahead tools may enable the controller to develop better speed control skills.
Communication and Coordination
Both the user request evaluation tool and the highly interactive problem solver are designed to support more long-range strategic planning. As such, they have the potential to shift more control from the R-side to the D-side. Indeed, one can envision a scenario in which the R-side controller has little to do but implement long-range suggestions made by the tool-supported D-side controller, there-by guaranteeing conflict-free flights, with little need for active controlling. Hence, while the controller team may not suffer a loss of skills, there may well be a transference of skills from one controller to another within the team.
A second coordination issue emanating from the strategic, long-term nature of these interactive tools may be an increased need for coordination between sectors, since it seems more likely that aircraft will be maneuvered either on the basis of implications of an aircraft in a different sector, or in a manner that will affect that aircraft when it enters a different sector. A controller in one sector may then need to be increasingly vigilant of the behavior of controllers in adjacent sectors who are using the user request evaluation tool.
Failure Recovery
The prime issues for failure recovery are twofold, both emanating from potential problems identified above.
First, it is possible to envision a scenario in which the deployment of interactive tools has enabled more complex (and possibly more densely packed) traffic flow.
Second, this scenario situation has also left the R-side controller with reduced situation awareness of the current airspace (because trajectory changes were not imposed by his own decisions). A sudden failure of the user request evaluation tool or conflict probe system could thereby leave the R-side controller more vulnerable in issuing the rapid tactical commands necessary to avoid conflict situations.
User Acceptance
As with many sophisticated forms of automation, if systems like these are not carefully designed and introduced with adequate concern for controller training, the potential exists for limited user acceptance to threaten job satisfaction, which may in turn be reflected in perceived job insecurity. The more capable such automated systems are, the more likely such fears become. Furthermore, history suggests that such fears are not always unwarranted; in 1982, the FAA's modernization plans were presented to the U.S. Congress with the promise that they would reduce future staffing requirements. Some also fear that advanced air traffic control automation, if not well designed, may erode the job satisfaction a controller derives from resolving a challenging situation.
Conclusion
Interactive planning tools appear to offer many of the benefits of automated information collection and integration (providing more easily visualizable predictive information to support human problem solving), without inviting some of the most obvious costs associated with automation of response (complacency and skill degradation). Nevertheless, predicted effects, discussed above, remain uncertain and should be the focus of continued evaluation.
Four-Dimensional Contracts
Air traffic management seeks to solve a four-dimensional space-time problem. Aircraft flight paths in three dimensions of space (latitude, longitude, altitude) must be coordinated over time so as to be conflict free. Currently, controllers and flow managers solve this four-dimensional problem by forming a mental picture of aircraft trajectories in the future. The picture of the future traffic pattern is updated periodically as new data about aircraft positions and weather are obtained. Moreover, current procedures dictate that controllers have control over the aircraft's flight path, so that they can anticipate potential conflicts and plan for the future. The controller also has available display tools for short-term projection of flight paths. Thus, the controller's cognitive skills in planning and the spatiotemporal projection of flight paths, combined with display aids, form the basis for the current system of air traffic management.
Although experienced controllers have developed considerable cognitive skill in trajectory prediction, additional tools may be necessary to facilitate this skill under high workload and as traffic density increases. Such tools have also been proposed because current air traffic management is thought to be less than optimal. There is a disparity between the accurate, fuel-efficient trajectory that an aircraft fitted with a flight management system (FMS) can fly and the more limited, constrained flight path that air traffic management can offer. As a result, the benefits offered by the FMS cannot be realized.
One solution to this problem is to down-link FMS-derived information on the current and future aircraft trajectory to ground air traffic management systems. Automated tools could then be developed to help the controller in using this information to negotiate with the pilot a flight trajectory more compatible with the FMS-derived path and to detect and resolve conflicts over longer periods of time. In particular, automated tools have been proposed to improve capacity through more accurate navigation in four dimensions. Recent work in Europe has been aimed at developing such four-dimensional tools.
Functionality
The Programme for Harmonised Air Traffic Management Research in Eurocontrol (PHARE) has specified a medium-term future air traffic management scenario that comprises (among other things) a suite of tools for pilots and controllers aimed at facilitating trajectory prediction and conflict detection. The medium-term scenario envisions a process of negotiation between airborne and ground-based systems, whereby an agreed flight path can be flown with minimal ground intervention. The resultant trajectory for a given aircraft could then be represented as a four-dimensional "tube" through space. Each aircraft would be assigned a tube, resulting in a number of tubes representing all the traffic in a given airspace.
The four-dimensional tube can be represented as a three-dimensional "bubble" that moves through space such that its position and size are specified functions of time. The precise cross-sectional dimensions of such a tube would vary dynamically with such factors as traffic density and weather disturbances. The tube may grow or shrink asymmetrically along any of the three possible dimensions of space, but it will always remain aligned with respect to the anticipated route. An aircraft would be required to remain within the tube at all times. In fact, the tube is the basis for a negotiated "contract" between the pilot and the controller; hence the term 4-D contract.
Negotiation of the contract will necessarily involve heavy use of data link to support air-ground communication. In an experimental flight management system concept being evaluated by Eurocontrol, aircraft intentions (a four-dimensional trajectory derived by the system) would be down-linked to air traffic management, who would then up-link their requirements in terms of route or time constraints. A prediction system would then calculate the detailed four-dimensional trajectory in a manner that meets the system's specifications within the air traffic management constraints. This would then be down-linked to air traffic management, who will then have to approve the trajectory tube. In principle, the entire trajectory tube, from origin to destination, would be specified and agreed on as the basis for the contract. To reduce data link overhead, default tube parameters could be used for different flight segments, so that only limited tube reference information would need to be up-linked.
In the 4-D contract scenario, the pilot will be free to modify the flight path within the tube. For example, the pilot may deviate laterally at will so long as the left and right tube boundaries are not breached. In this respect, the 4-D contract concept is similar to the U.S. air traffic management concept of free flight, albeit in a more limited form: the degree of pilot freedom lies somewhere between current practices and "advanced" free flight, in which aircraft have much greater flexibility in setting and changing flight paths.
Human Factors Issues
The 4-D contract concept is relatively new, and validations of the concept and human factors studies (simulations and field trials) are still ongoing. Two demonstration projects have been completed to date: PHARE Demonstration 1 and 2, PD/1 and PD/2. PD/1 examined, among other issues, acceptance by controllers of a sector-based 4-D contract system for en route air traffic management. As mentioned earlier, initial analyses suggest that such a system can reduce subjective tactical workload without any cost in user acceptance.
An important technical and procedural issue in the 4-D contract concept is whether the contract applies locally (e.g., to a sector) or globally (to multiple sectors). The original concept envisages a negotiated contract from origin to destination, gate to gate. This is clearly what the pilot and the airlines would prefer, because it would be consistent with the capabilities that the FMS provides and would facilitate pilot flight planning. Controllers, however, may prefer to negotiate contracts sector by sector, because this would give them greater flexibility in management of the traffic pattern, particularly in response to unexpected events, weather disturbances, etc.
Of course, whether or not 4-D contracts are negotiated within or across sectors, the controller will still be responsible for the separation of aircraft. Also, controllers will be able to cancel a contract in response to unanticipated conditions at any time. When this is done, the aircraft will be under tactical control from the ground, as in current practice. Once the condition has passed, however, a new contract can be negotiated. A significant human factors concern is whether such negotiations can be undertaken efficiently and safely in a time-critical environment. Procedures for unambiguous and uninterruptable trajectory or clearance negotiation must be worked out. Thus, 4-D contracts will change aspects of the controller's job, but will not fundamentally alter responsibility for separation. The question is, will the changes affect the ability of controllers to maintain separation?
Only limited data are available to answer this question. On one hand, limited, routine clearances that are communicated to the pilot under the current system may be eliminated, so that controllers may be able to devote greater time to longer-range conflict prediction and planning. On the other hand, the current system is one in which the controller knows that the aircraft will follow a precise, specified path. This will be replaced by a system in which there will be some uncertainty about the aircraft's future position. The larger the 4-D tube, the greater the uncertainty. It is difficult to predict how controllers will react to such a system. One possibility is that they will attempt to reduce the uncertainty by querying pilots more frequently, which would tend to increase communications workload. Endsley (1996b) reported such an effect in an experimental evaluation of a free-flight scenario. However, it is also possible that controllers will adapt to the system and attempt to calibrate their level of uncertainty in advance by negotiating narrower tubes for anticipated problem areas within a sector and larger tubes elsewhere.
The development of the 4-D contract concept has been accompanied by attention to human factors enhancements, particularly in the controller's tools and operating procedures. One product of the PHARE effort will be a set of integrated controller tools, known as the PHARE advanced tools, that incorporates the following capabilities:
Although experienced controllers have developed considerable cognitive skill in trajectory prediction, additional tools may be necessary to facilitate this skill under high workload and as traffic density increases. Such tools have also been proposed because current air traffic management is thought to be less than optimal. There is a disparity between the accurate, fuel-efficient trajectory that an aircraft fitted with a flight management system (FMS) can fly and the more limited, constrained flight path that air traffic management can offer. As a result, the benefits offered by the FMS cannot be realized.
One solution to this problem is to down-link FMS-derived information on the current and future aircraft trajectory to ground air traffic management systems. Automated tools could then be developed to help the controller in using this information to negotiate with the pilot a flight trajectory more compatible with the FMS-derived path and to detect and resolve conflicts over longer periods of time. In particular, automated tools have been proposed to improve capacity through more accurate navigation in four dimensions. Recent work in Europe has been aimed at developing such four-dimensional tools.
Functionality
The Programme for Harmonised Air Traffic Management Research in Eurocontrol (PHARE) has specified a medium-term future air traffic management scenario that comprises (among other things) a suite of tools for pilots and controllers aimed at facilitating trajectory prediction and conflict detection. The medium-term scenario envisions a process of negotiation between airborne and ground-based systems, whereby an agreed flight path can be flown with minimal ground intervention. The resultant trajectory for a given aircraft could then be represented as a four-dimensional "tube" through space. Each aircraft would be assigned a tube, resulting in a number of tubes representing all the traffic in a given airspace.
The four-dimensional tube can be represented as a three-dimensional "bubble" that moves through space such that its position and size are specified functions of time. The precise cross-sectional dimensions of such a tube would vary dynamically with such factors as traffic density and weather disturbances. The tube may grow or shrink asymmetrically along any of the three possible dimensions of space, but it will always remain aligned with respect to the anticipated route. An aircraft would be required to remain within the tube at all times. In fact, the tube is the basis for a negotiated "contract" between the pilot and the controller; hence the term 4-D contract.
Negotiation of the contract will necessarily involve heavy use of data link to support air-ground communication. In an experimental flight management system concept being evaluated by Eurocontrol, aircraft intentions (a four-dimensional trajectory derived by the system) would be down-linked to air traffic management, who would then up-link their requirements in terms of route or time constraints. A prediction system would then calculate the detailed four-dimensional trajectory in a manner that meets the system's specifications within the air traffic management constraints. This would then be down-linked to air traffic management, who will then have to approve the trajectory tube. In principle, the entire trajectory tube, from origin to destination, would be specified and agreed on as the basis for the contract. To reduce data link overhead, default tube parameters could be used for different flight segments, so that only limited tube reference information would need to be up-linked.
In the 4-D contract scenario, the pilot will be free to modify the flight path within the tube. For example, the pilot may deviate laterally at will so long as the left and right tube boundaries are not breached. In this respect, the 4-D contract concept is similar to the U.S. air traffic management concept of free flight, albeit in a more limited form: the degree of pilot freedom lies somewhere between current practices and "advanced" free flight, in which aircraft have much greater flexibility in setting and changing flight paths.
Human Factors Issues
The 4-D contract concept is relatively new, and validations of the concept and human factors studies (simulations and field trials) are still ongoing. Two demonstration projects have been completed to date: PHARE Demonstration 1 and 2, PD/1 and PD/2. PD/1 examined, among other issues, acceptance by controllers of a sector-based 4-D contract system for en route air traffic management. As mentioned earlier, initial analyses suggest that such a system can reduce subjective tactical workload without any cost in user acceptance.
An important technical and procedural issue in the 4-D contract concept is whether the contract applies locally (e.g., to a sector) or globally (to multiple sectors). The original concept envisages a negotiated contract from origin to destination, gate to gate. This is clearly what the pilot and the airlines would prefer, because it would be consistent with the capabilities that the FMS provides and would facilitate pilot flight planning. Controllers, however, may prefer to negotiate contracts sector by sector, because this would give them greater flexibility in management of the traffic pattern, particularly in response to unexpected events, weather disturbances, etc.
Of course, whether or not 4-D contracts are negotiated within or across sectors, the controller will still be responsible for the separation of aircraft. Also, controllers will be able to cancel a contract in response to unanticipated conditions at any time. When this is done, the aircraft will be under tactical control from the ground, as in current practice. Once the condition has passed, however, a new contract can be negotiated. A significant human factors concern is whether such negotiations can be undertaken efficiently and safely in a time-critical environment. Procedures for unambiguous and uninterruptable trajectory or clearance negotiation must be worked out. Thus, 4-D contracts will change aspects of the controller's job, but will not fundamentally alter responsibility for separation. The question is, will the changes affect the ability of controllers to maintain separation?
Only limited data are available to answer this question. On one hand, limited, routine clearances that are communicated to the pilot under the current system may be eliminated, so that controllers may be able to devote greater time to longer-range conflict prediction and planning. On the other hand, the current system is one in which the controller knows that the aircraft will follow a precise, specified path. This will be replaced by a system in which there will be some uncertainty about the aircraft's future position. The larger the 4-D tube, the greater the uncertainty. It is difficult to predict how controllers will react to such a system. One possibility is that they will attempt to reduce the uncertainty by querying pilots more frequently, which would tend to increase communications workload. Endsley (1996b) reported such an effect in an experimental evaluation of a free-flight scenario. However, it is also possible that controllers will adapt to the system and attempt to calibrate their level of uncertainty in advance by negotiating narrower tubes for anticipated problem areas within a sector and larger tubes elsewhere.
The development of the 4-D contract concept has been accompanied by attention to human factors enhancements, particularly in the controller's tools and operating procedures. One product of the PHARE effort will be a set of integrated controller tools, known as the PHARE advanced tools, that incorporates the following capabilities:
- The trajectory predictor predicts the onward path of aircraft in four dimensions.
- The conflict probe predicts conflicts based on the output of the trajectory predictor.
- The flight path monitor detects deviations from planned flight trajectories.
- The negotiation manager processes communication (air-ground and ground-ground) to facilitate flight path negotiation.
- The problem solver proposes solutions to resolve conflicts (as predicted by the conflict probe) or other problems.
- The arrival manager provides scheduling/sequencing information for arrival traffic within the terminal maneuvering area.
- The departure manager provides departure advisories to optimize flow into the en route sector.
- The cooperative tools manage controller workload by monitoring, predicting, and adapting to future task demands.
- The tactical load smoother creates interface enhancements aimed at improving high-level, multisector flow planning.
Another important human factors issue concerns how controllers will interact with displays of the 4-D contracts. Given the graphical and spatial qualities of the four-dimensional concept, it would seem appropriate to make controller interaction with the display also graphical and spatial rather than alphanumeric. This is consistent with a direct-manipulation approach to human-computer interaction. The PHARE advanced tools incorporate the highly interactive problem solver (discussed in the previous section) that permits the controller to resolve traffic conflicts by interacting directly with graphical depictions of tubes in the sky for a given traffic sample. Dynamic data from underlying databases (with respect, for example, to weather and aircraft performance) are transformed and integrated into the displayed flight navigation tubes. Initial trials with active controllers have suggested that this approach can provide substantial benefits in conflict resolution time (and hence traffic throughput), as well as high levels of user acceptance.
Failure Recovery
When the system has saturated the airspace and a partial failure occurs, the use of 4-D contracting tools, like CTAS and interactive conflict resolution tools, may lead to problems in achieving effective and timely recovery.
Automated Support For Airport Operations:
The Surface Movement Advisor Program
Increased automation has been viewed by the FAA as a means of improving the efficiency of airport operations while maintaining safe taxiway navigation, takeoffs, and landings, especially during low-visibility operations. Delays in air traffic translate to extensive costs for airlines and passengers. In response to projected increases in air traffic, the U.S. aviation industry and the FAA are investing billions of dollars to increase airport capacity. However, capacity increases must be supported with improvements in the ability of the national airspace system to take advantage of capacity. Airport operations are a significant candidate for improvement. To address efficiency concerns, the FAA, in collaboration with NASA, is undertaking large-scale development activities to provide controllers, pilots, airfield managers, and airline operations personnel with cues that enhance situation awareness and with automated support of surface traffic planning.
The surface movement advisor project, a joint activity of the FAA and NASA, is being developed to improve the efficiency with which airport facilities operate. The advisor, which is in the concept development and demonstration phase and is undergoing prototype testing at the Atlanta airport, would integrate information from and share information among FAA controllers and air traffic control supervisors, FAA traffic management coordinators (as well as the ATCSCC central flow control facility), ramp operators, airport managers, airline operators, and pilots.
The surface movement advisor architectural concept, is based on a server that collects the following data: information from the FAA tower (e.g., runway configurations), surveillance data (e.g., radar data), weather, real-time aircraft status updates, gate information, airline schedules, and flight plans. The advisor includes automated analysis, prediction, and planning tools (i.e., performance histograms, prediction algorithms, airport operations procedure aids, and statistical analyzers) and distributes, as appropriate, collected data as well as analyses, predictions, and plans to FAA, airport, and airline personnel. This information will assist cooperating personnel to optimize gate resource utilization; balance taxi departure loads; improve gate scheduling and rescheduling; facilitate airport operations analysis; improve crew scheduling; and reduce voice radio traffic.
Potential long-term upgrades to the surface movement advisor include performance improvements based on actual customer use and feedback; integration of air traffic management technologies such as CTAS; implementation of data warehousing and data mining of on-line airport traffic data (e.g., analysis of cause and effect relationships between data sources such as weather, operations, and schedules); implementation of wireless mobile computing technologies to promote wider surface movement advisor data access; and integration of the advisor with surface traffic development and test facilities.
Human Factors Implementation
The surface movement advisor is being developed according to the "build a little, test a little" development philosophy that includes early involvement of users and human factors professionals and ongoing evaluations using mixed methodologies. Its subsystems and features are developed with the support of a surface development and test facility sponsored jointly by NASA and the FAA. The facility supports prototyping and simulation studies that involve test designs developed by human factors professionals and the participation of air traffic controllers, flight data and clearance delivery personnel, traffic management coordinators, tower cab coordinators, supervisors, ramp controllers, "pseudo-pilots," and airport operators. It provides a real-time, interactive, simulated operational airport environment, and its studies support validation of designs as well as development of site-specific adaptations for the surface movement advisor. The facility is therefore both a research and a development tool. In particular, it holds great promise as a testbed for evaluating the interactive effects of introducing multiple automation features into the extant system over time.
Human Factors Issues
As this report notes repeatedly with respect to conflict avoidance in ground operations, one of the greatest causes of mistrust or misapplied trust results when controllers or pilots fail to develop mental models appropriate to the system and task at hand. An appropriate mental model may be considered prerequisite for situation awareness. Both controllers and pilots, as well as airport managers and airline operations personnel, will be expected to develop mental models and situation awareness pertinent to the efficiency of airport operations (e.g., awareness of schedules, gate availabilities, and clearances).
Mental Models, Situation Awareness, and Loss of Skill
The risks of operator inability to develop and apply a mental model of the system's activity, operator inability to monitor fast-paced machine actions, and associated loss of situation awareness are introduced when system automation (e.g., improved surveillance accuracy coupled with sophisticated airport movement area safety system logic, as well as automated planners and schedulers that advise high-efficiency operations relying upon the automated surveillance and processing technology) permits more complex activities (e.g., the movement of greater numbers of aircraft, including under low visibility conditions).
The loss of situation awareness may be accompanied by degradation of skills, if the operator has not maintained proficiency in tasks that are normally performed by the automation. For the surface movement advisor, such tasks may include monitoring the positions and movements of aircraft on the ground (if the surface movement advisor introduces substantial automation to this task), scheduling clearances, coordinating flight plans, and assessing capacity and use of airport resources.
The combination of loss of situation awareness and skill degradation can result in the operator's inability to respond adequately to the failure of the automation. In the case of the surface movement advisor, these risks are introduced at multiple points in the team structure that includes controllers, pilots, airport managers, and airline operations personnel. On that account, each new automation feature should be evaluated for its impact on situation awareness, all team members should be trained to maintain proficiency in automated tasks whenever they are expected to be able to perform those tasks in response to automation failures, and the capability of team members to manage the complexities permitted by automation should be evaluated.
Teams
Airport area automation holds the potential for changing the roles of controllers vis-à-vis pilots, airport personnel, and airline personnel. The data distribution and analysis capabilities of the surface movement advisor introduce the potential for realigning responsibility and authority for performing and managing airport operations among controllers, airport managers, traffic managers, and airline dispatchers and analysts. Realignment may include new responsibilities, new authority structures, new communication and cooperative work links, and new measures of effectiveness (e.g., increasing emphasis on efficiency).
The impact of the surface movement advisor on individual roles should be considered during advisor analysis, design, and test activities. The teamwork associated with it should also be considered. One promising avenue that can contribute to the design of an effective surface movement advisor is the study of computer-supported cooperative work. Such a study should include attention to workload implications of the work requirements and distribution, as well as of the automation of tasks and functions.
Effects of Combining Systems
As noted earlier (with respect to automated ground control systems and with respect to general principles of system development), it is critically important to consider the human factors implications of both phased and simultaneous implementation of two or more automated functions. The combination of automation features can potentially introduce effects that are not predicted from studies or tests of each feature independently. Airport surface automation includes contemplated introduction of many additions or changes to airport operations support tools and, possibly, associated procedures.
For example, tools currently available only to some personnel selectively provide such information as airline schedules, flight plans, gate information, various weather parameters, and runway configuration; the surface movement advisor may combine these tools, or future versions of them, and redistribute the information to additional personnel. In addition to the issue of developing a consistent human-computer interface across the integrated tools, their combination may introduce possibilities for redefining tasks. The redefinition of tasks and potentially more timely and accurate information may introduce possibilities for new procedures.
The general guidance applies here: each change introduced should be studied within the operational context, taking into account all other changes introduced. Such changes may include, for example, the center TRACON automation system final approach spacing tool and the surface conflict avoidance technologies discussed in the previous chapter. The evolution of changes should be centrally monitored and coordinated by a human factors research and development oversight organization.
Failure Recovery
When the system has saturated the airspace and a partial failure occurs, the use of 4-D contracting tools, like CTAS and interactive conflict resolution tools, may lead to problems in achieving effective and timely recovery.
Automated Support For Airport Operations:
The Surface Movement Advisor Program
Increased automation has been viewed by the FAA as a means of improving the efficiency of airport operations while maintaining safe taxiway navigation, takeoffs, and landings, especially during low-visibility operations. Delays in air traffic translate to extensive costs for airlines and passengers. In response to projected increases in air traffic, the U.S. aviation industry and the FAA are investing billions of dollars to increase airport capacity. However, capacity increases must be supported with improvements in the ability of the national airspace system to take advantage of capacity. Airport operations are a significant candidate for improvement. To address efficiency concerns, the FAA, in collaboration with NASA, is undertaking large-scale development activities to provide controllers, pilots, airfield managers, and airline operations personnel with cues that enhance situation awareness and with automated support of surface traffic planning.
The surface movement advisor project, a joint activity of the FAA and NASA, is being developed to improve the efficiency with which airport facilities operate. The advisor, which is in the concept development and demonstration phase and is undergoing prototype testing at the Atlanta airport, would integrate information from and share information among FAA controllers and air traffic control supervisors, FAA traffic management coordinators (as well as the ATCSCC central flow control facility), ramp operators, airport managers, airline operators, and pilots.
The surface movement advisor architectural concept, is based on a server that collects the following data: information from the FAA tower (e.g., runway configurations), surveillance data (e.g., radar data), weather, real-time aircraft status updates, gate information, airline schedules, and flight plans. The advisor includes automated analysis, prediction, and planning tools (i.e., performance histograms, prediction algorithms, airport operations procedure aids, and statistical analyzers) and distributes, as appropriate, collected data as well as analyses, predictions, and plans to FAA, airport, and airline personnel. This information will assist cooperating personnel to optimize gate resource utilization; balance taxi departure loads; improve gate scheduling and rescheduling; facilitate airport operations analysis; improve crew scheduling; and reduce voice radio traffic.
Potential long-term upgrades to the surface movement advisor include performance improvements based on actual customer use and feedback; integration of air traffic management technologies such as CTAS; implementation of data warehousing and data mining of on-line airport traffic data (e.g., analysis of cause and effect relationships between data sources such as weather, operations, and schedules); implementation of wireless mobile computing technologies to promote wider surface movement advisor data access; and integration of the advisor with surface traffic development and test facilities.
Human Factors Implementation
The surface movement advisor is being developed according to the "build a little, test a little" development philosophy that includes early involvement of users and human factors professionals and ongoing evaluations using mixed methodologies. Its subsystems and features are developed with the support of a surface development and test facility sponsored jointly by NASA and the FAA. The facility supports prototyping and simulation studies that involve test designs developed by human factors professionals and the participation of air traffic controllers, flight data and clearance delivery personnel, traffic management coordinators, tower cab coordinators, supervisors, ramp controllers, "pseudo-pilots," and airport operators. It provides a real-time, interactive, simulated operational airport environment, and its studies support validation of designs as well as development of site-specific adaptations for the surface movement advisor. The facility is therefore both a research and a development tool. In particular, it holds great promise as a testbed for evaluating the interactive effects of introducing multiple automation features into the extant system over time.
Human Factors Issues
As this report notes repeatedly with respect to conflict avoidance in ground operations, one of the greatest causes of mistrust or misapplied trust results when controllers or pilots fail to develop mental models appropriate to the system and task at hand. An appropriate mental model may be considered prerequisite for situation awareness. Both controllers and pilots, as well as airport managers and airline operations personnel, will be expected to develop mental models and situation awareness pertinent to the efficiency of airport operations (e.g., awareness of schedules, gate availabilities, and clearances).
Mental Models, Situation Awareness, and Loss of Skill
The risks of operator inability to develop and apply a mental model of the system's activity, operator inability to monitor fast-paced machine actions, and associated loss of situation awareness are introduced when system automation (e.g., improved surveillance accuracy coupled with sophisticated airport movement area safety system logic, as well as automated planners and schedulers that advise high-efficiency operations relying upon the automated surveillance and processing technology) permits more complex activities (e.g., the movement of greater numbers of aircraft, including under low visibility conditions).
The loss of situation awareness may be accompanied by degradation of skills, if the operator has not maintained proficiency in tasks that are normally performed by the automation. For the surface movement advisor, such tasks may include monitoring the positions and movements of aircraft on the ground (if the surface movement advisor introduces substantial automation to this task), scheduling clearances, coordinating flight plans, and assessing capacity and use of airport resources.
The combination of loss of situation awareness and skill degradation can result in the operator's inability to respond adequately to the failure of the automation. In the case of the surface movement advisor, these risks are introduced at multiple points in the team structure that includes controllers, pilots, airport managers, and airline operations personnel. On that account, each new automation feature should be evaluated for its impact on situation awareness, all team members should be trained to maintain proficiency in automated tasks whenever they are expected to be able to perform those tasks in response to automation failures, and the capability of team members to manage the complexities permitted by automation should be evaluated.
Teams
Airport area automation holds the potential for changing the roles of controllers vis-à-vis pilots, airport personnel, and airline personnel. The data distribution and analysis capabilities of the surface movement advisor introduce the potential for realigning responsibility and authority for performing and managing airport operations among controllers, airport managers, traffic managers, and airline dispatchers and analysts. Realignment may include new responsibilities, new authority structures, new communication and cooperative work links, and new measures of effectiveness (e.g., increasing emphasis on efficiency).
The impact of the surface movement advisor on individual roles should be considered during advisor analysis, design, and test activities. The teamwork associated with it should also be considered. One promising avenue that can contribute to the design of an effective surface movement advisor is the study of computer-supported cooperative work. Such a study should include attention to workload implications of the work requirements and distribution, as well as of the automation of tasks and functions.
Effects of Combining Systems
As noted earlier (with respect to automated ground control systems and with respect to general principles of system development), it is critically important to consider the human factors implications of both phased and simultaneous implementation of two or more automated functions. The combination of automation features can potentially introduce effects that are not predicted from studies or tests of each feature independently. Airport surface automation includes contemplated introduction of many additions or changes to airport operations support tools and, possibly, associated procedures.
For example, tools currently available only to some personnel selectively provide such information as airline schedules, flight plans, gate information, various weather parameters, and runway configuration; the surface movement advisor may combine these tools, or future versions of them, and redistribute the information to additional personnel. In addition to the issue of developing a consistent human-computer interface across the integrated tools, their combination may introduce possibilities for redefining tasks. The redefinition of tasks and potentially more timely and accurate information may introduce possibilities for new procedures.
The general guidance applies here: each change introduced should be studied within the operational context, taking into account all other changes introduced. Such changes may include, for example, the center TRACON automation system final approach spacing tool and the surface conflict avoidance technologies discussed in the previous chapter. The evolution of changes should be centrally monitored and coordinated by a human factors research and development oversight organization.
Support Functions
The operation of the air traffic control system is supported by training and maintenance. In both cases, technology plays an important role in how the services are designed and delivered. In this chapter we review trends in technology and the human factors questions surrounding the implementation of new approaches.
Technology Advances
Advances in computing and networking technology have expanded the options for training design and delivery. In addition to classroom and traditional simulation facilities (which are dynamic interactive mockups), training is now possible through personal computer-based simulations and by exercises that are embedded in operational equipment. Moreover, the future holds promise for the use of virtual environment technology in both standalone and networked applications.
As noted in the panel's Phase I report, the Federal Aviation Administration is currently examining methods for providing simulations on personal computers. These computers will provide a high-fidelity emulation of the radar and keyboard as they appear in the live environment. Some specific advantages offered over traditional training simulators are that they can be started, stopped, and rewound at any point in the simulation; they can use voice recognition technology to simulate pseudo-pilots, thus saving on personnel to play these roles; they have software that can generate user-friendly scenarios in minutes; and the costs of purchase and operation are lower.
Another approach to training that is being actively pursued by the military services is to build training capabilities into operational systems. This approach, known as embedded training, can be used either by interrupting or overlying normal operations, allowing operators to enter the training mode using their own equipment. Embedded training can be used to acquire initial skills or for skill maintenance. According to Strasel et al. (1988), a fully functional embedded training system should:
Technology Advances
Advances in computing and networking technology have expanded the options for training design and delivery. In addition to classroom and traditional simulation facilities (which are dynamic interactive mockups), training is now possible through personal computer-based simulations and by exercises that are embedded in operational equipment. Moreover, the future holds promise for the use of virtual environment technology in both standalone and networked applications.
As noted in the panel's Phase I report, the Federal Aviation Administration is currently examining methods for providing simulations on personal computers. These computers will provide a high-fidelity emulation of the radar and keyboard as they appear in the live environment. Some specific advantages offered over traditional training simulators are that they can be started, stopped, and rewound at any point in the simulation; they can use voice recognition technology to simulate pseudo-pilots, thus saving on personnel to play these roles; they have software that can generate user-friendly scenarios in minutes; and the costs of purchase and operation are lower.
Another approach to training that is being actively pursued by the military services is to build training capabilities into operational systems. This approach, known as embedded training, can be used either by interrupting or overlying normal operations, allowing operators to enter the training mode using their own equipment. Embedded training can be used to acquire initial skills or for skill maintenance. According to Strasel et al. (1988), a fully functional embedded training system should:
- Require operators and maintainers to perform normal tasks in response to simulated inputs,
- Present realistic scenarios including degraded modes of operation,
- Provide an interactive capability whereby the system would assess the action of the operator and respond realistically, and
- Record performance and provide feedback after the session.
In the face of increasing automation of the decision-making functions of the air traffic control system, embedded training appears to be an extremely useful approach to helping controllers maintain their skills in manual separation of aircraft a skill that will be called on when an automated system degrades or otherwise forces the controller to function at a lower level of automation. Such training can be scheduled for periods when regular operations are slow.
A number of concerns associated with embedded training should be mentioned. One is that it may cause additional wear on the operational equipment and, as a result, increase the potential for down time and the need for maintenance support. Another is the concern that embedded training must not interfere with operational capabilities or with safety. Yet another is the question of whether the operational system can support embedded training given the requirements for the reliability, availability, maintenance, and staffing associated with training delivery. Good developmental studies can resolve these issues.
Work is also being conducted on using virtual reality in training. In 1996, Science Applications International Corporation conducted a review of virtual reality technology and assessed its readiness for use in training for the FAA. A virtual environment system consists of a human operator, a human-machine interface, and a computer. The computer and the displays and controls in the interface are designed to immerse the operator in a computer-generated three-dimensional environment. In a fully immersive system, the user would experience the virtual world though sight, sound, and touch (Durlach and Mavor, 1995). At the current level of development, there is not sufficient knowledge and computing power to create high-fidelity virtual environment that is interactive with the user in real time. Systems such as SIMNET, which provide real-time interactive training over a computer network, use tank simulators (which provide realistic force feedback) and low-fidelity images.
As the virtual environment technology continues to develop, it will open new opportunities for knowledge acquisition and skill training. Hughes Aircraft (1995) has introduced the virtual tower and the virtual controller. The virtual tower is a desktop trainer with a 180-degree field of view of the airport. It includes a radar situation display and training for the following positions: local tower controller station, ground controller station, flight data position, supervisor station, and pseudo-pilot station air/ground. This system runs on a pentium or 486-66 with 32-bit multitasking processors.
The virtual controller (Hughes Aircraft, 1995) is based on an extension of video game logic. It is a turnkey system that includes voice communications across all training positions as well as radar data, maps, video overlays, fixes, navigational aids, air routes, airspace sectorization, and weather data. The displays are high-resolution color or monochrome. Scenarios can be built rapidly and, once initiated, exercises can be frozen, reversed, and replayed in every detail. This system can be used as a single terminal facility or as a network.
Human Factors Issues
The major concern in designing a training experience is how well the knowledge and skill acquired in the training environment transfers to job performance in the operational environment. This has led to a continuing and not yet well answered question regarding the degree of required fidelity or realism. Transfer of training research suggests that single theories of transfer will not hold for both cognitive and motor tasks (Schmidt and Young, 1987). Hays and Singer (1989) suggest starting with an analysis to determine the major emphasis of the task to be trainedif the task is cognitively oriented, it is likely that the training system should emphasize functional fidelity, which refers to the accuracy of representation of the system's procedures. If there are strong psychomotor elements, then physical fidelity should be emphasized.
Physical fidelity refers to the accuracy of representation of the physical design and layout of the system. Virtual environment training may be particularly suited to increasing the probability of transfer because of its flexibility and feedback capabilities (Durlach and Mavor, 1995). A more complete discussion of training transfer and the surrounding methodological difficulties can be found in Druckman and Bjork (1994).
The equipment, systems, and facilities that support air traffic control and that must be monitored, controlled, and maintained by airway facilities specialists include: equipment internal to facilities (e.g., flight and radar data processors, displays, and workstation devices); equipment that interfaces with the facilities (e.g., radars and communications equipment); and airport local equipment (e.g., runway lighting, local navigation aids, and instrumentation). Automation has been increasingly applied, at varying levels, to the following maintenance tasks: monitoring of equipment status, configuration, and performance; control (including adjustment and configuration); diagnosis of hardware and software problems for equipment and some subsystems; restoration of equipment and some subsystems experiencing outages; validation that equipment is ready for use in air traffic control; logging of maintenance events and related data; and supporting aircraft accident and other incident investigations.
Automation and computer assistance are applied at different levels in different systems. Automation has been widely applied to maintenance activities through built-in equipment-level diagnostic tests and off-line diagnostic tools. A logging system that prompts the manual entry of maintenance and incident data supports both maintenance and incident/accident investigations. In general, automation and computer assistance are provided to support such functions as information retrieval, alarm reporting, remote control, and data recording. Only rarely is automation used to perform such higher-level cognitive functions as trend analysis, failure anticipation, system-level diagnostics and problem determination, and final certification judgments.
History
Historically, the application of automation to relatively lower-level cognitive tasks has been supported by FAA policy. Federal Aviation Administration Order 6000.30B (1991d) and Order 6000.39 (1991a) establish a long-term policy for national airspace system maintenance by recommending that automation be applied to repetitive maintenance tasks and that the airway facilities specialist be left ''free to accomplish higher level, decision-oriented work" (p. 5).
However, changes in this policy have been spurred by recent programs aimed at modernizing the air traffic control system and introducing automation on a large scale. These modernization programs include the advanced automation system (AAS) and its progeny: the replacement of the en route HOST computer; the display system replacement (DSR), which modernizes en route processors and workstations; the standard terminal automation replacement system (STARS), which modernizes the automated radar terminal system processors and workstations; and the tower control computer complex, which modernizes tower processors and workstations. Each of these systems includes new distributed architectures, networks, and built-in automated features that diagnose system faults and perform on-line reconfigurations to maintain system availability.
Formal certification of national airspace system equipment, systems, and services is an especially critical procedural and legal responsibility of system maintainers. This certification responsibility involves the validation by airway facilities specialists that the equipment, systems, and services are performing within specified tolerancesas well as the legal attestation of certification with accompanying accountability. Equipment, systems, and the services they provide (e.g., radar data) can be accepted for use by air traffic controllers only if they have undergone a process of verification followed by formal, written certification. Certification is performed when the equipment or systems are first accepted for use, when they are restored to use after interruption or maintenance, and periodically as scheduled.
The increased reliability of computer-based systems and the automation support for diagnostics that are often embedded in such systems offer the following possibilities for certification: extension of the acceptable certification intervals; increasing reliance on the results of built-in diagnostics that can support certification while the equipment remains in operation; more performance of remote certification, replacing the need to examine the equipment directly; and more automated maintenance logging and equipment performance recording.
These trends and the application of automation to the certification process must be considered in the light of the current formal procedures for performing certification, defined in FAA Order 6000.15B (1991b) and FAA Order 6000.39 (1991a), which emphasize that the choice of methods used for certification including the use of available automation assistancemust be left to the professional judgment of the certifying technician.
A major challenge in the maintenance context is therefore whether and how to apply automation to such higher-level cognitive tasks as estimating trends and predicting, diagnosing interactions between systems, responding to outages that involve interacting system components, and planning maintenance tasks. Such automation would support the turn in maintenance philosophy away from an emphasis on corrective and regularly scheduled preventive maintenance toward an emphasis on performance-based maintenance that takes advantage of automated trend analyses to identify the most efficient scheduling for maintenance to prevent failures.
Under the assumption that sufficient automation support will be available, maintenance philosophy is also turning away from concentration on on-site diagnosis and repair of elements of equipment (using local maintenance control centers) toward more centralized and consolidated operational control centers that remotely monitor and control equipment and systems across facilities, accompanied by automated localization of problems to line-replaceable units that are replaced and sent to contractors for repair. The focus on "systems within one's jurisdiction" is being replaced by a focus on sharing of information, resources, and responsibilities across jurisdictions (Federal Aviation Administration, 1995b, 1995c).
Human Factors Implementation
The maintenance control center (MCC) is the central workstation suite from which maintenance specialists monitor and control the air traffic control system for a given facility or set of sites. The maintenance control center at an en route center, for example, typically consists of an extensive set of separate indicator panels, control panels, keyboards, video displays, and printers that, taken together, provide the capability to monitor and control: radars and radar processing; the HOST components and peripheral devices; computers that process the radar and flight data for presentation at the controllers' workstations; the controllers' plan view displays; communications equipment; and facility environment systems.
Because modernization has been accomplished through many different programs in the FAA involving many different vendors of equipment and systems, and because the national airspace system is the focus of rapidly advancing technologies, maintenance specialists face a variety of new technologies, provided by different vendors, with varying levels of automation and different human-machine interface designs. In contrast, the procedures and human-machine interface for air traffic controllers have undergone more controlled growth and change. The specialists who monitor and control the supporting equipment are typically provided with new monitoring and control devices that are tacked onto the array of such devices for other equipment in a loosely arranged maintenance control center that lacks integration.
The FAA has specified standardized protocols and data acquisition and processing requirements to guide the integration of new national airspace system components and systems in a manner that continues to support the centralized monitoring and control workstations (Federal Aviation Administration, 1994a). However, these and other recommendations (Federal Aviation Administration, 1991a) address only the lower-level automation tasks mentioned above. They do not address the allocation of higher-level tasks between human and machine, the integration of automation functions across disparate systems, or the integration of the associated human-machine interface.
There appears to be a significant need for the specification of a maintenance control center human-computer interface into which all new designs must fit well, and a corresponding need for an overall maintenance control center automation strategy against which proposed automation designs can be evaluated. These same needs apply to the design of tools that support other airway facilities activities, such as off-line diagnosis of equipment, maintenance logging, and maintenance of software.
The ongoing development of the national airspace system infrastructure management system is an opportunity to address this need. It consolidates the existing 79 maintenance control centers into four centralized operations control centers and modernizes the current national maintenance coordination center into a
national operations coordination center. It will be automatically fed data from the centralized operations control centers and may include automation enhancements that support prediction, response, and planning tasks. The success of this consolidation and integration effort hinges on the degree to which new systems pass relevant data to the centralized operations control centers, the manner in which automation is applied at the centralized operations control centers and the national operations coordination center to support the cognitive tasks of the maintainers, and the successful application of human factors research and design efforts to the development of effective centralized operations control centers and national operations coordination center workstations.
It is therefore encouraging that the FAA Technical Center human factors organization is undertaking research and providing design support for the effort.
Human Factors Issues
The impact of automation when new components or systems are introduced is often experienced more directly by maintainers than by air traffic controllers. The new components or systems occasionally include increased automation of air traffic control functions; often they represent modernization of aging equipment without significant change to the human-machine interface for the air traffic controllers. In either case, the new systems increasingly include automation of such maintenance functions as diagnostics, fault localization, status and performance monitoring, logging, and reconfiguration using backup components when the primary components fail. Although these automation enhancements are likely to prove transparent to the air traffic controllers, they can impose on maintenance specialists the requirements to learn new and often complex functional and human-machine characteristics of the modernized equipment.
Cognitive Task Analysis
The FAA has developed detailed job task analyses for maintenance tasks and has applied these analyses to the development of training plans and programs (Federal Aviation Administration, 1993a). The job task analyses have been accompanied by identification of knowledge, skills, and abilities prerequisite for effective task performance, as well as 14 cognitive and sensory attributes of 4 types of task (entry, receipt, analysis, and communication).
The Real Picture Air Traffic Control
Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil).
Preventing collisions is referred to as separation, which is a term used to prevent aircraft from coming too close to each other by use of lateral, vertical and longitudinal separation minima; many aircraft now have collision avoidance systems installed to act as a backup to ATC observation and instructions. In addition to its primary function, the ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAMs (Notices to Airmen).
In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users (private, military, and commercial). When controllers are responsible for separating some or all aircraft, such airspace is called “controlled airspace” in contrast to “uncontrolled airspace” where aircraft may fly without the use of the air traffic control system. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to follow, or merely flight information (in some countries known as advisories) to assist pilots operating in the airspace. In all cases, however, the pilot in command has final responsibility for the safety of the flight, and may deviate from ATC instructions in an emergency.
Although native language for the region is normally used, English language must be used if requested, as required by the international aviation organization ICAO.
History
The first attempts to provide a semblance of air traffic control were based on simple “rules of the road” (European sponsored International Convention for Air Navigation, 1919).
It is considered that the first introduction of Air traffic control was at London’s Croydon Airport in 1921. Archie League, who controlled aircraft using colored flags at what is today Lambert-St. Louis International Airport, is often considered the first air traffic controller.
The first air traffic regulations were established in the United States by the passage of the Air Commerce Act (1926).
Around 1930, radio equipped control towers were established by some local authorities, and in 1933 instrument flying began.
By 1935 several airlines jointly established the first Airway Traffic Control centers to safeguard their aircraft against midair collisions. In 1936 this preliminary effort was transferred to the Federal Government, and the first-generation Air Traffic Control (ATC) System was born.
In 1935, in the US, airlines using the Chicago, Cleveland, and Newark airports agreed to coordinate the handling of airline traffic between those cities. In December, the first Airway Traffic Control Center opened at Newark, New Jersey. The first-generation Air Traffic Control (ATC) System was born. Additional centers at Chicago and Cleveland followed in 1936.
Airport Control
The primary method of controlling the immediate airport environment is visual observation from the control tower. The tower is a tall, windowed structure located on the airport grounds. Aerodrome or Tower controllers are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally 2 to 5 nautical miles (3.7 to 9.2 km) depending on the airport procedures.
Radar displays are also available to controllers at some airports. Controllers may use a radar system called Secondary Surveillance Radar for airborne traffic approaching and departing. These displays include a map of the area, the position of various aircraft, and data tags that include aircraft identification, speed, heading, and other information described in local procedures.
The areas of responsibility for tower controllers fall into three general operational disciplines; Ground Control, Local or Air Control, and Flight Data or Clearance Delivery — other categories, such as Apron Control or Ground Movement Planner, may exist at extremely busy airports. While each tower’s procedures will vary and while there may be multiple teams in larger towers that control multiple runways, the following provides a general concept of the delegation of responsibilities within the tower environment.
Ground Control
Ground Control (sometimes known as Ground Movement Control abbreviated to GMC or Surface Movement Control abbreviated to SMC) is responsible for the airport “maneuvering” areas, or areas not released to the airlines or other users. This generally includes all taxiways, inactive runways, holding areas, and some transitional aprons or intersections where aircraft arrive having vacated the runway and departure gates. Exact areas and control responsibilities are clearly defined in local documents and agreements at each airport. Any aircraft, vehicle, or person walking or working in these areas is required to have clearance from the ground controller.
This is normally done via VHF radio, but there may be special cases where other processes are used. Most aircraft and airside vehicles have radios. Aircraft or vehicles without radios will communicate with the tower via aviation light signals or will be led by vehicles with radios. People working on the airport surface normally have a communications link through which they can reach or be reached by ground control, commonly either by handheld radio or even cell phone. Ground control is vital to the smooth operation of the airport because this position might constrain the order in which the aircraft will be sequenced to depart, which can affect the safety and efficiency of the airport’s operation.
Some busier airports have Surface Movement Radar (SMR), such as, ASDE-3, AMASS or ASDE-X, designed to display aircraft and vehicles on the ground. These are used by the ground controller as an additional tool to control ground traffic, particularly at night or in poor visibility. There are a wide range of capabilities on these systems as they are being modernized. Older systems will display a map of the airport and the target. Newer systems include the capability to display higher quality mapping, radar target, data blocks, and safety alerts, and to interface with other systems such as digital flight strips.
Local or Air Control
Local or Air Control (most often referred to as the generic “Tower” control, although Tower control can also refer to a combination of the local, ground and clearance delivery positions) is responsible for the active runway surfaces. The Air Traffic Control Tower clears aircraft for take off or landing and ensures the runway is clear for these aircraft. If the tower controller detects any unsafe condition, a landing aircraft may be told to “go-around” and be re-sequenced into the landing pattern by the approach or terminal area controller.
Within the tower, a highly disciplined communications process between tower and ground control is an absolute necessity. Ground control must request and gain approval from tower control to cross any active runway with any aircraft or vehicle. Likewise, tower control must ensure ground control is aware of any operations that impact the taxiways and must work with the approach radar controllers to ensure “holes” or “gaps” in the arrival traffic are created (where necessary) to allow taxiing traffic to cross runways and to allow departing aircraft to take off. Crew Resource Management (CRM) procedures are often used to ensure this communication process is efficient and clear, although this is not as prevalent as CRM for pilots.
Flight Data or Clearance delivery
Clearance delivery is the position that issues route clearances to aircraft before they commence taxiing. These contain details of the route that the aircraft is expected to fly after departure. This position will, if necessary, coordinate with the en-route center and national command center or flow control to obtain releases for aircraft. Often however such releases are given automatically or are controlled by local agreements allowing “free-flow” departures. When weather or extremely high demand for a certain airport or airspace becomes a factor, there may be ground “stops” (or “slot delays”) or re-routes may be necessary to ensure the system does not get overloaded.
The primary responsibility of the clearance delivery position is to ensure that the aircraft have the proper route and slot time. This information is also coordinated with the en-route center and the ground controller in order to ensure the aircraft reaches the runway in time to meet the slot time provided by the command center. At some airports the clearance delivery controller also plans aircraft pushbacks and engine starts and is known as Ground Movement Planner (GMP): this position is particularly important at heavily congested airports to prevent taxiway and apron gridlock.
Approach and terminal control
Many airports have a radar control facility that is associated with the airport. In most countries, this is referred to as Approach or Terminal Control; in the U.S., it is often still referred to as a TRACON (Terminal Radar Approach CONtrol) facility. While every airport varies, terminal controllers usually handle traffic in a 30 to 50 nautical mile (56 to 93 km) radius from the airport. Where there are many busy airports in close proximity, one single terminal control may service all the airports. The actual airspace boundaries and altitudes assigned to a terminal control are based on factors such as traffic flows, neighboring airports and terrain, and vary widely from airport to airport: a large and complex example is the London Terminal Control Centre which controls traffic for five main London airports up to 20,000 feet (6,100 m) and out to 100 nautical miles (190 km).
Terminal controllers are responsible for providing all ATC services within their airspace. Traffic flow is broadly divided into departures, arrivals, and overflights. As aircraft move in and out of the terminal airspace, they are handed off to the next appropriate control facility (a control tower, an en-route control facility, or a bordering terminal or approach control). Terminal control is responsible for ensuring that aircraft are at an appropriate altitude when they are handed off, and that aircraft arrive at a suitable rate for landing.
Not all airports have a radar approach or terminal control available. In this case, the en-route center or a neighboring terminal or approach control may co-ordinate directly with the tower on the airport and vector inbound aircraft to a position from where they can land visually. At some of these airports, the tower may provide a non-radar procedural approach service to arriving aircraft handed over from a radar unit before they are visual to land. Some units also have a dedicated approach unit which can provide the procedural approach service either all the time or for any periods of radar outage for any reason.
En-route, center, or area control
ATC provides services to aircraft in flight between airports as well. Pilots fly under one of two sets of rules for separation: Visual Flight Rules (VFR) or Instrument Flight Rules (IFR). Air traffic controllers have different responsibilities to aircraft operating under the different sets of rules. While IFR flights are under positive control, in the US VFR pilots can request flight following, which provides traffic advisory services on a time permitting basis and may also provide assistance in avoiding areas of weather and flight restrictions.
En-route air traffic controllers issue clearances and instructions for airborne aircraft, and pilots are required to comply with these instructions. En-route controllers also provide air traffic control services to many smaller airports around the country, including clearance off of the ground and clearance for approach to an airport. Controllers adhere to a set of separation standards that define the minimum distance allowed between aircraft. These distances vary depending on the equipment and procedures used in providing ATC services.
General characteristics
En-route air traffic controllers work in facilities called Area Control Centers, each of which is commonly referred to as a “Center”. The United States uses the equivalent term Air Route Traffic Control Center (ARTCC). Each center is responsible for many thousands of square miles of airspace (known as a Flight Information Region) and for the airports within that airspace. Centers control IFR aircraft from the time they depart from an airport or terminal area’s airspace to the time they arrive at another airport or terminal area’s airspace. Centers may also “pick up” VFR aircraft that are already airborne and integrate them into the IFR system. These aircraft must, however, remain VFR until the Center provides a clearance.
Center controllers are responsible for climbing the aircraft to their requested altitude while, at the same time, ensuring that the aircraft is properly separated from all other aircraft in the immediate area. Additionally, the aircraft must be placed in a flow consistent with the aircraft’s route of flight. This effort is complicated by crossing traffic, severe weather, special missions that require large airspace allocations, and traffic density. When the aircraft approaches its destination, the center is responsible for meeting altitude restrictions by specific points, as well as providing many destination airports with a traffic flow, which prohibits all of the arrivals being “bunched together”. These “flow restrictions” often begin in the middle of the route, as controllers will position aircraft landing in the same destination so that when the aircraft are close to their destination they are sequenced.
As an aircraft reaches the boundary of a Center’s control area it is “handed off” or “handed over” to the next Area Control Center. In some cases this “hand-off” process involves a transfer of identification and details between controllers so that air traffic control services can be provided in a seamless manner; in other cases local agreements may allow “silent handovers” such that the receiving center does not require any co-ordination if traffic is presented in an agreed manner. After the hand-off, the aircraft is given a frequency change and begins talking to the next controller. This process continues until the aircraft is handed off to a terminal controller (“approach”).
Radar Coverage
Since centers control a large airspace area, they will typically use long range radar that has the capability, at higher altitudes, to see aircraft within 200 nautical miles (370 km) of the radar antenna. They may also use TRACON radar data to control when it provides a better “picture” of the traffic or when it can fill in a portion of the area not covered by the long range radar.
In the U.S. system, at higher altitudes, over 90% of the U.S. airspace is covered by radar and often by multiple radar systems; however, coverage may be inconsistent at lower altitudes used by unpressurized aircraft due to high terrain or distance from radar facilities. A center may require numerous radar systems to cover the airspace assigned to them, and may also rely on pilot position reports from aircraft flying below the floor of radar coverage.
This results in a large amount of data being available to the controller. To address this, automation systems have been designed that consolidate the radar data for the controller. This consolidation includes eliminating duplicate radar returns, ensuring the best radar for each geographical area is providing the data, and displaying the data in an effective format.
Centers also exercise control over traffic travelling over the world’s ocean areas. These areas are also FIRs. Because there are no radar systems available for oceanic control, oceanic controllers provide ATC services using procedural control. These procedures use aircraft position reports, time, altitude, distance, and speed to ensure separation. Controllers record information on flight progress strips and in specially developed oceanic computer systems as aircraft report positions. This process requires that aircraft be separated by greater distances, which reduces the overall capacity for any given route.
Some Air Navigation Service Providers (e.g Airservices Australia, The Federal Aviation Administration, NAVCANADA, etc.) have implemented Automatic Dependent Surveillance - Broadcast (ADS-B) as part of their surveillance capability. This new technology reverses the radar concept. Instead of radar “finding” a target by interrogating the transponder, the ADS-equipped aircraft sends a position report as determined by the navigation equipment on board the aircraft. Normally, ADS operates in the “contract” mode where the aircraft reports a position, automatically or initiated by the pilot, based on a predetermined time interval.
It is also possible for controllers to request more frequent reports to more quickly establish aircraft position for specific reasons. However, since the cost for each report is charged by the ADS service providers to the company operating the aircraft, more frequent reports are not commonly requested except in emergency situations. ADS is significant because it can be used where it is not possible to locate the infrastructure for a radar system (e.g. over water). Computerized radar displays are now being designed to accept ADS inputs as part of the display. This technology is currently used in portions of the North Atlantic and the Pacific by a variety of States who share responsibility for the control of this airspace.
Flight Traffic Mapping
The mapping of flights in real-time is based on the air traffic control system. In 1991, data on the location of aircraft was made available by the Federal Aviation Administration to the airline industry. The National Business Aviation Association (NBAA), the General Aviation Manufacturers Association, the Aircraft Owners & Pilots Association, the Helicopter Association International, and the National Air Transportation Association petitioned the FAA to make ASDI information available on a “need-to-know” basis. Subsequently, NBAA advocated the broad-scale dissemination of air traffic data. The Aircraft Situational Display to Industry (ASDI) system now conveys up-to-date flight information to the airline industry and the public. Some companies that distribute ASDI information are FlightExplorer, FlightView, and FlyteComm. Each company maintains a website that provides free updated information to the public on flight status. Stand-alone programs are also available for displaying the geographic location of airborne IFR (Instrument Flight Rules) air traffic anywhere in the FAA air traffic system. Positions are reported for both commercial and general aviation traffic. The programs can overlay air traffic with a wide selection of maps such as, geo-political boundaries, air traffic control center boundaries, high altitude jet routes, satellite cloud and radar imagery.
Problems
Traffic
The day-to-day problems faced by the air traffic control system are primarily related to the volume of air traffic demand placed on the system, and weather. Several factors dictate the amount of traffic that can land at an airport in a given amount of time. Each landing aircraft must touch down, slow, and exit the runway before the next crosses the beginning of the runway. This process requires at least one and up to four minutes for each aircraft. Allowing for departures between arrivals, each runway can thus handle about 30 arrivals per hour. A large airport with two arrival runways can handle about 60 arrivals per hour in good weather. Problems begin when airlines schedule more arrivals into an airport than can be physically handled, or when delays elsewhere cause groups of aircraft that would otherwise be separated in time to arrive simultaneously. Aircraft must then be delayed in the air by holding over specified locations until they may be safely sequenced to the runway. Up until the 1990s, holding, which has significant environmental and cost implications, was a routine occurrence at many airports. Advances in computers now allow the sequencing of planes hours in advance. Thus, planes may be delayed before they even take off (by being given a “slot”), or may reduce power in flight and proceed more slowly thus significantly reducing the amount of holding.
Weather
Beyond runway capacity issues, weather is a major factor in traffic capacity. Rain or ice and snow on the runway cause landing aircraft to take longer to slow and exit, thus reducing the safe arrival rate and requiring more space between landing aircraft. Fog also requires a decrease in the landing rate. These, in turn, increase airborne delay for holding aircraft. If more aircraft are scheduled than can be safely and efficiently held in the air, a ground delay program may be established, delaying aircraft on the ground before departure due to conditions at the arrival airport.
In Area Control Centers, a major weather problem is thunderstorms, which present a variety of hazards to aircraft. Aircraft will deviate around storms, reducing the capacity of the en-route system by requiring more space per aircraft, or causing congestion as many aircraft try to move through a single hole in a line of thunderstorms. Occasionally weather considerations cause delays to aircraft prior to their departure as routes are closed by thunderstorms.
Much money has been spent on creating software to streamline this process. However, at some ACCs, air traffic controllers still record data for each flight on strips of paper and personally coordinate their paths. In newer sites, these flight progress strips have been replaced by electronic data presented on computer screens. As new equipment is brought in, more and more sites are upgrading away from paper flight strips.
Call Signs
A prerequisite to safe air traffic separation is the assignment and use of distinctive call signs. These are permanently allocated by ICAO (pronounced “eh-key-oh”) on request usually to scheduled flights and some air forces for military flights. They are written callsigns with 3-letter combination like KLM, AAL, SWA, BAW , DLH followed by the flight number, like AAL872, BAW018. As such they appear on flight plans and ATC radar labels.
There are also the audio or Radio-telephony callsigns used on the radio contact between pilots and Air Traffic Control not always identical with the written ones. For example BAW stands for British Airways but on the radio you will only hear the word Speedbird instead. By default, the callsign for any other flight is the registration number (tail number) of the aircraft, such as “N12345” or “C-GABC”.
The term tail number is because a registration number is usually painted somewhere on the tail of a plane, yet this is not a rule. Registration numbers may appear on the engines, anywhere on the fuselage, and often on the wings.
The short Radio-telephony callsigns for these tail numbers is the first letter followed by the last two, like C-BC spoken as Charlie-Bravo-Charlie for C-GABC or the last 3 letters only like ABC spoken Alpha-Bravo-Charlie for C-GABC or the last 3 numbers like 345 spoken as tree-fower-fife for N12345. In the United States the abbreviation of callsigns is required to be a prefix (such as aircraft type, aircraft manufacturer, or first letter of registration) followed by the last three characters of the callsign. This abbreviation is only allowed after communications has been established in each sector.
The flight number part is decided by the aircraft operator. In this arrangement, an identical call sign might well be used for the same scheduled journey each day it is operated, even if the departure time varies a little across different days of the week. The call sign of the return flight often differs only by the final digit from the outbound flight. Generally, airline flight numbers are even if eastbound, and odd if westbound. In order to reduce the possibility of two callsigns on one frequency at any time sounding too similar, a number of airlines, particularly in Europe, have started using alphanumeric callsigns that are not based on flight numbers. For example DLH23LG, spoken as lufthansa-two-tree-lima-golf. Additionally it is the right of the air traffic controller to change the ‘audio’ callsign for the period the flight is in his sector if there is a risk of confusion, usually choosing the tail number instead.
Before around 1980 IATA and ICAO were using the same 2-letter callsigns. Due to the larger number of new airlines after deregulation ICAO established the 3-letter callsigns as mentioned above. The IATA callsigns are currently used in aerodromes on the announcement tables but never used any longer in Air Traffic Control. For example, AA is the IATA callsign for American Airlines — ATC equivalent AAL. Other examples include LY/ELY for El Al, DL/DAL for Delta Air Lines, LH/DLH for Lufthansa etc.
Technology
Many technologies are used in air traffic control systems. Primary and secondary radar are used to enhance a controller’s “situational awareness” within his assigned airspace — all types of aircraft send back primary echoes of varying sizes to controllers’ screens as radar energy is bounced off their skins, and transponder-equipped aircraft reply to secondary radar interrogations by giving an ID (Mode A), an altitude (Mode C) and/or a unique callsign (Mode S). Certain types of weather may also register on the radar screen.
These inputs, added to data from other radars, are correlated to build the air situation. Some basic processing occurs on the radar tracks, such as calculating ground speed and magnetic headings.
Usually, a Flight Data Processing System manages all the flight plan related data, incorporating - in a low or high degree - the information of the track once the correlation between them (flight plan and track) is established. All this information is distributed to modern operational display systems, making it available to controllers.
The FAA has spent over USD$3 billion on software, but a fully-automated system is still over the horizon. In 2002 the UK brought a new area control centre into service at Swanwick, in Hampshire, relieving a busy suburban centre at West Drayton in Middlesex, north of London Heathrow Airport. Software from Lockheed-Martin predominates at Swanwick. The Swanwick facility, however, was initially been troubled by software and communications problems causing delays and occasional shutdowns.
Some tools are available in different domains to help the controller further:
A number of concerns associated with embedded training should be mentioned. One is that it may cause additional wear on the operational equipment and, as a result, increase the potential for down time and the need for maintenance support. Another is the concern that embedded training must not interfere with operational capabilities or with safety. Yet another is the question of whether the operational system can support embedded training given the requirements for the reliability, availability, maintenance, and staffing associated with training delivery. Good developmental studies can resolve these issues.
Work is also being conducted on using virtual reality in training. In 1996, Science Applications International Corporation conducted a review of virtual reality technology and assessed its readiness for use in training for the FAA. A virtual environment system consists of a human operator, a human-machine interface, and a computer. The computer and the displays and controls in the interface are designed to immerse the operator in a computer-generated three-dimensional environment. In a fully immersive system, the user would experience the virtual world though sight, sound, and touch (Durlach and Mavor, 1995). At the current level of development, there is not sufficient knowledge and computing power to create high-fidelity virtual environment that is interactive with the user in real time. Systems such as SIMNET, which provide real-time interactive training over a computer network, use tank simulators (which provide realistic force feedback) and low-fidelity images.
As the virtual environment technology continues to develop, it will open new opportunities for knowledge acquisition and skill training. Hughes Aircraft (1995) has introduced the virtual tower and the virtual controller. The virtual tower is a desktop trainer with a 180-degree field of view of the airport. It includes a radar situation display and training for the following positions: local tower controller station, ground controller station, flight data position, supervisor station, and pseudo-pilot station air/ground. This system runs on a pentium or 486-66 with 32-bit multitasking processors.
The virtual controller (Hughes Aircraft, 1995) is based on an extension of video game logic. It is a turnkey system that includes voice communications across all training positions as well as radar data, maps, video overlays, fixes, navigational aids, air routes, airspace sectorization, and weather data. The displays are high-resolution color or monochrome. Scenarios can be built rapidly and, once initiated, exercises can be frozen, reversed, and replayed in every detail. This system can be used as a single terminal facility or as a network.
Human Factors Issues
The major concern in designing a training experience is how well the knowledge and skill acquired in the training environment transfers to job performance in the operational environment. This has led to a continuing and not yet well answered question regarding the degree of required fidelity or realism. Transfer of training research suggests that single theories of transfer will not hold for both cognitive and motor tasks (Schmidt and Young, 1987). Hays and Singer (1989) suggest starting with an analysis to determine the major emphasis of the task to be trainedif the task is cognitively oriented, it is likely that the training system should emphasize functional fidelity, which refers to the accuracy of representation of the system's procedures. If there are strong psychomotor elements, then physical fidelity should be emphasized.
Physical fidelity refers to the accuracy of representation of the physical design and layout of the system. Virtual environment training may be particularly suited to increasing the probability of transfer because of its flexibility and feedback capabilities (Durlach and Mavor, 1995). A more complete discussion of training transfer and the surrounding methodological difficulties can be found in Druckman and Bjork (1994).
The equipment, systems, and facilities that support air traffic control and that must be monitored, controlled, and maintained by airway facilities specialists include: equipment internal to facilities (e.g., flight and radar data processors, displays, and workstation devices); equipment that interfaces with the facilities (e.g., radars and communications equipment); and airport local equipment (e.g., runway lighting, local navigation aids, and instrumentation). Automation has been increasingly applied, at varying levels, to the following maintenance tasks: monitoring of equipment status, configuration, and performance; control (including adjustment and configuration); diagnosis of hardware and software problems for equipment and some subsystems; restoration of equipment and some subsystems experiencing outages; validation that equipment is ready for use in air traffic control; logging of maintenance events and related data; and supporting aircraft accident and other incident investigations.
Automation and computer assistance are applied at different levels in different systems. Automation has been widely applied to maintenance activities through built-in equipment-level diagnostic tests and off-line diagnostic tools. A logging system that prompts the manual entry of maintenance and incident data supports both maintenance and incident/accident investigations. In general, automation and computer assistance are provided to support such functions as information retrieval, alarm reporting, remote control, and data recording. Only rarely is automation used to perform such higher-level cognitive functions as trend analysis, failure anticipation, system-level diagnostics and problem determination, and final certification judgments.
History
Historically, the application of automation to relatively lower-level cognitive tasks has been supported by FAA policy. Federal Aviation Administration Order 6000.30B (1991d) and Order 6000.39 (1991a) establish a long-term policy for national airspace system maintenance by recommending that automation be applied to repetitive maintenance tasks and that the airway facilities specialist be left ''free to accomplish higher level, decision-oriented work" (p. 5).
However, changes in this policy have been spurred by recent programs aimed at modernizing the air traffic control system and introducing automation on a large scale. These modernization programs include the advanced automation system (AAS) and its progeny: the replacement of the en route HOST computer; the display system replacement (DSR), which modernizes en route processors and workstations; the standard terminal automation replacement system (STARS), which modernizes the automated radar terminal system processors and workstations; and the tower control computer complex, which modernizes tower processors and workstations. Each of these systems includes new distributed architectures, networks, and built-in automated features that diagnose system faults and perform on-line reconfigurations to maintain system availability.
Formal certification of national airspace system equipment, systems, and services is an especially critical procedural and legal responsibility of system maintainers. This certification responsibility involves the validation by airway facilities specialists that the equipment, systems, and services are performing within specified tolerancesas well as the legal attestation of certification with accompanying accountability. Equipment, systems, and the services they provide (e.g., radar data) can be accepted for use by air traffic controllers only if they have undergone a process of verification followed by formal, written certification. Certification is performed when the equipment or systems are first accepted for use, when they are restored to use after interruption or maintenance, and periodically as scheduled.
The increased reliability of computer-based systems and the automation support for diagnostics that are often embedded in such systems offer the following possibilities for certification: extension of the acceptable certification intervals; increasing reliance on the results of built-in diagnostics that can support certification while the equipment remains in operation; more performance of remote certification, replacing the need to examine the equipment directly; and more automated maintenance logging and equipment performance recording.
These trends and the application of automation to the certification process must be considered in the light of the current formal procedures for performing certification, defined in FAA Order 6000.15B (1991b) and FAA Order 6000.39 (1991a), which emphasize that the choice of methods used for certification including the use of available automation assistancemust be left to the professional judgment of the certifying technician.
A major challenge in the maintenance context is therefore whether and how to apply automation to such higher-level cognitive tasks as estimating trends and predicting, diagnosing interactions between systems, responding to outages that involve interacting system components, and planning maintenance tasks. Such automation would support the turn in maintenance philosophy away from an emphasis on corrective and regularly scheduled preventive maintenance toward an emphasis on performance-based maintenance that takes advantage of automated trend analyses to identify the most efficient scheduling for maintenance to prevent failures.
Under the assumption that sufficient automation support will be available, maintenance philosophy is also turning away from concentration on on-site diagnosis and repair of elements of equipment (using local maintenance control centers) toward more centralized and consolidated operational control centers that remotely monitor and control equipment and systems across facilities, accompanied by automated localization of problems to line-replaceable units that are replaced and sent to contractors for repair. The focus on "systems within one's jurisdiction" is being replaced by a focus on sharing of information, resources, and responsibilities across jurisdictions (Federal Aviation Administration, 1995b, 1995c).
Human Factors Implementation
The maintenance control center (MCC) is the central workstation suite from which maintenance specialists monitor and control the air traffic control system for a given facility or set of sites. The maintenance control center at an en route center, for example, typically consists of an extensive set of separate indicator panels, control panels, keyboards, video displays, and printers that, taken together, provide the capability to monitor and control: radars and radar processing; the HOST components and peripheral devices; computers that process the radar and flight data for presentation at the controllers' workstations; the controllers' plan view displays; communications equipment; and facility environment systems.
Because modernization has been accomplished through many different programs in the FAA involving many different vendors of equipment and systems, and because the national airspace system is the focus of rapidly advancing technologies, maintenance specialists face a variety of new technologies, provided by different vendors, with varying levels of automation and different human-machine interface designs. In contrast, the procedures and human-machine interface for air traffic controllers have undergone more controlled growth and change. The specialists who monitor and control the supporting equipment are typically provided with new monitoring and control devices that are tacked onto the array of such devices for other equipment in a loosely arranged maintenance control center that lacks integration.
The FAA has specified standardized protocols and data acquisition and processing requirements to guide the integration of new national airspace system components and systems in a manner that continues to support the centralized monitoring and control workstations (Federal Aviation Administration, 1994a). However, these and other recommendations (Federal Aviation Administration, 1991a) address only the lower-level automation tasks mentioned above. They do not address the allocation of higher-level tasks between human and machine, the integration of automation functions across disparate systems, or the integration of the associated human-machine interface.
There appears to be a significant need for the specification of a maintenance control center human-computer interface into which all new designs must fit well, and a corresponding need for an overall maintenance control center automation strategy against which proposed automation designs can be evaluated. These same needs apply to the design of tools that support other airway facilities activities, such as off-line diagnosis of equipment, maintenance logging, and maintenance of software.
The ongoing development of the national airspace system infrastructure management system is an opportunity to address this need. It consolidates the existing 79 maintenance control centers into four centralized operations control centers and modernizes the current national maintenance coordination center into a
national operations coordination center. It will be automatically fed data from the centralized operations control centers and may include automation enhancements that support prediction, response, and planning tasks. The success of this consolidation and integration effort hinges on the degree to which new systems pass relevant data to the centralized operations control centers, the manner in which automation is applied at the centralized operations control centers and the national operations coordination center to support the cognitive tasks of the maintainers, and the successful application of human factors research and design efforts to the development of effective centralized operations control centers and national operations coordination center workstations.
It is therefore encouraging that the FAA Technical Center human factors organization is undertaking research and providing design support for the effort.
Human Factors Issues
The impact of automation when new components or systems are introduced is often experienced more directly by maintainers than by air traffic controllers. The new components or systems occasionally include increased automation of air traffic control functions; often they represent modernization of aging equipment without significant change to the human-machine interface for the air traffic controllers. In either case, the new systems increasingly include automation of such maintenance functions as diagnostics, fault localization, status and performance monitoring, logging, and reconfiguration using backup components when the primary components fail. Although these automation enhancements are likely to prove transparent to the air traffic controllers, they can impose on maintenance specialists the requirements to learn new and often complex functional and human-machine characteristics of the modernized equipment.
Cognitive Task Analysis
The FAA has developed detailed job task analyses for maintenance tasks and has applied these analyses to the development of training plans and programs (Federal Aviation Administration, 1993a). The job task analyses have been accompanied by identification of knowledge, skills, and abilities prerequisite for effective task performance, as well as 14 cognitive and sensory attributes of 4 types of task (entry, receipt, analysis, and communication).
The Real Picture Air Traffic Control
Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil).
Preventing collisions is referred to as separation, which is a term used to prevent aircraft from coming too close to each other by use of lateral, vertical and longitudinal separation minima; many aircraft now have collision avoidance systems installed to act as a backup to ATC observation and instructions. In addition to its primary function, the ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAMs (Notices to Airmen).
In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users (private, military, and commercial). When controllers are responsible for separating some or all aircraft, such airspace is called “controlled airspace” in contrast to “uncontrolled airspace” where aircraft may fly without the use of the air traffic control system. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to follow, or merely flight information (in some countries known as advisories) to assist pilots operating in the airspace. In all cases, however, the pilot in command has final responsibility for the safety of the flight, and may deviate from ATC instructions in an emergency.
Although native language for the region is normally used, English language must be used if requested, as required by the international aviation organization ICAO.
History
The first attempts to provide a semblance of air traffic control were based on simple “rules of the road” (European sponsored International Convention for Air Navigation, 1919).
It is considered that the first introduction of Air traffic control was at London’s Croydon Airport in 1921. Archie League, who controlled aircraft using colored flags at what is today Lambert-St. Louis International Airport, is often considered the first air traffic controller.
The first air traffic regulations were established in the United States by the passage of the Air Commerce Act (1926).
Around 1930, radio equipped control towers were established by some local authorities, and in 1933 instrument flying began.
By 1935 several airlines jointly established the first Airway Traffic Control centers to safeguard their aircraft against midair collisions. In 1936 this preliminary effort was transferred to the Federal Government, and the first-generation Air Traffic Control (ATC) System was born.
In 1935, in the US, airlines using the Chicago, Cleveland, and Newark airports agreed to coordinate the handling of airline traffic between those cities. In December, the first Airway Traffic Control Center opened at Newark, New Jersey. The first-generation Air Traffic Control (ATC) System was born. Additional centers at Chicago and Cleveland followed in 1936.
Airport Control
The primary method of controlling the immediate airport environment is visual observation from the control tower. The tower is a tall, windowed structure located on the airport grounds. Aerodrome or Tower controllers are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally 2 to 5 nautical miles (3.7 to 9.2 km) depending on the airport procedures.
Radar displays are also available to controllers at some airports. Controllers may use a radar system called Secondary Surveillance Radar for airborne traffic approaching and departing. These displays include a map of the area, the position of various aircraft, and data tags that include aircraft identification, speed, heading, and other information described in local procedures.
The areas of responsibility for tower controllers fall into three general operational disciplines; Ground Control, Local or Air Control, and Flight Data or Clearance Delivery — other categories, such as Apron Control or Ground Movement Planner, may exist at extremely busy airports. While each tower’s procedures will vary and while there may be multiple teams in larger towers that control multiple runways, the following provides a general concept of the delegation of responsibilities within the tower environment.
Ground Control
Ground Control (sometimes known as Ground Movement Control abbreviated to GMC or Surface Movement Control abbreviated to SMC) is responsible for the airport “maneuvering” areas, or areas not released to the airlines or other users. This generally includes all taxiways, inactive runways, holding areas, and some transitional aprons or intersections where aircraft arrive having vacated the runway and departure gates. Exact areas and control responsibilities are clearly defined in local documents and agreements at each airport. Any aircraft, vehicle, or person walking or working in these areas is required to have clearance from the ground controller.
This is normally done via VHF radio, but there may be special cases where other processes are used. Most aircraft and airside vehicles have radios. Aircraft or vehicles without radios will communicate with the tower via aviation light signals or will be led by vehicles with radios. People working on the airport surface normally have a communications link through which they can reach or be reached by ground control, commonly either by handheld radio or even cell phone. Ground control is vital to the smooth operation of the airport because this position might constrain the order in which the aircraft will be sequenced to depart, which can affect the safety and efficiency of the airport’s operation.
Some busier airports have Surface Movement Radar (SMR), such as, ASDE-3, AMASS or ASDE-X, designed to display aircraft and vehicles on the ground. These are used by the ground controller as an additional tool to control ground traffic, particularly at night or in poor visibility. There are a wide range of capabilities on these systems as they are being modernized. Older systems will display a map of the airport and the target. Newer systems include the capability to display higher quality mapping, radar target, data blocks, and safety alerts, and to interface with other systems such as digital flight strips.
Local or Air Control
Local or Air Control (most often referred to as the generic “Tower” control, although Tower control can also refer to a combination of the local, ground and clearance delivery positions) is responsible for the active runway surfaces. The Air Traffic Control Tower clears aircraft for take off or landing and ensures the runway is clear for these aircraft. If the tower controller detects any unsafe condition, a landing aircraft may be told to “go-around” and be re-sequenced into the landing pattern by the approach or terminal area controller.
Within the tower, a highly disciplined communications process between tower and ground control is an absolute necessity. Ground control must request and gain approval from tower control to cross any active runway with any aircraft or vehicle. Likewise, tower control must ensure ground control is aware of any operations that impact the taxiways and must work with the approach radar controllers to ensure “holes” or “gaps” in the arrival traffic are created (where necessary) to allow taxiing traffic to cross runways and to allow departing aircraft to take off. Crew Resource Management (CRM) procedures are often used to ensure this communication process is efficient and clear, although this is not as prevalent as CRM for pilots.
Flight Data or Clearance delivery
Clearance delivery is the position that issues route clearances to aircraft before they commence taxiing. These contain details of the route that the aircraft is expected to fly after departure. This position will, if necessary, coordinate with the en-route center and national command center or flow control to obtain releases for aircraft. Often however such releases are given automatically or are controlled by local agreements allowing “free-flow” departures. When weather or extremely high demand for a certain airport or airspace becomes a factor, there may be ground “stops” (or “slot delays”) or re-routes may be necessary to ensure the system does not get overloaded.
The primary responsibility of the clearance delivery position is to ensure that the aircraft have the proper route and slot time. This information is also coordinated with the en-route center and the ground controller in order to ensure the aircraft reaches the runway in time to meet the slot time provided by the command center. At some airports the clearance delivery controller also plans aircraft pushbacks and engine starts and is known as Ground Movement Planner (GMP): this position is particularly important at heavily congested airports to prevent taxiway and apron gridlock.
Approach and terminal control
Many airports have a radar control facility that is associated with the airport. In most countries, this is referred to as Approach or Terminal Control; in the U.S., it is often still referred to as a TRACON (Terminal Radar Approach CONtrol) facility. While every airport varies, terminal controllers usually handle traffic in a 30 to 50 nautical mile (56 to 93 km) radius from the airport. Where there are many busy airports in close proximity, one single terminal control may service all the airports. The actual airspace boundaries and altitudes assigned to a terminal control are based on factors such as traffic flows, neighboring airports and terrain, and vary widely from airport to airport: a large and complex example is the London Terminal Control Centre which controls traffic for five main London airports up to 20,000 feet (6,100 m) and out to 100 nautical miles (190 km).
Terminal controllers are responsible for providing all ATC services within their airspace. Traffic flow is broadly divided into departures, arrivals, and overflights. As aircraft move in and out of the terminal airspace, they are handed off to the next appropriate control facility (a control tower, an en-route control facility, or a bordering terminal or approach control). Terminal control is responsible for ensuring that aircraft are at an appropriate altitude when they are handed off, and that aircraft arrive at a suitable rate for landing.
Not all airports have a radar approach or terminal control available. In this case, the en-route center or a neighboring terminal or approach control may co-ordinate directly with the tower on the airport and vector inbound aircraft to a position from where they can land visually. At some of these airports, the tower may provide a non-radar procedural approach service to arriving aircraft handed over from a radar unit before they are visual to land. Some units also have a dedicated approach unit which can provide the procedural approach service either all the time or for any periods of radar outage for any reason.
En-route, center, or area control
ATC provides services to aircraft in flight between airports as well. Pilots fly under one of two sets of rules for separation: Visual Flight Rules (VFR) or Instrument Flight Rules (IFR). Air traffic controllers have different responsibilities to aircraft operating under the different sets of rules. While IFR flights are under positive control, in the US VFR pilots can request flight following, which provides traffic advisory services on a time permitting basis and may also provide assistance in avoiding areas of weather and flight restrictions.
En-route air traffic controllers issue clearances and instructions for airborne aircraft, and pilots are required to comply with these instructions. En-route controllers also provide air traffic control services to many smaller airports around the country, including clearance off of the ground and clearance for approach to an airport. Controllers adhere to a set of separation standards that define the minimum distance allowed between aircraft. These distances vary depending on the equipment and procedures used in providing ATC services.
General characteristics
En-route air traffic controllers work in facilities called Area Control Centers, each of which is commonly referred to as a “Center”. The United States uses the equivalent term Air Route Traffic Control Center (ARTCC). Each center is responsible for many thousands of square miles of airspace (known as a Flight Information Region) and for the airports within that airspace. Centers control IFR aircraft from the time they depart from an airport or terminal area’s airspace to the time they arrive at another airport or terminal area’s airspace. Centers may also “pick up” VFR aircraft that are already airborne and integrate them into the IFR system. These aircraft must, however, remain VFR until the Center provides a clearance.
Center controllers are responsible for climbing the aircraft to their requested altitude while, at the same time, ensuring that the aircraft is properly separated from all other aircraft in the immediate area. Additionally, the aircraft must be placed in a flow consistent with the aircraft’s route of flight. This effort is complicated by crossing traffic, severe weather, special missions that require large airspace allocations, and traffic density. When the aircraft approaches its destination, the center is responsible for meeting altitude restrictions by specific points, as well as providing many destination airports with a traffic flow, which prohibits all of the arrivals being “bunched together”. These “flow restrictions” often begin in the middle of the route, as controllers will position aircraft landing in the same destination so that when the aircraft are close to their destination they are sequenced.
As an aircraft reaches the boundary of a Center’s control area it is “handed off” or “handed over” to the next Area Control Center. In some cases this “hand-off” process involves a transfer of identification and details between controllers so that air traffic control services can be provided in a seamless manner; in other cases local agreements may allow “silent handovers” such that the receiving center does not require any co-ordination if traffic is presented in an agreed manner. After the hand-off, the aircraft is given a frequency change and begins talking to the next controller. This process continues until the aircraft is handed off to a terminal controller (“approach”).
Radar Coverage
Since centers control a large airspace area, they will typically use long range radar that has the capability, at higher altitudes, to see aircraft within 200 nautical miles (370 km) of the radar antenna. They may also use TRACON radar data to control when it provides a better “picture” of the traffic or when it can fill in a portion of the area not covered by the long range radar.
In the U.S. system, at higher altitudes, over 90% of the U.S. airspace is covered by radar and often by multiple radar systems; however, coverage may be inconsistent at lower altitudes used by unpressurized aircraft due to high terrain or distance from radar facilities. A center may require numerous radar systems to cover the airspace assigned to them, and may also rely on pilot position reports from aircraft flying below the floor of radar coverage.
This results in a large amount of data being available to the controller. To address this, automation systems have been designed that consolidate the radar data for the controller. This consolidation includes eliminating duplicate radar returns, ensuring the best radar for each geographical area is providing the data, and displaying the data in an effective format.
Centers also exercise control over traffic travelling over the world’s ocean areas. These areas are also FIRs. Because there are no radar systems available for oceanic control, oceanic controllers provide ATC services using procedural control. These procedures use aircraft position reports, time, altitude, distance, and speed to ensure separation. Controllers record information on flight progress strips and in specially developed oceanic computer systems as aircraft report positions. This process requires that aircraft be separated by greater distances, which reduces the overall capacity for any given route.
Some Air Navigation Service Providers (e.g Airservices Australia, The Federal Aviation Administration, NAVCANADA, etc.) have implemented Automatic Dependent Surveillance - Broadcast (ADS-B) as part of their surveillance capability. This new technology reverses the radar concept. Instead of radar “finding” a target by interrogating the transponder, the ADS-equipped aircraft sends a position report as determined by the navigation equipment on board the aircraft. Normally, ADS operates in the “contract” mode where the aircraft reports a position, automatically or initiated by the pilot, based on a predetermined time interval.
It is also possible for controllers to request more frequent reports to more quickly establish aircraft position for specific reasons. However, since the cost for each report is charged by the ADS service providers to the company operating the aircraft, more frequent reports are not commonly requested except in emergency situations. ADS is significant because it can be used where it is not possible to locate the infrastructure for a radar system (e.g. over water). Computerized radar displays are now being designed to accept ADS inputs as part of the display. This technology is currently used in portions of the North Atlantic and the Pacific by a variety of States who share responsibility for the control of this airspace.
Flight Traffic Mapping
The mapping of flights in real-time is based on the air traffic control system. In 1991, data on the location of aircraft was made available by the Federal Aviation Administration to the airline industry. The National Business Aviation Association (NBAA), the General Aviation Manufacturers Association, the Aircraft Owners & Pilots Association, the Helicopter Association International, and the National Air Transportation Association petitioned the FAA to make ASDI information available on a “need-to-know” basis. Subsequently, NBAA advocated the broad-scale dissemination of air traffic data. The Aircraft Situational Display to Industry (ASDI) system now conveys up-to-date flight information to the airline industry and the public. Some companies that distribute ASDI information are FlightExplorer, FlightView, and FlyteComm. Each company maintains a website that provides free updated information to the public on flight status. Stand-alone programs are also available for displaying the geographic location of airborne IFR (Instrument Flight Rules) air traffic anywhere in the FAA air traffic system. Positions are reported for both commercial and general aviation traffic. The programs can overlay air traffic with a wide selection of maps such as, geo-political boundaries, air traffic control center boundaries, high altitude jet routes, satellite cloud and radar imagery.
Problems
Traffic
The day-to-day problems faced by the air traffic control system are primarily related to the volume of air traffic demand placed on the system, and weather. Several factors dictate the amount of traffic that can land at an airport in a given amount of time. Each landing aircraft must touch down, slow, and exit the runway before the next crosses the beginning of the runway. This process requires at least one and up to four minutes for each aircraft. Allowing for departures between arrivals, each runway can thus handle about 30 arrivals per hour. A large airport with two arrival runways can handle about 60 arrivals per hour in good weather. Problems begin when airlines schedule more arrivals into an airport than can be physically handled, or when delays elsewhere cause groups of aircraft that would otherwise be separated in time to arrive simultaneously. Aircraft must then be delayed in the air by holding over specified locations until they may be safely sequenced to the runway. Up until the 1990s, holding, which has significant environmental and cost implications, was a routine occurrence at many airports. Advances in computers now allow the sequencing of planes hours in advance. Thus, planes may be delayed before they even take off (by being given a “slot”), or may reduce power in flight and proceed more slowly thus significantly reducing the amount of holding.
Weather
Beyond runway capacity issues, weather is a major factor in traffic capacity. Rain or ice and snow on the runway cause landing aircraft to take longer to slow and exit, thus reducing the safe arrival rate and requiring more space between landing aircraft. Fog also requires a decrease in the landing rate. These, in turn, increase airborne delay for holding aircraft. If more aircraft are scheduled than can be safely and efficiently held in the air, a ground delay program may be established, delaying aircraft on the ground before departure due to conditions at the arrival airport.
In Area Control Centers, a major weather problem is thunderstorms, which present a variety of hazards to aircraft. Aircraft will deviate around storms, reducing the capacity of the en-route system by requiring more space per aircraft, or causing congestion as many aircraft try to move through a single hole in a line of thunderstorms. Occasionally weather considerations cause delays to aircraft prior to their departure as routes are closed by thunderstorms.
Much money has been spent on creating software to streamline this process. However, at some ACCs, air traffic controllers still record data for each flight on strips of paper and personally coordinate their paths. In newer sites, these flight progress strips have been replaced by electronic data presented on computer screens. As new equipment is brought in, more and more sites are upgrading away from paper flight strips.
Call Signs
A prerequisite to safe air traffic separation is the assignment and use of distinctive call signs. These are permanently allocated by ICAO (pronounced “eh-key-oh”) on request usually to scheduled flights and some air forces for military flights. They are written callsigns with 3-letter combination like KLM, AAL, SWA, BAW , DLH followed by the flight number, like AAL872, BAW018. As such they appear on flight plans and ATC radar labels.
There are also the audio or Radio-telephony callsigns used on the radio contact between pilots and Air Traffic Control not always identical with the written ones. For example BAW stands for British Airways but on the radio you will only hear the word Speedbird instead. By default, the callsign for any other flight is the registration number (tail number) of the aircraft, such as “N12345” or “C-GABC”.
The term tail number is because a registration number is usually painted somewhere on the tail of a plane, yet this is not a rule. Registration numbers may appear on the engines, anywhere on the fuselage, and often on the wings.
The short Radio-telephony callsigns for these tail numbers is the first letter followed by the last two, like C-BC spoken as Charlie-Bravo-Charlie for C-GABC or the last 3 letters only like ABC spoken Alpha-Bravo-Charlie for C-GABC or the last 3 numbers like 345 spoken as tree-fower-fife for N12345. In the United States the abbreviation of callsigns is required to be a prefix (such as aircraft type, aircraft manufacturer, or first letter of registration) followed by the last three characters of the callsign. This abbreviation is only allowed after communications has been established in each sector.
The flight number part is decided by the aircraft operator. In this arrangement, an identical call sign might well be used for the same scheduled journey each day it is operated, even if the departure time varies a little across different days of the week. The call sign of the return flight often differs only by the final digit from the outbound flight. Generally, airline flight numbers are even if eastbound, and odd if westbound. In order to reduce the possibility of two callsigns on one frequency at any time sounding too similar, a number of airlines, particularly in Europe, have started using alphanumeric callsigns that are not based on flight numbers. For example DLH23LG, spoken as lufthansa-two-tree-lima-golf. Additionally it is the right of the air traffic controller to change the ‘audio’ callsign for the period the flight is in his sector if there is a risk of confusion, usually choosing the tail number instead.
Before around 1980 IATA and ICAO were using the same 2-letter callsigns. Due to the larger number of new airlines after deregulation ICAO established the 3-letter callsigns as mentioned above. The IATA callsigns are currently used in aerodromes on the announcement tables but never used any longer in Air Traffic Control. For example, AA is the IATA callsign for American Airlines — ATC equivalent AAL. Other examples include LY/ELY for El Al, DL/DAL for Delta Air Lines, LH/DLH for Lufthansa etc.
Technology
Many technologies are used in air traffic control systems. Primary and secondary radar are used to enhance a controller’s “situational awareness” within his assigned airspace — all types of aircraft send back primary echoes of varying sizes to controllers’ screens as radar energy is bounced off their skins, and transponder-equipped aircraft reply to secondary radar interrogations by giving an ID (Mode A), an altitude (Mode C) and/or a unique callsign (Mode S). Certain types of weather may also register on the radar screen.
These inputs, added to data from other radars, are correlated to build the air situation. Some basic processing occurs on the radar tracks, such as calculating ground speed and magnetic headings.
Usually, a Flight Data Processing System manages all the flight plan related data, incorporating - in a low or high degree - the information of the track once the correlation between them (flight plan and track) is established. All this information is distributed to modern operational display systems, making it available to controllers.
The FAA has spent over USD$3 billion on software, but a fully-automated system is still over the horizon. In 2002 the UK brought a new area control centre into service at Swanwick, in Hampshire, relieving a busy suburban centre at West Drayton in Middlesex, north of London Heathrow Airport. Software from Lockheed-Martin predominates at Swanwick. The Swanwick facility, however, was initially been troubled by software and communications problems causing delays and occasional shutdowns.
Some tools are available in different domains to help the controller further:
- Flight Data Processing Systems: this is the system (usually one per Center) that processes all the information related to the Flight (the Flight Plan), typically in the time horizon from Gate to gate (airport departure/arrival gates). It uses such processed information to invoke other Flight Plan related tools (such as e.g. MTCD), and distributes such processed information to all the stakeholders (Air Traffic Controllers, collateral Centers, Airports, etc).
- STCA (Short Term CA) that checks possible conflicting trajectories in a time horizon of about 2 or 3 minutes (or even less in approach context - 35 seconds in the French Roissy & Orly approach centres) and alerts the controller prior the loss of separation. The algorithms used may also provide in some systems a possible vectoring solution, that is, the manner in which to turn, descend, or climb the aircraft in order to avoid infringing the minimum safety distance or altitude clearance.
- Minimum Safe Altitude Warning (MSAW): a tool that alerts the controller if an aircraft appears to be flying too low to the ground or will impact terrain based on its current altitude and heading.
- System Coordination (SYSCO) to enable controller to negotiate the release of flights from one sector to another.
- Area Penetration Warning (APW) to inform a controller that a flight will penetrate a restricted area.
- Arrival and Departure Manager to help sequence the takeoff and landing of aircraft.
- The Departure Manager (DMAN): A system aid for the ATC at airports, that calculates a planned departure flow with the goal to maintain an optimal throughput at the runway, reduce queuing at holding point and distribute the information to various stakeholders at the airport (i.e. the airline, ground handling and Air Traffic Control (ATC)).
- The Arrival Manager (AMAN): A system aid for the ATC at airports, that calculates a planned Arrival flow with the goal to maintain an optimal throughput at the runway, reduce arrival queuing and distribute the information to various stakeholders.
- passive Final Approach Spacing Tool (pFAST), a CTAS tool, provides runway assignment and sequence number advisories to terminal controllers to improve the arrival rate at congested airports. pFAST was deployed and operational at five US TRACONs before being cancelled. NASA research included an Active FAST capability that also provided vector and speed advisories to implement the runway and sequence advisories.
- Converging Runway Display Aid (CRDA) enables Approach controllers to run two final approaches that intersect and make sure that go arounds are minimized
- Center TRACON Automation System (CTAS) is a suite of human centered decision support tools developed by NASA Ames Research Center. Several of the CTAS tools have been field tested and transitioned to the FAA for operational evaluation and use. Some of the CTAS tools are: Traffic Management Advisor (TMA), passive Final Approach Spacing Tool (pFAST), Collaborative Arrival Planning (CAP), Direct-To (D2), En Route Descent Advisor (EDA) and Multi Center TMA.
- Traffic Management Advisor (TMA), a CTAS tool, is an en route decision support tool that automates time based metering solutions to provide an upper limit of aircraft to a TRACON from the Center over a set period of time. Schedules are determined that will not exceed the specified arrival rate and controllers use the scheduled times to provide the appropriate delay to arrivals while in the en route domain. This results in an overall reduction in en route delays and also moves the delays to more efficient airspace (higher altitudes) than occur if holding near the TRACON boundary is required to not overload the TRACON controllers. TMA is operational at most en route air route traffic control centers (ARTCCs) and continues to be enhanced to address more complex traffic situations (e.g. Adjacent Center Metering (ACM) and En Route Departure Capability (EDC))
- TCD & URET
- In the US, User Request Evaluation Tool (URET) takes paper strips out of the equation for En Route controllers at ARTCCs by providing a display that shows all aircraft that are either in or currently routed into the sector.
- In Europe, several MTCD tools are available: iFACTS (NATS), ERATO (DSNA), VAFORIT (DFS), New FDPS (MASUAC). The SESAR Programme should soon launch new MTCD concepts.
- URET and MTCD provide conflict advisories up to 30 minutes in advance and have a suite of assistance tools that assist in evaluating resolution options and pilot requests.
- Mode S: provides a data downlink of flight parameters via Secondary Surveillance Radars allowing radar processing systems and therefore controllers to see various data on a flight, including airframe unique id (24-bits encoded), indicated airspeed and flight director selected level, amongst others.
- CPDLC: Controller Pilot Data Link Communications — allows digital messages to be sent between controllers and pilots, avoiding the need to use radiotelephony. It is especially useful in areas where difficult-to-use HF radiotelephony was previously used for communication with aircraft, e.g. oceans. This is currently in use in various parts of the world including the Atlantic and Pacific oceans.
- ADS-B: Automatic Dependent Surveillance Broadcast — provides a data downlink of various flight parameters to air traffic control systems via the Transponder (1090 MHz) and reception of those data by other aircraft in the vicinity. The most important is the aircraft’s latitude, longitude and level: such data can be utilized to create a radar-like display of aircraft for controllers and thus allows a form of pseudo-radar control to be done in areas where the installation of radar is either prohibitive on the grounds of low traffic levels, or technically not feasible (e.g. oceans). This is currently in use in Australia and parts of the Pacific Ocean and Alaska.
- The Electronic Flight Strip system (e-strip): A system of electronic flight strips replacing the old paper strips is been used by several Service Providers, such as NAV CANADA, MASUAC, DFS, being produced by several industries, such as Indra Sistemas, Thales Group, Frequentis, Avibit, SAAB etc. E-strips allows controllers to manage electronic flight data online without Paper Strips, reducing the need for manual functions.
Major Accidents
On July 1, 2002 a Tupolev Tu-154 and Boeing 757 collided above Überlingen near the boundary between German and Swiss-controlled airspace when a Skyguide-employed controller (Peter Nielsen), unaware that the flight was receiving instruction from the on-board automatic Traffic Collision Avoidance System software to climb, instructed the southbound Tupolev to descend. See 2002 Überlingen Mid-Air Collision for more on this accident.
The deadliest mid-air crash, the 1996 Charkhi Dadri mid-air collision over India, partly resulted from the fact that the New Delhi-area airspace was shared by departures and arrivals, when in most cases departures and arrivals would use separate airspaces.
The deadliest collision between airliners took place on the ground, on March 27, 1977, in what is known as the Tenerife disaster.
Air navigation service providers (ANSPs) and traffic service providers (ATSPs)
The regulatory function remains the responsibility of the State and can be exercised by Government and/or independent Safety, Airspace and Economic Regulators depending on the national institutional arrangements. Often you will see a division between the Civil Aviation Authority (CAA) (the Regulator) and the ANSP (the Air Navigation Service Provider).
An Air Navigation Service Provider — The air navigation service provider is the authority directly responsible for providing both visual and non-visual aids to navigation within a specific airspace in compliance with, but not limited to, International Civil Aviation Organization (ICAO) Annexes 2, 6, 10 and 11; ICAO Documents 4444 and 9426; and, other international, multi-national, and national policy, agreements or regulations.
An Air Traffic Service Provider is the relevant authority designated by the State responsible for providing air traffic services in the airspace concerned — where airspace is classified as Type A through G airspace. Air traffic service is a generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service).
Both ANSPs and ATSPs can be public, private or corporatized organisations and examples of the different legal models exist throughout the world today. The world’s ANSPs are united in and represented by the Civil Air Navigation Services Organisation (CANSO) based at Amsterdam Airport Schiphol in the Netherlands.
In the United States, the Federal Aviation Administration (FAA) provides this service to all aircraft in the National Airspace System (NAS). With the exception of facilities operated by the Department of Defense (DoD), the FAA is responsible for all aspects of U.S.
Air Traffic Control including hiring and training controllers, although there are contract towers located in many parts of the country. A contract tower is an Airport Traffic Control Tower (ATCT) that performs the same function as an FAA-run ATCT but is staffed by employees of a private company (Martin State Airport in Maryland is an example). DoD facilities are generally staffed by military personnel and operate separately but concurrently with FAA facilities, under similar rules and procedures. In Canada, Air Traffic Control is provided by NAV CANADA, a private, non-share capital corporation that operates Canada’s civil air navigation service.
On July 1, 2002 a Tupolev Tu-154 and Boeing 757 collided above Überlingen near the boundary between German and Swiss-controlled airspace when a Skyguide-employed controller (Peter Nielsen), unaware that the flight was receiving instruction from the on-board automatic Traffic Collision Avoidance System software to climb, instructed the southbound Tupolev to descend. See 2002 Überlingen Mid-Air Collision for more on this accident.
The deadliest mid-air crash, the 1996 Charkhi Dadri mid-air collision over India, partly resulted from the fact that the New Delhi-area airspace was shared by departures and arrivals, when in most cases departures and arrivals would use separate airspaces.
The deadliest collision between airliners took place on the ground, on March 27, 1977, in what is known as the Tenerife disaster.
Air navigation service providers (ANSPs) and traffic service providers (ATSPs)
The regulatory function remains the responsibility of the State and can be exercised by Government and/or independent Safety, Airspace and Economic Regulators depending on the national institutional arrangements. Often you will see a division between the Civil Aviation Authority (CAA) (the Regulator) and the ANSP (the Air Navigation Service Provider).
An Air Navigation Service Provider — The air navigation service provider is the authority directly responsible for providing both visual and non-visual aids to navigation within a specific airspace in compliance with, but not limited to, International Civil Aviation Organization (ICAO) Annexes 2, 6, 10 and 11; ICAO Documents 4444 and 9426; and, other international, multi-national, and national policy, agreements or regulations.
An Air Traffic Service Provider is the relevant authority designated by the State responsible for providing air traffic services in the airspace concerned — where airspace is classified as Type A through G airspace. Air traffic service is a generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service).
Both ANSPs and ATSPs can be public, private or corporatized organisations and examples of the different legal models exist throughout the world today. The world’s ANSPs are united in and represented by the Civil Air Navigation Services Organisation (CANSO) based at Amsterdam Airport Schiphol in the Netherlands.
In the United States, the Federal Aviation Administration (FAA) provides this service to all aircraft in the National Airspace System (NAS). With the exception of facilities operated by the Department of Defense (DoD), the FAA is responsible for all aspects of U.S.
Air Traffic Control including hiring and training controllers, although there are contract towers located in many parts of the country. A contract tower is an Airport Traffic Control Tower (ATCT) that performs the same function as an FAA-run ATCT but is staffed by employees of a private company (Martin State Airport in Maryland is an example). DoD facilities are generally staffed by military personnel and operate separately but concurrently with FAA facilities, under similar rules and procedures. In Canada, Air Traffic Control is provided by NAV CANADA, a private, non-share capital corporation that operates Canada’s civil air navigation service.
- Albania - Agjencia Nacionale e Trafikut Ajror
- Austria - Austro Control
- Australia - Airservices Australia (State Owned Corporation) and the Royal Australian Air Force.
- Belgium - Belgocontrol
- Brazil - Department of Air Space Control (Military Authority) and the National Agency of Civil Aviation
- Bulgaria - Air Traffic Services Authority
- Canada - NAV CANADA - formerly provided by Transport Canada
- Central America - Corporación Centroamericana de Servicios de Navegación Aerea
o Guatemala - DGAC (Dirección General de Aeronáutica Civil)
o El Salvador
o Honduras
o Nicaragua
o Costa Rica - Dirección General de Aviacion Civil
o Belize
o El Salvador
o Honduras
o Nicaragua
o Costa Rica - Dirección General de Aviacion Civil
o Belize
- Colombia - (UAEAC)Aeronáutica Civil Colombiana
- Croatia - Hrvatska kontrola zraène plovidbe (Croatia Control Ltd.)
- Cuba - IACC (Instituto de Aeronáutica Civil de Cuba)
- Czech Republic - Øízení letového provozu ÈR
- Denmark - Naviair (Danish ATC)
- Dominican Republic - DGAC (Dirección General de Aeronáutica Civil)
- Estonia - Estonian Air Navigation Services
- Europe - Eurocontrol - (European Organisation for the Safety of Air Navigation)
- Finland - Finavia
- France - Direction Générale de l’Aviation Civile (DGAC) : Direction des Systèmes de la Navigation Aérienne (DSNA) (Government body)
- Georgia - SAKAERONAVIGATSIA, Ltd. (Georgian Air Navigation)
- Germany - Deutsche Flugsicherung (German ATC)
- Greece - Hellenic Civil Aviation Authority (Hellenic ATC)
- Hong Kong - CAD (Civil Aviation Department)
- Hungary - HungaroControl Magyar Légiforgalmi Szolgálat Zrt. (HungaroControl Hungarian Air Navigation Services Pte. Ltd. Co.)
- Iceland - ISAVIA
- Indonesia - Angkasa Pura II
- Ireland - IAA (Irish Aviation Authority)
- India - Airports Authority of India (AAI) (under Ministry of Civil Aviation, Government Of India)
- Italy - ENAV (Italian ATC)(Ente Nazionale Assistenza al Volo - Italian ATC)
- Jamaica - JCAA (Jamaica Civil Aviation Authority)
- Latvia - LGS (Latvian ATC)
- Lithuania - ANS (Lithuanian ATC)
- Macedonia - DGCA (Macedonian ATC)
- Malaysia - DCA-Department of Civil Aviation
- Mexico - Servicios a la Navegación en el Espacio Aéreo Mexicano
- Netherlands - LVNL (Dutch ATC)
- New Zealand - Airways New Zealand (State Owned Enterprise)
- Norway - Avinor (State-owned private company)
- Pakistan - Civil Aviation Authority (under Government of Pakistan)
- Peru - Centro de Instrucción de Aviación Civil CIAC Civil Aviation Training Center
- Philippines - Air Transportation Office (ATO) (under the Philippine Government)
- Poland - PANSA - Polish Air Navigation Services Agency
- Portugal - NAV - NAV (Portuguese ATC)
- Romania - Romanian Air Traffic Services Administration - (ROMATSA)
- Singapore - CAAS (Civil Aviation Authority of Singapore)
- Serbia - Nacionalna sluzba letenja
- Slovakia - Letové prevádzkové služby Slovenskej republiky
- Slovenia - Slovenia Control
- South Africa - Air Traffic and Navigation Services ,
- Spain - AENA (Spanish ATC and Airports)
- Sweden - The LFV Group (Swedish ATC)
- Switzerland - Skyguide
- Taiwan - ANWS Civil Aeronautical Administration
- Thailand - AEROTHAI (Aeronautical Radio of Thailand)
- Trinidad and Tobago - TTCAA (Trinidad and Tobago Civil Aviation Authority)
- Turkey - DGCA (Turkish Directorate General of Civil Aviation)
- United Kingdom - National Air Traffic Services (49% State Owned Public-Private Partnership)
- United States - Federal Aviation Administration (Government Body)
- Ukraine - Ukrainian State Air Traffic Service Enterprise (UkSATSE)
- Venezuela - INAC (Instituto Nacional de Aviación Civil)
- In the United States, some alterations to traffic control procedures are being examined.
- The Next Generation Air Transportation System examines how to overhaul the United States national airspace system.
- Free flight is a developing air traffic control method that uses no centralized control (e.g. air traffic controllers). Instead, parts of airspace are reserved dynamically and automatically in a distributed way using computer communication to ensure the required separation between aircraft.
In Europe, the SESAR (Single European Sky ATM Research) Programme plans to develop new methods, new technologies, new procedures, new systems to accommodate future (2020 and beyond) Air Traffic Needs.
Many countries have also privatized or corporatized their air navigation service providers.
Air traffic controller
Air traffic controllers are people who operate the air traffic control system to expedite and maintain a safe and orderly flow of air traffic and help prevent mid-air collisions. They apply separation rules to keep each aircraft apart from others in their area of responsibility and move all aircraft safely and efficiently through their assigned sector of airspace. Because controllers have a demonstrably large responsibility while on duty, the ATC profession is often regarded as one of the most difficult jobs today, and can be notoriously stressful.
Although the media frequently refers to them as air controllers, or flight controllers, most air traffic professionals use the term air traffic controller. They are also called air traffic control officers (ATCOs), air traffic control specialists, or simply controllers.
Features of the job
Core Skills of a Controller
Air traffic controllers are generally individuals with excellent memory, are organized, have spatial awareness, are quick with numeric computational skills, are assertive but calm under pressure, and are able to follow and apply rules yet be flexible when necessary. Almost universally, trainee controllers begin work in their twenties, and retire in their fifties. Rigid physical and psychological tests and excellent hearing and speaking skills are a requirement, and controllers must take precautions to remain healthy and avoid certain medications that are banned for controllers.
Most training focuses on honing the ability to absorb data quickly from a variety of sources, and to use this to visualize, in time and space, the position of each aircraft under control, and to project this forward into the near future. This skill is termed situational awareness (having the picture or having the flick), and is central to the job. Maintaining a constantly-moving visual scan among all aircraft under one’s control, without “fixating” on a particular situation, is how controllers help maintain this overall flick. This is then used to make relatively simple rule-based decisions very quickly and accurately to keep aircraft separated in the sky while moving traffic as expeditiously as possible and presenting the traffic in an orderly and useful manner to the next sector.
Communication is a vital part of the job: controllers are trained to precisely focus on the exact words pilots and other controllers speak, because a single misunderstanding about an altitude level or runway number for example can result in tragedy. Controllers communicate with the pilots of aircraft using a push-to-talk radiotelephony system, which has many attendant issues such as the fact only one transmission can be made on a frequency at a time, or transmissions will merge together and be unreadable.
Although local languages are sometimes used in ATC communications, the default language of aviation worldwide is English. Controllers who do not speak this as a first language are generally expected to show a certain minimum level of competency with the language.
Teamwork plays a major role in a controller’s job, not only with other controllers and air traffic staff, but with pilots, engineers and managers. Some controllers feel that this is the only part of their job that is accurately portrayed in the movie Pushing Tin, one of the few movies featuring air traffic controllers.
Area or Enroute
Area controllers are responsible for the safety of aircraft at higher altitudes, in the en route phase of their flight. In most nations they are known as “area” or “enroute” controllers. Airspace under the control of Area controllers is split into sectors which are 3D blocks of airspace of defined dimensions. Each sector will be managed by at least one Area controller. This can be done either with or without the use of radar: radar allows a sector to handle much more traffic, however procedural control is used in many areas where traffic levels do not justify radar or the installation of radar is not feasible.
Area controllers work in Area Control Centers, controlling high-level en-route aircraft, or Terminal Control Centers, controlling aircraft at medium levels climbing and descending from major groups of airports.
Civilian/Military - Public/Private
Most countries’ armed forces employ air traffic controllers, often in most if not all branches of the forces. Although actual terms vary from country to country, controllers are usually enlisted.
In some countries, all air traffic control is done by the military. In other countries, military controllers are only responsible for military airspace and airbases; control of airspace for civilian traffic and civilian airports is done by civilian controllers. Historically in most countries this was part of the government and controllers were civil servants. However, many countries have partly or wholly privatized their air traffic control systems; others are looking to do the same.
Education
Civilian Air Traffic Controllers’ licensing is standardized by international agreement through ICAO. Many countries have Air Traffic Control schools, academies or colleges, often operated by the incumbent provider of air traffic services in that country, but sometimes privately. These train student controllers from walking in off the street to the standards required to hold an Air Traffic Control license, which will contain one or more Ratings. These are sub-qualifications denoting the air traffic control discipline or disciplines in which the person has been trained. ICAO defines five such ratings: Area (procedural), Area Radar, Approach (procedural), Approach Radar and Aerodrome. In the United States, controllers may train in several similar specialties: Tower, Ground-Controlled Approach (GCA), Terminal Radar Control, or Enroute Control (both radar and non-radar). This phase of training takes between 6 months and several years.
Whenever an air traffic controller is posted to a new unit or starts work on a new sector within a particular unit, he or she must undergo a period of training regarding the procedures peculiar to that particular unit and/or sector. The majority of this training is done in a live position controlling real aircraft and is termed On the Job Training (OJT), with a fully-qualified and trained mentor or On the Job Training Instructor (OJTI) also ‘plugged in’ to the sector to give guidance and ready to take over in a second should it become necessary. The length of this phase of training varies from a matter of months to many years, depending on the complexity of the sector.
Only once a person has passed all these training stages, will they be allowed to control on their own.
Work Patterns
Typically, controllers work “in position” for 30 minutes each hour. Except at quieter airports, Air Traffic Control is a 24 hours, 365-days-a-year job. Therefore controllers usually work rotating shifts, including nights, weekends and public holidays. These are usually set twenty eight days in advance. In many countries the structure of controllers’ shift patterns is regulated to allow for adequate time off.
FAA Mandatory Retirement
There is a mandatory retirement age of 56 for controllers who manage air traffic.
The retirement age can be moved up to 61, considering the controller has exceptional experience.
Stress
Many countries regulate the hours that a controller can work on safety grounds. Research has shown that where controllers remain ‘in position’ for more than two hours even at low traffic levels, performance can deteriorate rapidly. Many national regulations therefore feature a two-hour limit on time spent controlling without a break, in addition to controls on length of shifts, number of night shifts done consecutively, length of time off required between shifts, etc. A typical work week for a controller is an 8 hour day, 5 days per week if the facility is correctly staffed. A hiring emergency in the United States has led to some locations having Air Traffic Controllers work 10 hours a day, 6 days a week (mandatory).
Computerization and the Future
Despite years of effort and the billions of dollars that have been spent on computer software designed to assist air traffic control, success has been largely limited to improving the tools at the disposal of the controllers such as computer-enhanced radar. It is likely that in the next few decades, future technology will make the controller more of system manager overseeing decisions made by automated systems and manually intervening to resolve situations not handled well by the computers, rather than being automated out of existence altogether.
However there are problems envisaged with technology that normally takes the controller out of the decision loop but requires the controller to step back in to control exceptional situations: air traffic control is a skill that has to be kept current by regular practice. This in itself may prove to be the largest stumbling block to the introduction of highly automated air traffic control systems.
Career information
Canada
NAV CANADA, the country’s civil air navigation services provider, is a private sector, non-share capital corporation financed through publicly-traded debt. NAV CANADA provides air traffic control, flight information, weather briefings, aeronautical information services, airport advisory services and electronic aids to navigation.
United States
In the U.S., a majority of the air traffic control workforce will retire over the next 10 years. As a result, the Federal Aviation Administration is hiring more than 12,000 new trainees (that take 3-5 years to become fully certified controllers) over the next decade.
There are many avenues to become an Air Traffic Controller. There are 23 CTI (Collegiate Training Initiative) schools around the United States which also provide a college degree in the process. After graduation, personnel are then placed on a list that depicts hiring eligibility.
The Federal Aviation Administration then selects personnel from this list and places new hires in a location. The Federal Aviation Administration also hires ex-controllers from the military. The cut-off age for hire is 31. Finally, the Federal Aviation Administration also hires from the public.
Prior experience or training in air traffic control is not required. However, candidates must have three years of progressively responsible work experience, have completed a full 4-year course of study leading to a bachelor’s degree, or possess an equivalent combination of work experience and college credits. In combining education and experience, 1 year of undergraduate study (30 semester or 45 quarter hours) is equivalent to 9 months of general experience. Certain kinds of aviation experience may be substituted for these requirements.
U.S. citizenship is required. Candidates must be able to speak English clearly enough to be understood over radios, intercoms, and similar communications equipment.
Controllers employed by the Federal Aviation Administration are paid according to the level facility in which they work for, and if they are in training or Certified Professional Controller Status. Controllers make a base salary plus location pay, night pay, Sunday pay, holiday and overtime pay.
A Kansas City Pitch article, “Fear of Flying,” states that the number of air traffic controllers in the United States is decreasing due to low pay and work conditions.
The FAA’s controllers union and FAA management have had considerable differences of opinion, including a breakdown and impasse in contract negotiations followed by an imposed set of working conditions, over the past few years. In 1981, President Ronald Reagan broke a strike of the then air traffic controllers union, PATCO by firing the strikers and permanently banning them from federal service.
United Kingdom
In the UK there are three main routes to becoming an Air Traffic Controller. One is to join NATS as a trainee controller: this is the only way for people wishing to become Area Controllers. Another is to join a non-NATS airport as an Air Traffic Services Assistant with a view to being sponsored by the employer to become an Air Traffic Controller. The third way is to pay for one’s own training to licence level with a view to being hired afterwards (usually by a non-NATS airport).
Controllers can earn up to £85,000 per year depending on employer, experience and the unit at which they are employed (the highest salary potential for NATS Controllers is at Swanwick and Heathrow). Controllers employed by NATS, on appointment as an Air Traffic Controller (3rd anniversary of joining NATS) earn between £40,0000 – £45,000 plus shift pay of approximately £5,250 (Jan ’08).
Popular Accounts
Darcy Frey’s 24 March 1996 New York Times article, “Something’s Got to Give” (which was the inspiration for the movie Pushing Tin, below) presents an image of a busier air traffic control centre being only a few moments of inattention away from a mid-air collision.
Many countries have also privatized or corporatized their air navigation service providers.
Air traffic controller
Air traffic controllers are people who operate the air traffic control system to expedite and maintain a safe and orderly flow of air traffic and help prevent mid-air collisions. They apply separation rules to keep each aircraft apart from others in their area of responsibility and move all aircraft safely and efficiently through their assigned sector of airspace. Because controllers have a demonstrably large responsibility while on duty, the ATC profession is often regarded as one of the most difficult jobs today, and can be notoriously stressful.
Although the media frequently refers to them as air controllers, or flight controllers, most air traffic professionals use the term air traffic controller. They are also called air traffic control officers (ATCOs), air traffic control specialists, or simply controllers.
Features of the job
Core Skills of a Controller
Air traffic controllers are generally individuals with excellent memory, are organized, have spatial awareness, are quick with numeric computational skills, are assertive but calm under pressure, and are able to follow and apply rules yet be flexible when necessary. Almost universally, trainee controllers begin work in their twenties, and retire in their fifties. Rigid physical and psychological tests and excellent hearing and speaking skills are a requirement, and controllers must take precautions to remain healthy and avoid certain medications that are banned for controllers.
Most training focuses on honing the ability to absorb data quickly from a variety of sources, and to use this to visualize, in time and space, the position of each aircraft under control, and to project this forward into the near future. This skill is termed situational awareness (having the picture or having the flick), and is central to the job. Maintaining a constantly-moving visual scan among all aircraft under one’s control, without “fixating” on a particular situation, is how controllers help maintain this overall flick. This is then used to make relatively simple rule-based decisions very quickly and accurately to keep aircraft separated in the sky while moving traffic as expeditiously as possible and presenting the traffic in an orderly and useful manner to the next sector.
Communication is a vital part of the job: controllers are trained to precisely focus on the exact words pilots and other controllers speak, because a single misunderstanding about an altitude level or runway number for example can result in tragedy. Controllers communicate with the pilots of aircraft using a push-to-talk radiotelephony system, which has many attendant issues such as the fact only one transmission can be made on a frequency at a time, or transmissions will merge together and be unreadable.
Although local languages are sometimes used in ATC communications, the default language of aviation worldwide is English. Controllers who do not speak this as a first language are generally expected to show a certain minimum level of competency with the language.
Teamwork plays a major role in a controller’s job, not only with other controllers and air traffic staff, but with pilots, engineers and managers. Some controllers feel that this is the only part of their job that is accurately portrayed in the movie Pushing Tin, one of the few movies featuring air traffic controllers.
Area or Enroute
Area controllers are responsible for the safety of aircraft at higher altitudes, in the en route phase of their flight. In most nations they are known as “area” or “enroute” controllers. Airspace under the control of Area controllers is split into sectors which are 3D blocks of airspace of defined dimensions. Each sector will be managed by at least one Area controller. This can be done either with or without the use of radar: radar allows a sector to handle much more traffic, however procedural control is used in many areas where traffic levels do not justify radar or the installation of radar is not feasible.
Area controllers work in Area Control Centers, controlling high-level en-route aircraft, or Terminal Control Centers, controlling aircraft at medium levels climbing and descending from major groups of airports.
Civilian/Military - Public/Private
Most countries’ armed forces employ air traffic controllers, often in most if not all branches of the forces. Although actual terms vary from country to country, controllers are usually enlisted.
In some countries, all air traffic control is done by the military. In other countries, military controllers are only responsible for military airspace and airbases; control of airspace for civilian traffic and civilian airports is done by civilian controllers. Historically in most countries this was part of the government and controllers were civil servants. However, many countries have partly or wholly privatized their air traffic control systems; others are looking to do the same.
Education
Civilian Air Traffic Controllers’ licensing is standardized by international agreement through ICAO. Many countries have Air Traffic Control schools, academies or colleges, often operated by the incumbent provider of air traffic services in that country, but sometimes privately. These train student controllers from walking in off the street to the standards required to hold an Air Traffic Control license, which will contain one or more Ratings. These are sub-qualifications denoting the air traffic control discipline or disciplines in which the person has been trained. ICAO defines five such ratings: Area (procedural), Area Radar, Approach (procedural), Approach Radar and Aerodrome. In the United States, controllers may train in several similar specialties: Tower, Ground-Controlled Approach (GCA), Terminal Radar Control, or Enroute Control (both radar and non-radar). This phase of training takes between 6 months and several years.
Whenever an air traffic controller is posted to a new unit or starts work on a new sector within a particular unit, he or she must undergo a period of training regarding the procedures peculiar to that particular unit and/or sector. The majority of this training is done in a live position controlling real aircraft and is termed On the Job Training (OJT), with a fully-qualified and trained mentor or On the Job Training Instructor (OJTI) also ‘plugged in’ to the sector to give guidance and ready to take over in a second should it become necessary. The length of this phase of training varies from a matter of months to many years, depending on the complexity of the sector.
Only once a person has passed all these training stages, will they be allowed to control on their own.
Work Patterns
Typically, controllers work “in position” for 30 minutes each hour. Except at quieter airports, Air Traffic Control is a 24 hours, 365-days-a-year job. Therefore controllers usually work rotating shifts, including nights, weekends and public holidays. These are usually set twenty eight days in advance. In many countries the structure of controllers’ shift patterns is regulated to allow for adequate time off.
FAA Mandatory Retirement
There is a mandatory retirement age of 56 for controllers who manage air traffic.
The retirement age can be moved up to 61, considering the controller has exceptional experience.
Stress
Many countries regulate the hours that a controller can work on safety grounds. Research has shown that where controllers remain ‘in position’ for more than two hours even at low traffic levels, performance can deteriorate rapidly. Many national regulations therefore feature a two-hour limit on time spent controlling without a break, in addition to controls on length of shifts, number of night shifts done consecutively, length of time off required between shifts, etc. A typical work week for a controller is an 8 hour day, 5 days per week if the facility is correctly staffed. A hiring emergency in the United States has led to some locations having Air Traffic Controllers work 10 hours a day, 6 days a week (mandatory).
Computerization and the Future
Despite years of effort and the billions of dollars that have been spent on computer software designed to assist air traffic control, success has been largely limited to improving the tools at the disposal of the controllers such as computer-enhanced radar. It is likely that in the next few decades, future technology will make the controller more of system manager overseeing decisions made by automated systems and manually intervening to resolve situations not handled well by the computers, rather than being automated out of existence altogether.
However there are problems envisaged with technology that normally takes the controller out of the decision loop but requires the controller to step back in to control exceptional situations: air traffic control is a skill that has to be kept current by regular practice. This in itself may prove to be the largest stumbling block to the introduction of highly automated air traffic control systems.
Career information
Canada
NAV CANADA, the country’s civil air navigation services provider, is a private sector, non-share capital corporation financed through publicly-traded debt. NAV CANADA provides air traffic control, flight information, weather briefings, aeronautical information services, airport advisory services and electronic aids to navigation.
United States
In the U.S., a majority of the air traffic control workforce will retire over the next 10 years. As a result, the Federal Aviation Administration is hiring more than 12,000 new trainees (that take 3-5 years to become fully certified controllers) over the next decade.
There are many avenues to become an Air Traffic Controller. There are 23 CTI (Collegiate Training Initiative) schools around the United States which also provide a college degree in the process. After graduation, personnel are then placed on a list that depicts hiring eligibility.
The Federal Aviation Administration then selects personnel from this list and places new hires in a location. The Federal Aviation Administration also hires ex-controllers from the military. The cut-off age for hire is 31. Finally, the Federal Aviation Administration also hires from the public.
Prior experience or training in air traffic control is not required. However, candidates must have three years of progressively responsible work experience, have completed a full 4-year course of study leading to a bachelor’s degree, or possess an equivalent combination of work experience and college credits. In combining education and experience, 1 year of undergraduate study (30 semester or 45 quarter hours) is equivalent to 9 months of general experience. Certain kinds of aviation experience may be substituted for these requirements.
U.S. citizenship is required. Candidates must be able to speak English clearly enough to be understood over radios, intercoms, and similar communications equipment.
Controllers employed by the Federal Aviation Administration are paid according to the level facility in which they work for, and if they are in training or Certified Professional Controller Status. Controllers make a base salary plus location pay, night pay, Sunday pay, holiday and overtime pay.
A Kansas City Pitch article, “Fear of Flying,” states that the number of air traffic controllers in the United States is decreasing due to low pay and work conditions.
The FAA’s controllers union and FAA management have had considerable differences of opinion, including a breakdown and impasse in contract negotiations followed by an imposed set of working conditions, over the past few years. In 1981, President Ronald Reagan broke a strike of the then air traffic controllers union, PATCO by firing the strikers and permanently banning them from federal service.
United Kingdom
In the UK there are three main routes to becoming an Air Traffic Controller. One is to join NATS as a trainee controller: this is the only way for people wishing to become Area Controllers. Another is to join a non-NATS airport as an Air Traffic Services Assistant with a view to being sponsored by the employer to become an Air Traffic Controller. The third way is to pay for one’s own training to licence level with a view to being hired afterwards (usually by a non-NATS airport).
Controllers can earn up to £85,000 per year depending on employer, experience and the unit at which they are employed (the highest salary potential for NATS Controllers is at Swanwick and Heathrow). Controllers employed by NATS, on appointment as an Air Traffic Controller (3rd anniversary of joining NATS) earn between £40,0000 – £45,000 plus shift pay of approximately £5,250 (Jan ’08).
Popular Accounts
Darcy Frey’s 24 March 1996 New York Times article, “Something’s Got to Give” (which was the inspiration for the movie Pushing Tin, below) presents an image of a busier air traffic control centre being only a few moments of inattention away from a mid-air collision.
Global Air Traffic Management
Global Air Traffic Management (GATM) is a concept for satellite-based communication, navigation, surveillance and air traffic management. The Federal Aviation Administration and the International Civil Aviation Organization, a special agency of the United Nations, established GATM standards in order to keep air travel safe and effective in increasingly crowded worldwide air space. Efforts are being made worldwide to test and implement new technologies that will allow GATM to efficiently support Air Traffic Control.
Airservices Australia ADS-B initiative is one of the major implementation programs in this field. This initiative will facilitate the certification of this new technology allowing further implementation.
The two core satellite constellations are the Global Positioning System (GPS) of the USA and the Global Navigation Satellite System (GLONASS) of Russia. The third largest constellations would be Europe’s GALILEO when it becomes fully operational. These systems provide independent capabilities and can be used in combination with future core constellations and augmentation systems. Signals from core satellite are received by ground reference stations and any errors in the signals are identified. Each station in the network relays the data to area-wide master stations where correction information for specific geographical areas is computed. The correction message is prepared and uplinked to a geostationary communication satellite (GEO) via a ground uplink station. This message is broadcast to receivers on board aircraft flying within the broadcast coverage area of the System. The system is known in the USA as WAAS (Wide Area Augmentation System), in Europe as EGNOS (European Geostationary Navigation Overlay System), in Japan as MSAS (MTSAT Satellite Based Augmentation System) and in India as GAGAN (GPS Aided Geo Augmented Navigation).
The system employs various techniques to correct equatorial anomalies. The advantage of the system is, it is Global in scope and it has the potential to support all phases of flight providing a seamless global navigation guidance. This could eliminate the need for a variety of ground and airborne systems that were designed to meet specific requirements for certain phases of flight. Standard and Recommended Practices for the air traffic management based on a global navigation satellite system are developed by ICAO (International Civil Aviation Organization). Thus the system has to meet ICAO standards to become operational.
Air Safety
Air safety is a term encompassing the theory, investigation and categorization of flight failures, and the prevention of such failures through regulation, education and training. It can also be applied in the context of campaigns that inform the public as to the safety of air travel.
Institutions
Certification
In most countries, civil aircraft have to be certified by the Civil Aviation Authority (CAA) to be allowed to fly. The major aviation authorities worldwide are the US Federal Aviation Administration (FAA) the European Aviation Safety Agency (EASA) (which provides regulatory advice to the European Union and to a degree supplanted the regulatory bodies of member countries). FAA and EASA are, in particular, primarily responsible for the certification of the airliners from the two major manufacturers, Boeing and Airbus. Aircraft are certified against gudielines set out in the code for each CAA. Those codes are very similar and differ primarily in equipment and environmental standards. Regulations on maintenance, repair and operation provide further direction to the owners of the aircraft so that the aircraft continues to meet design standards.
United States
During the 1920s, the first laws were passed in the USA to regulate civil aviation. Of particular significance was the Air Commerce Act 1926, which required pilots and aircraft to be examined and licensed, for accidents to be properly investigated, and for the establishment of safety rules and navigation aids, under the Aeronautics Branch of the Department of Commerce.
Despite this, in 1926 and 1927 there were a total of 24 fatal commercial airline crashes, a further 16 in 1928, and 51 in 1929 (killing 61 people), which remains the worst year on record at an accident rate of about 1 for every 1,000,000 miles flown. Based on the current numbers flying, this would equate to 7,000 fatal incidents per year.
The fatal incident rate has declined steadily ever since, and, since 1997 the number of fatal air accidents has been no more than 1 for every 2,000,000,000 person-miles flown (e.g., 100 people flying a plane for 1000 miles counts as 100,000 person-miles, making it comparable with methods of transportation with different numbers of passengers, such as one person driving a car for 100,000 miles, which is also 100,000 person-miles), making it one of the safest modes of transportation, as measured by distance traveled.
A disproportionate number of all U.S. aircraft crashes occur in Alaska, largely as a result of severe weather conditions. Between 1990-2006 there were 1441 commuter and air taxi crashes in the U.S. of which 373 (26%) were fatal, resulting in 1063 deaths (142 occupational pilot deaths). Alaska accounted for 513 (36%) of the total U.S. crashes.
Another aspect of safety is protection from attack. The terrorist attacks of 2001 are not counted as accidents. However, even if they were counted as accidents they would have added only about 2 deaths per 2,000,000,000 person-miles. Unfortunately, only 2 months later, American Airlines Flight 587 crashed in Queens, NY, killing 256 people, including 5 on the ground, causing 2001 to show a very high fatality rate. Even so, the rate that year including the attacks (estimated here to be about 4 deaths per 1,000,000,000 person-miles), may be relatively safe compared to some other forms of transport, if measured by distance traveled.
Safety improvements have resulted from improved aircraft design, engineering and maintenance, the evolution of navigation aids, and safety protocols and procedures.
It is often reported that air travel is the safest in terms of deaths per passenger mile. The National Transportation Safety Board (2006) reports 1.3 deaths per hundred million vehicle miles for travel by car, and 1.7 deaths per hundred million vehicle miles for travel by air. These are not passenger miles. If an airplane has 100 passengers, then the passenger miles are 100 times higher, making the risk 100 times lower. The number of deaths per passenger mile on commercial airlines between 1995 and 2000 is about 3 deaths per 10 billion passenger miles.
Navigation Aids and Instrument Flight
One of the first navigation aids to be introduced (in the USA in the late 1920s) was airfield lighting to assist pilots to make landings in poor weather or after dark. The Precision Approach Path Indicator was developed from this in the 1930s, indicating to the pilot the angle of descent to the airfield. This later became adopted internationally through the standards of the International Civil Aviation Organization (ICAO).
In 1929 Jimmy Doolittle developed instrument flight.
With the spread of radio technology, several experimental radio based navigation aids were developed from the late 1920s onwards. These were most successfully used in conjunction with instruments in the cockpit in the form of Instrument landing systems (ILS), first used by a scheduled flight to make a landing in a snowstorm at Pittsburgh in 1938. A form of ILS was adopted by the ICAO for international use in 1949.
Following the development of radar in World War II, it was deployed as a landing aid for civil aviation in the form of Ground-controlled approach (GCA) systems, joined in 1948 by distance measuring equipment (DME), and in the 1950s by airport surveillance radar as an aid to air traffic control. VHF omnidirectional range (VOR) became the predominate means of route navigation during the 1960s superseding the Non-directional beacon (NDB). The ground based VOR stations were often co-located with DME, so that pilots could know both their radials in degrees with respect to north to, and their slant range distance to, that beacon.
All of the ground-based navigation aids are being supplemented by satellite-based aids like Global Positioning System (GPS), which make it possible for aircrews to know their position with great precision anywhere in the world. With the arrival of Wide Area Augmentation System (WAAS), GPS navigation has become accurate enough for vertical (altitude) as well as horizontal use, and is being used increasingly for instrument approaches as well as en-route navigation. However, since the GPS constellation is a single point of failure that can be switched off by the U.S. military in time of crisis, onboard Inertial Navigation System (INS) or ground-based navigation aids are still required for backup.
Air safety topics
Lightning
Boeing studies have shown that airliners are struck by lightning on average of twice per year. While the “flash and bang” is startling to the passengers and crew, aircraft are able to withstand normal lightning strikes.
The dangers of more powerful positive lightning were not understood until the destruction of a glider in 1999.[5] It has since been suggested that positive lightning may have caused the crash of Pan Am Flight 214 in 1963. At that time aircraft were not designed to withstand such strikes, since their existence was unknown at the time standards were set.
The effects of normal lightning on traditional metal-covered aircraft are well understood and serious damage from a lightning strike on an airplane is rare. However, as more and more aircraft, like the upcoming Boeing 787, whose whole exterior is made of non-conducting composite materials take to the skies, additional design effort and testing must be made before certification authorities will permit these aircraft in commercial service.
Ice and Snow
Snowy and icy conditions are frequent contributors to airline accidents. The December 8, 2005 accident where Southwest Airlines Flight 1248 slid off the end of the runway in heavy snow conditions is just one of many examples. Just as on a road, ice and snow buildup can make braking and steering difficult or impossible.
The icing of wings is another problem and measures have been developed to combat it. Even a small amount of ice or coarse frost can greatly decrease the ability of a wing to develop lift. This could prevent an aircraft from taking off. If ice builds up during flight the result can be catastrophic as evidenced by the crash of American Eagle Flight 4184 (an ATR 72 aircraft) near Roselawn, Indiana on October 31, 1994, killing 68, or Air Florida Flight 90.
Airlines and airports ensure that aircraft are properly de-iced before takeoff whenever the weather threatens to create icing conditions. Modern airliners are designed to prevent ice buildup on wings, engines, and tails (empennage) by either routing heated air from jet engines through the leading edges of the wing, tail, and inlets, or on slower aircraft, by use of inflatable rubber “boots” that expand and break off any accumulated ice.
Finally, airline dispatch offices keep watch on weather along the routes of their flights, helping the pilots avoid the worst of inflight icing conditions. Pilots can also be equipped with an ice detector in order to leave icy areas they have flown into.
Engine Failure
Although aircraft are now designed to fly even after the failure of one or more aircraft engines, the failure of the second engine on one side for example is obviously serious. Losing all engine power is even more serious, as illustrated by the 1970 Dominicana DC-9 air disaster, when fuel contamination caused the failure of both engines. To have an emergency landing site is then very important.
In the 1983 Gimli Glider incident, an Air Canada flight suffered fuel exhaustion during cruise flight, forcing the pilot to glide the plane to an emergency deadstick landing. The automatic deployment of the ram air turbine maintained the necessary hydraulic pressure to the flight controls, so that the pilot was able to land with only a minimal amount of damage to the plane, and minor (evacuation) injuries to a few passengers.
The ultimate form of engine failure, physical separation, occurred in 1979 when a complete engine detached from American Airlines Flight 191, causing damage to the aircraft and loss of control.
Metal Fatigue
Metal fatigue has caused failure either of the engine (for example in the January 8, 1989 Kegworth air disaster), or of the aircraft body, for example the De Havilland Comets in 1953 and 1954 and Aloha Airlines Flight 243 in 1988. Now that the subject is better understood, rigorous inspection and nondestructive testing procedures are in place.
Delamination
Composite materials consist of layers of fibers embedded in a resin matrix. In some cases, especially when subjected to cyclic stress, the fibers may tear off the matrix, the layers of the material then separate from each other - a process called delamination, and form a mica-like structure which then falls apart. As the failure develops inside the material, nothing is shown on the surface; instrument methods (often ultrasound-based) have to be used.
Aircraft have developed delamination problems, but most were discovered before they caused a catastrophic failure. Delamination risk is as old as composite material. Even in the 1940s, several Yakovlev Yak-9s experienced delamination of plywood in their construction.
Stalling
Stalling an aircraft (increasing the angle of attack to a point at which the wings fail to produce enough lift) is a danger, but is normally recoverable. Devices have been developed to warn the pilot as stall approaches. These include stall warning horns (now standard on virtually all powered aircraft), stick shakers and voice warnings. Two stall-related airline accidents were British European Airways Flight 548 in 1972, and the United Airlines Flight 553 crash, while on approach to Chicago Midway International Airport, also in 1972.
Fire
Safety regulations control aircraft materials and the requirements for automated fire safety systems. Usually these requirements take the form of required tests. The tests measure flammability and the toxicity of smoke. When the tests fail, they fail on a prototype in an engineering laboratory, rather than in an aircraft.
Fire on board the aircraft, and more especially the toxic smoke generated, have been the cause of incidents. An electrical fire on Air Canada Flight 797 in 1983 caused the deaths of 23 of the 46 passengers, resulting in the introduction of floor level lighting to assist people to evacuate a smoke-filled aircraft. Two years later a fire on the runway caused the loss of 55 lives, 48 from the effects of incapacitating and subsequently lethal toxic gas and smoke, in the 1985 British Airtours Flight 28M. This incident raised serious concerns relating to survivability, something that prior to 1985 had not been studied in such detail. The swift incursion of the fire into the fuselage and the layout of the aircraft impaired passengers’ ability to evacuate, with areas such as the forward galley area becoming a bottle-neck for escaping passengers, with some dying very close to the exits. A large amount of research into evacuation and cabin and seating layouts was carried at Cranfield Institute to try to measure what makes a good evacuation route which led to the seat layout by Overwing exits being changed by mandate and the examination of evacuation requirements relating to the design of galley areas. The use of smoke hoods or misting systems were also examined although both were rejected.
The cargo holds of most airliners are equipped with “fire bottles” (essentially remote-controlled fire extinguishers) to combat a fire that might occur in with the baggage and freight below the passenger cabin. This was due to an accident in 1996. In May of that year ValuJet Airlines Flight 592 crashed into the Florida Everglades a few minutes after takeoff after a fire broke out in the forward cargo hold. All 110 aboard were killed.
The investigation determined that improperly packaged chemical oxygen generators (used for the drop-down oxygen masks in the aircraft cabin) had been loaded into the cargo hold. Oxygen generators produce oxygen through a chemical reaction that also generates hundreds of degrees of heat. When installed for use in the ceiling above the passenger seats they are surrounded by heat-resistant shielding and present no fire hazard. On this flight they had been put loosely into a cardboard box for shipment from a maintenance facility.
It is likely that one or more of the generators ignited, during or immediately after takeoff, producing an oxygen-rich environment. The cardboard box containing the generators would have quickly caught fire from the heat of the ignited generator. The fire spread to an aircraft tire that was also carried in the hold. Ordinarily the fire would have smothered itself, because of the airtight design of that cargo compartment. But the oxygen generators kept feeding oxygen to the fire, defeating the smothering design of the McDonnell Douglas DC-9 cargo hold. The fire rapidly burned through the passenger cabin floor, incapacitating all aboard with smoke and poisonous gases very quickly. The pilots, although having smoke masks and separate oxygen supplies, had no hope of maintaining control as control cables and electrical wiring burned through.
The maintenance facility (SabreTech) was subjected to large fines and ValuJet, due to this accident and other irregularities, was grounded. The airline reemerged as a smaller airline and eventually merged with AirTran Airways, a smaller carrier. Adopting the acquired airline’s name, the airline has since provided safe service. For the airline industry, rules for the shipment of oxygen generators was severely restricted and cargo holds on larger airliners were required to have “fire bottles” installed.
At one time fire fighting foam paths were laid down before an emergency landing, but the practice was considered only marginally effective, and concerns about the depletion of fire fighting capability due to pre-foaming led the United States FAA to withdraw its recommendation in 1987.
Bird Strike
Bird strike is an aviation term for a collision between a bird and an aircraft. It is a common threat to aircraft safety and has caused a number of fatal accidents. In 1988 an Ethiopian Airlines Boeing 737 sucked pigeons into both engines during take-off and then crashed in an attempt to return to the Bahir Dar airport; of the 104 people aboard, 35 died and 21 were injured. In another incident in 1995, a Dassault Falcon 20 crashed at a Paris airport during an emergency landing attempt after sucking lapwings into an engine, which caused an engine failure and a fire in the airplane fuselage; all 10 people on board were killed. A bird strike is suspected as causing the engines to fail on US Airways 1549 that crash landed onto the Hudson River.
Modern jet engines have the capability of surviving an ingestion of a bird. Small fast planes, such as military jet fighters, are at higher risk than big heavy multi-engine ones. This is due to the fact that the fan of a high-bypass turbofan engine, typical on transport aircraft, acts as a centrifugal separator to force ingested materials (birds, ice, etc.) to the outside of the fan’s disc.
As a result, such materials go through the relatively unobstructed bypass duct, rather than through the core of the engine, which contains the smaller and more delicate compressor blades. Military aircraft designed for high-speed flight typically have pure turbojet, or low-bypass turbofan engines, increasing the risk that ingested materials will get into the core of the engine to cause damage.
The highest risk of the bird strike is during the takeoff and landing, in low altitudes, which is in the vicinity of the airports. Some airports use active countermeasures, ranging from a person with a shotgun through recorded sounds of predators to employing falconers. Poisonous grass can be planted that is not palatable to birds, nor to insects that attract insectivorous birds. Passive countermeasures involve sensible land-use management, avoiding conditions attracting flocks of birds to the area (eg. landfills). Another tactic found effective is to let the grass at the airfield grow taller (approximately 12 inches (30 centimetres)) as some species of birds won’t land if they cannot see one another.
Ground Damage
Aircraft are occasionally damaged by ground equipment at the airport. In the act of servicing the aircraft between flights a great deal of ground equipment must operate in close proximity to the fuselage and wings. Occasionally the aircraft gets bumped or worse.
Damage may be in the form of simple scratches in the paint or small dents in the skin. However, because aircraft structures (including the outer skin) play such a critical role in the safe operation of a flight, all damage is inspected, measured and possibly tested to ensure that any damage is within safe tolerances. A dent that may look no worse than common “parking lot damage” to an automobile can be serious enough to ground an airplane until a repair can be made.
An example of the seriousness of this problem was the December 26, 2005 depressurization incident on Alaska Airlines flight 536. During ground services a baggage handler hit the side of the aircraft with a tug towing a train of baggage carts. This damaged the metal skin of the aircraft.
This damage was not reported and the plane departed. Climbing through 26,000 feet (7,925 metres) the damaged section of the skin gave way due to the growing difference in pressure between the inside of the aircraft and the outside air. The cabin depressurized with a bang, frightening all aboard and necessitating a rapid descent back to denser (breathable) air and an emergency landing. Post landing examination of the fuselage revealed a
12 in × 6 in (30 cm × 15 cm) hole between the middle and forward cargo doors on the right side of the airplane.
The three pieces of ground equipment that most frequently damage aircraft are the passenger boarding bridge, catering trucks, and cargo “beltloaders.” However, any other equipment found on an airport ramp can damage an aircraft through careless use, high winds, mechanical failure, and so on.
The generic industry colloquial term for this damage is “ramp rash”, or “hangar rash”.
Volcanic Ash
Plumes of volcanic ash near active volcanoes present a risk especially for night flights. The ash is hard and abrasive and can quickly cause significant wear on the propellers and turbocompressor blades, and scratch the cabin windows, impairing visibility.
It contaminates fuel and water systems, can jam gears, and can cause a flameout of the engines. Its particles have low melting point, so they melt in the combustion chamber and the ceramic mass then sticks on the turbine blades, fuel nozzles, and the combustors, which can lead to a total engine failure. It can get inside the cabin and contaminate everything there, and can damage the airplane electronics.
There are many instances of damage to jet aircraft from ash encounters. In one of them in 1982, British Airways Flight 009 flew through an ash cloud, lost all four engines, and descended from 36,000 ft (11,000 m) to only 12,000 ft (3,700 m) before the flight crew managed to restart the engines.
With the growing density of air traffic, encounters like this are becoming more common. In 1991 the aviation industry decided to set up Volcanic Ash Advisory Centers (VAACs), one for each of 9 regions of the world, acting as liaisons between meteorologists, volcanologists, and the aviation industry.
Human Factors
Human factors including pilot error are another potential danger, and currently the most common factor of aviation crashes. Much progress in applying human factors to improving aviation safety was made around the time of World War II by people such as Paul Fitts and Alphonse Chapanis.
However, there has been progress in safety throughout the history of aviation, such as the development of the pilot’s checklist in 1937. Pilot error and improper communication are often factors in the collision of aircraft. This can take place in the air (1978 Pacific Southwest Airlines Flight 182) (TCAS) or on the ground (1977 Tenerife disaster) (RAAS).
The ability of the flight crew to maintain situational awareness is a critical human factor in air safety. Human factors training is available to general aviation pilots and called single pilot resource management training.
Failure of the pilots to properly monitor the flight instruments resulted in the crash of Eastern Air Lines Flight 40 in 1972 (CFIT), and error during take-off and landing can have catastrophic consequences, for example cause the crash of Prinair Flight 191 on landing, also in 1972.
Rarely, flight crew members are arrested or subject to disciplinary action for being intoxicated on the job. In 1990, three Northwest Airlines crew members were sentenced to jail for flying from Fargo, North Dakota to Minneapolis-Saint Paul International Airport while drunk.
In 2001, Northwest fired a pilot who failed a breathalyzer test after flying from San Antonio, Texas to Minneapolis-Saint Paul. In July 2002, two America West Airlines pilots were arrested just before they were scheduled to fly from Miami, Florida to Phoenix, Arizona because they had been drinking alcohol.
The pilots have been fired from America West and the FAA revoked their pilot’s licenses. As of 2005 they await trial in a Florida court. The incident created a public relations problem and America West has become the object of many jokes about drunk pilots. At least one fatal airliner accident involving drunk pilots has occurred when Aero Flight 311 crashed killing all 25 on board in 1961, which underscores the role that poor human choices can play in air accidents.
Human factors incidents are not limited to errors by the pilots. The failure to close a cargo door properly on Turkish Airlines Flight 981 in 1974 resulted in the loss of the aircraft - however the design of the cargo door latch was also a major factor in the incident.
In the case of Japan Airlines Flight 123, improper maintenance resulted in the loss of the vertical stabilizer.
Controlled flight into terrain
Controlled flight into terrain is a class of accident in which an undamaged aircraft is flown, under control, into terrain. CFIT accidents typically are a result of pilot error or of navigational system error. Some pilots, convinced that advanced electronic navigation systems such as GPS and inertial guidance systems (inertial navigation system or INS) coupled with flight management system computers, or over-reliance on them, are partially responsible for these accidents, have called CFIT accidents “computerized flight into terrain”.
Failure to protect Instrument Landing System critical areas can also cause controlled flight into terrain. Crew awareness and monitoring of navigational systems can prevent or eliminate CFIT accidents. Crew Resource Management is a modern method now widely used to improve the human factors of air safety. The Aviation Safety Reporting System, or ASRS is another.
Other technical aids can be used to help pilots maintain situational awareness. A ground proximity warning system is an on-board system that will alert a pilot if the aircraft is about to fly into the ground. Also, air traffic controllers constantly monitor flights from the ground and at airports.
Terrorism
Terrorism can also be considered a human factor. Crews are normally trained to handle hijack situations. Prior to the September 11, 2001 attacks, hijackings involved hostage negotiations. After the September 11, 2001 attacks, stricter airport security measures are in place to prevent terrorism using a Computer Assisted Passenger Prescreening System, Air Marshals, and precautionary policies. In addition, counter-terrorist organizations monitor potential terrorist activity.
Although most air crews are screened for psychological fitness, some may take suicidal actions. In the case of EgyptAir Flight 990, it appears that the first officer (co-pilot) deliberately dived his aircraft into the Atlantic Ocean while the captain was away from his station, in 1999 off Nantucket, Massachusetts. Motivations are unclear, but recorded inputs from the black boxes showed no mechanical problem, no other aircraft in the area, and was corroborated by the cockpit voice recorder.
The use of certain electronic equipment is partially or entirely prohibited as it may interfere with aircraft operation, such as causing compass deviations.
Use of personal electronic devices and calculators may be prohibited when an aircraft is below 10,000', taking off, or landing. The American Federal Communications Commission (FCC) prohibits the use of a cell phone on most flights, because in-flight usage creates problems with ground-based cells.
There is also concern about possible interference with aircraft navigation systems, although that has never been proven to be a non-serious risk on airliners. A few flights now allow use of cell phones, where the aircraft have been specially wired and certified to meet both FAA and FCC regulations.
Attack by Hostile Country
Aircraft, whether civilian passenger planes or military aircraft, are sometimes attacked in both peacetime and war. One notable example of this is the Sept. 1, 1983 downing by the Soviet Union of Korean Air Lines Flight 007, carrying 269 people (including a sitting U.S. Congressman Larry McDonald).
Airport Design
Airport design and location can have a big impact on air safety, especially since some airports such as Chicago Midway International Airport were originally built for propeller planes and many airports are in congested areas where it is difficult to meet newer safety standards.
For instance, the FAA issued rules in 1999 calling for a runway safety area, usually extending 500 feet (150 m) to each side and 1,000 feet (300 m) beyond the end of a runway. This is intended to cover ninety percent of the cases of an aircraft leaving the runway by providing a buffer space free of obstacles.
Since this is a recent rule, many airports do not meet it. One method of substituting for the 1,000 feet (300 m) at the end of a runway for airports in congested areas is to install an Engineered materials arrestor system, or EMAS. These systems are usually made of a lightweight, crushable concrete that absorbs the energy of the aircraft to bring it to a rapid stop. They have stopped three aircraft (as of 2005) at JFK Airport.
Infection
On an airplane, hundreds of people sit in a confined space for extended periods of time, which increases the risk of transmission of airborne infections.
For this reason, airlines place restrictions on the travel of passengers with known airborne contagious diseases (e.g. tuberculosis). During the severe acute respiratory syndrome (SARS) epidemic of 2003, awareness of the possibility of acquisition of infection on a commercial aircraft reached its zenith when on one flight from Hong Kong to Beijing, 16 of 120 people on the flight developed proven SARS from a single index case.
There is very limited research done on contagious diseases on aircraft. The two most common respiratory pathogens to which air passengers are exposed are parainfluenza and influenza. Certainly, the flight ban imposed following the attacks of September 11, 2001 restricted the ability of influenza to spread around the globe, resulting in a much milder influenza season that year, and the ability of influenza to spread on aircraft has been well documented.
There is no data on the relative contributions of large droplets, small particles, close contact, surface contamination, and certainly no data on the relative importance of any of these methods of transmission for specific diseases, and therefore very little information on how to control the risk of infection. There is no standardisation of air handling by aircraft, installation of HEPA filters or of hand washing by air crew, and no published information on the relative efficacy of any of these interventions in reducing the spread of infection.
Emergency Airplane Evacuations
According to a 2000 report by the National Transportation Safety Board, emergency airplane evacuations happen about once every 11 days in the U.S. While some situations are extremely dire, such as when the plane is on fire, in many cases the greatest challenge for passengers can be the use of the airplane slide.
In a TIME article on the subject, Amanda Ripley reported that when a new supersized Airbus A380 underwent mandatory evacuation tests in 2006, 33 of the 873 evacuating volunteers got hurt. While the evacuation was generally considered a success, one volunteer suffered a broken leg, while the remaining 32 received slide burns. Such accidents are common. In her article, Ripley provides tips on how to make it down the airplane slide without injury.
Runway Safety
Several terms fall under the flight safety topic of of runway safety, including incursion, excursion, and confusion.
Runway excursion is an incident involving only a single aircraft, where it makes an inappropriate exit from the runway. This can happen because of pilot error, poor weather, or a fault with the aircraft. Overrun is a type of excursion where the aircraft is unable to stop before the end of the runway. A recent example of such an event is Air France Flight 358 in 2005. Further examples can be found in the overruns category.
Runway event is another term for a runway accident.
Runway incursion involves a first aircraft, as well as a second aircraft, vehicle, or person. It is defined by the U.S. FAA as: “Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft.”
Runway confusion involves a single aircraft, and is used to describe the error when the aircraft makes “the unintentional use of the wrong runway, or a taxiway, for landing or take-off”. An example of a “Runway confusion” incident can be Comair Flight 5191.
Runway excursion is the most frequent type of landing accident, slightly ahead of runway incursion. For runway accidents recorded between 1995 and 2007, 96% were of the ‘excursion’ type.
The U.S. FAA publishes an lengthy annual report on runway safety issues, available from the FAA website here. New systems designed to improve runway safety, such as Airport Movement Area Safety System (AMASS) and Runway Awareness and Advisory System (RAAS), are discusssed in the report. AMASS prevented the serious near-collision in the 2007 San Francisco International Airport runway incursion.
Accidents and incidents
• List of airship accidents
• Lists of aviation accidents
• Aviation accidents and incidents
• Flight recorder, includes Flight data recorder and Cockpit voice recorder
Airservices Australia ADS-B initiative is one of the major implementation programs in this field. This initiative will facilitate the certification of this new technology allowing further implementation.
The two core satellite constellations are the Global Positioning System (GPS) of the USA and the Global Navigation Satellite System (GLONASS) of Russia. The third largest constellations would be Europe’s GALILEO when it becomes fully operational. These systems provide independent capabilities and can be used in combination with future core constellations and augmentation systems. Signals from core satellite are received by ground reference stations and any errors in the signals are identified. Each station in the network relays the data to area-wide master stations where correction information for specific geographical areas is computed. The correction message is prepared and uplinked to a geostationary communication satellite (GEO) via a ground uplink station. This message is broadcast to receivers on board aircraft flying within the broadcast coverage area of the System. The system is known in the USA as WAAS (Wide Area Augmentation System), in Europe as EGNOS (European Geostationary Navigation Overlay System), in Japan as MSAS (MTSAT Satellite Based Augmentation System) and in India as GAGAN (GPS Aided Geo Augmented Navigation).
The system employs various techniques to correct equatorial anomalies. The advantage of the system is, it is Global in scope and it has the potential to support all phases of flight providing a seamless global navigation guidance. This could eliminate the need for a variety of ground and airborne systems that were designed to meet specific requirements for certain phases of flight. Standard and Recommended Practices for the air traffic management based on a global navigation satellite system are developed by ICAO (International Civil Aviation Organization). Thus the system has to meet ICAO standards to become operational.
Air Safety
Air safety is a term encompassing the theory, investigation and categorization of flight failures, and the prevention of such failures through regulation, education and training. It can also be applied in the context of campaigns that inform the public as to the safety of air travel.
Institutions
Certification
In most countries, civil aircraft have to be certified by the Civil Aviation Authority (CAA) to be allowed to fly. The major aviation authorities worldwide are the US Federal Aviation Administration (FAA) the European Aviation Safety Agency (EASA) (which provides regulatory advice to the European Union and to a degree supplanted the regulatory bodies of member countries). FAA and EASA are, in particular, primarily responsible for the certification of the airliners from the two major manufacturers, Boeing and Airbus. Aircraft are certified against gudielines set out in the code for each CAA. Those codes are very similar and differ primarily in equipment and environmental standards. Regulations on maintenance, repair and operation provide further direction to the owners of the aircraft so that the aircraft continues to meet design standards.
United States
During the 1920s, the first laws were passed in the USA to regulate civil aviation. Of particular significance was the Air Commerce Act 1926, which required pilots and aircraft to be examined and licensed, for accidents to be properly investigated, and for the establishment of safety rules and navigation aids, under the Aeronautics Branch of the Department of Commerce.
Despite this, in 1926 and 1927 there were a total of 24 fatal commercial airline crashes, a further 16 in 1928, and 51 in 1929 (killing 61 people), which remains the worst year on record at an accident rate of about 1 for every 1,000,000 miles flown. Based on the current numbers flying, this would equate to 7,000 fatal incidents per year.
The fatal incident rate has declined steadily ever since, and, since 1997 the number of fatal air accidents has been no more than 1 for every 2,000,000,000 person-miles flown (e.g., 100 people flying a plane for 1000 miles counts as 100,000 person-miles, making it comparable with methods of transportation with different numbers of passengers, such as one person driving a car for 100,000 miles, which is also 100,000 person-miles), making it one of the safest modes of transportation, as measured by distance traveled.
A disproportionate number of all U.S. aircraft crashes occur in Alaska, largely as a result of severe weather conditions. Between 1990-2006 there were 1441 commuter and air taxi crashes in the U.S. of which 373 (26%) were fatal, resulting in 1063 deaths (142 occupational pilot deaths). Alaska accounted for 513 (36%) of the total U.S. crashes.
Another aspect of safety is protection from attack. The terrorist attacks of 2001 are not counted as accidents. However, even if they were counted as accidents they would have added only about 2 deaths per 2,000,000,000 person-miles. Unfortunately, only 2 months later, American Airlines Flight 587 crashed in Queens, NY, killing 256 people, including 5 on the ground, causing 2001 to show a very high fatality rate. Even so, the rate that year including the attacks (estimated here to be about 4 deaths per 1,000,000,000 person-miles), may be relatively safe compared to some other forms of transport, if measured by distance traveled.
Safety improvements have resulted from improved aircraft design, engineering and maintenance, the evolution of navigation aids, and safety protocols and procedures.
It is often reported that air travel is the safest in terms of deaths per passenger mile. The National Transportation Safety Board (2006) reports 1.3 deaths per hundred million vehicle miles for travel by car, and 1.7 deaths per hundred million vehicle miles for travel by air. These are not passenger miles. If an airplane has 100 passengers, then the passenger miles are 100 times higher, making the risk 100 times lower. The number of deaths per passenger mile on commercial airlines between 1995 and 2000 is about 3 deaths per 10 billion passenger miles.
Navigation Aids and Instrument Flight
One of the first navigation aids to be introduced (in the USA in the late 1920s) was airfield lighting to assist pilots to make landings in poor weather or after dark. The Precision Approach Path Indicator was developed from this in the 1930s, indicating to the pilot the angle of descent to the airfield. This later became adopted internationally through the standards of the International Civil Aviation Organization (ICAO).
In 1929 Jimmy Doolittle developed instrument flight.
With the spread of radio technology, several experimental radio based navigation aids were developed from the late 1920s onwards. These were most successfully used in conjunction with instruments in the cockpit in the form of Instrument landing systems (ILS), first used by a scheduled flight to make a landing in a snowstorm at Pittsburgh in 1938. A form of ILS was adopted by the ICAO for international use in 1949.
Following the development of radar in World War II, it was deployed as a landing aid for civil aviation in the form of Ground-controlled approach (GCA) systems, joined in 1948 by distance measuring equipment (DME), and in the 1950s by airport surveillance radar as an aid to air traffic control. VHF omnidirectional range (VOR) became the predominate means of route navigation during the 1960s superseding the Non-directional beacon (NDB). The ground based VOR stations were often co-located with DME, so that pilots could know both their radials in degrees with respect to north to, and their slant range distance to, that beacon.
All of the ground-based navigation aids are being supplemented by satellite-based aids like Global Positioning System (GPS), which make it possible for aircrews to know their position with great precision anywhere in the world. With the arrival of Wide Area Augmentation System (WAAS), GPS navigation has become accurate enough for vertical (altitude) as well as horizontal use, and is being used increasingly for instrument approaches as well as en-route navigation. However, since the GPS constellation is a single point of failure that can be switched off by the U.S. military in time of crisis, onboard Inertial Navigation System (INS) or ground-based navigation aids are still required for backup.
Air safety topics
Lightning
Boeing studies have shown that airliners are struck by lightning on average of twice per year. While the “flash and bang” is startling to the passengers and crew, aircraft are able to withstand normal lightning strikes.
The dangers of more powerful positive lightning were not understood until the destruction of a glider in 1999.[5] It has since been suggested that positive lightning may have caused the crash of Pan Am Flight 214 in 1963. At that time aircraft were not designed to withstand such strikes, since their existence was unknown at the time standards were set.
The effects of normal lightning on traditional metal-covered aircraft are well understood and serious damage from a lightning strike on an airplane is rare. However, as more and more aircraft, like the upcoming Boeing 787, whose whole exterior is made of non-conducting composite materials take to the skies, additional design effort and testing must be made before certification authorities will permit these aircraft in commercial service.
Ice and Snow
Snowy and icy conditions are frequent contributors to airline accidents. The December 8, 2005 accident where Southwest Airlines Flight 1248 slid off the end of the runway in heavy snow conditions is just one of many examples. Just as on a road, ice and snow buildup can make braking and steering difficult or impossible.
The icing of wings is another problem and measures have been developed to combat it. Even a small amount of ice or coarse frost can greatly decrease the ability of a wing to develop lift. This could prevent an aircraft from taking off. If ice builds up during flight the result can be catastrophic as evidenced by the crash of American Eagle Flight 4184 (an ATR 72 aircraft) near Roselawn, Indiana on October 31, 1994, killing 68, or Air Florida Flight 90.
Airlines and airports ensure that aircraft are properly de-iced before takeoff whenever the weather threatens to create icing conditions. Modern airliners are designed to prevent ice buildup on wings, engines, and tails (empennage) by either routing heated air from jet engines through the leading edges of the wing, tail, and inlets, or on slower aircraft, by use of inflatable rubber “boots” that expand and break off any accumulated ice.
Finally, airline dispatch offices keep watch on weather along the routes of their flights, helping the pilots avoid the worst of inflight icing conditions. Pilots can also be equipped with an ice detector in order to leave icy areas they have flown into.
Engine Failure
Although aircraft are now designed to fly even after the failure of one or more aircraft engines, the failure of the second engine on one side for example is obviously serious. Losing all engine power is even more serious, as illustrated by the 1970 Dominicana DC-9 air disaster, when fuel contamination caused the failure of both engines. To have an emergency landing site is then very important.
In the 1983 Gimli Glider incident, an Air Canada flight suffered fuel exhaustion during cruise flight, forcing the pilot to glide the plane to an emergency deadstick landing. The automatic deployment of the ram air turbine maintained the necessary hydraulic pressure to the flight controls, so that the pilot was able to land with only a minimal amount of damage to the plane, and minor (evacuation) injuries to a few passengers.
The ultimate form of engine failure, physical separation, occurred in 1979 when a complete engine detached from American Airlines Flight 191, causing damage to the aircraft and loss of control.
Metal Fatigue
Metal fatigue has caused failure either of the engine (for example in the January 8, 1989 Kegworth air disaster), or of the aircraft body, for example the De Havilland Comets in 1953 and 1954 and Aloha Airlines Flight 243 in 1988. Now that the subject is better understood, rigorous inspection and nondestructive testing procedures are in place.
Delamination
Composite materials consist of layers of fibers embedded in a resin matrix. In some cases, especially when subjected to cyclic stress, the fibers may tear off the matrix, the layers of the material then separate from each other - a process called delamination, and form a mica-like structure which then falls apart. As the failure develops inside the material, nothing is shown on the surface; instrument methods (often ultrasound-based) have to be used.
Aircraft have developed delamination problems, but most were discovered before they caused a catastrophic failure. Delamination risk is as old as composite material. Even in the 1940s, several Yakovlev Yak-9s experienced delamination of plywood in their construction.
Stalling
Stalling an aircraft (increasing the angle of attack to a point at which the wings fail to produce enough lift) is a danger, but is normally recoverable. Devices have been developed to warn the pilot as stall approaches. These include stall warning horns (now standard on virtually all powered aircraft), stick shakers and voice warnings. Two stall-related airline accidents were British European Airways Flight 548 in 1972, and the United Airlines Flight 553 crash, while on approach to Chicago Midway International Airport, also in 1972.
Fire
Safety regulations control aircraft materials and the requirements for automated fire safety systems. Usually these requirements take the form of required tests. The tests measure flammability and the toxicity of smoke. When the tests fail, they fail on a prototype in an engineering laboratory, rather than in an aircraft.
Fire on board the aircraft, and more especially the toxic smoke generated, have been the cause of incidents. An electrical fire on Air Canada Flight 797 in 1983 caused the deaths of 23 of the 46 passengers, resulting in the introduction of floor level lighting to assist people to evacuate a smoke-filled aircraft. Two years later a fire on the runway caused the loss of 55 lives, 48 from the effects of incapacitating and subsequently lethal toxic gas and smoke, in the 1985 British Airtours Flight 28M. This incident raised serious concerns relating to survivability, something that prior to 1985 had not been studied in such detail. The swift incursion of the fire into the fuselage and the layout of the aircraft impaired passengers’ ability to evacuate, with areas such as the forward galley area becoming a bottle-neck for escaping passengers, with some dying very close to the exits. A large amount of research into evacuation and cabin and seating layouts was carried at Cranfield Institute to try to measure what makes a good evacuation route which led to the seat layout by Overwing exits being changed by mandate and the examination of evacuation requirements relating to the design of galley areas. The use of smoke hoods or misting systems were also examined although both were rejected.
The cargo holds of most airliners are equipped with “fire bottles” (essentially remote-controlled fire extinguishers) to combat a fire that might occur in with the baggage and freight below the passenger cabin. This was due to an accident in 1996. In May of that year ValuJet Airlines Flight 592 crashed into the Florida Everglades a few minutes after takeoff after a fire broke out in the forward cargo hold. All 110 aboard were killed.
The investigation determined that improperly packaged chemical oxygen generators (used for the drop-down oxygen masks in the aircraft cabin) had been loaded into the cargo hold. Oxygen generators produce oxygen through a chemical reaction that also generates hundreds of degrees of heat. When installed for use in the ceiling above the passenger seats they are surrounded by heat-resistant shielding and present no fire hazard. On this flight they had been put loosely into a cardboard box for shipment from a maintenance facility.
It is likely that one or more of the generators ignited, during or immediately after takeoff, producing an oxygen-rich environment. The cardboard box containing the generators would have quickly caught fire from the heat of the ignited generator. The fire spread to an aircraft tire that was also carried in the hold. Ordinarily the fire would have smothered itself, because of the airtight design of that cargo compartment. But the oxygen generators kept feeding oxygen to the fire, defeating the smothering design of the McDonnell Douglas DC-9 cargo hold. The fire rapidly burned through the passenger cabin floor, incapacitating all aboard with smoke and poisonous gases very quickly. The pilots, although having smoke masks and separate oxygen supplies, had no hope of maintaining control as control cables and electrical wiring burned through.
The maintenance facility (SabreTech) was subjected to large fines and ValuJet, due to this accident and other irregularities, was grounded. The airline reemerged as a smaller airline and eventually merged with AirTran Airways, a smaller carrier. Adopting the acquired airline’s name, the airline has since provided safe service. For the airline industry, rules for the shipment of oxygen generators was severely restricted and cargo holds on larger airliners were required to have “fire bottles” installed.
At one time fire fighting foam paths were laid down before an emergency landing, but the practice was considered only marginally effective, and concerns about the depletion of fire fighting capability due to pre-foaming led the United States FAA to withdraw its recommendation in 1987.
Bird Strike
Bird strike is an aviation term for a collision between a bird and an aircraft. It is a common threat to aircraft safety and has caused a number of fatal accidents. In 1988 an Ethiopian Airlines Boeing 737 sucked pigeons into both engines during take-off and then crashed in an attempt to return to the Bahir Dar airport; of the 104 people aboard, 35 died and 21 were injured. In another incident in 1995, a Dassault Falcon 20 crashed at a Paris airport during an emergency landing attempt after sucking lapwings into an engine, which caused an engine failure and a fire in the airplane fuselage; all 10 people on board were killed. A bird strike is suspected as causing the engines to fail on US Airways 1549 that crash landed onto the Hudson River.
Modern jet engines have the capability of surviving an ingestion of a bird. Small fast planes, such as military jet fighters, are at higher risk than big heavy multi-engine ones. This is due to the fact that the fan of a high-bypass turbofan engine, typical on transport aircraft, acts as a centrifugal separator to force ingested materials (birds, ice, etc.) to the outside of the fan’s disc.
As a result, such materials go through the relatively unobstructed bypass duct, rather than through the core of the engine, which contains the smaller and more delicate compressor blades. Military aircraft designed for high-speed flight typically have pure turbojet, or low-bypass turbofan engines, increasing the risk that ingested materials will get into the core of the engine to cause damage.
The highest risk of the bird strike is during the takeoff and landing, in low altitudes, which is in the vicinity of the airports. Some airports use active countermeasures, ranging from a person with a shotgun through recorded sounds of predators to employing falconers. Poisonous grass can be planted that is not palatable to birds, nor to insects that attract insectivorous birds. Passive countermeasures involve sensible land-use management, avoiding conditions attracting flocks of birds to the area (eg. landfills). Another tactic found effective is to let the grass at the airfield grow taller (approximately 12 inches (30 centimetres)) as some species of birds won’t land if they cannot see one another.
Ground Damage
Aircraft are occasionally damaged by ground equipment at the airport. In the act of servicing the aircraft between flights a great deal of ground equipment must operate in close proximity to the fuselage and wings. Occasionally the aircraft gets bumped or worse.
Damage may be in the form of simple scratches in the paint or small dents in the skin. However, because aircraft structures (including the outer skin) play such a critical role in the safe operation of a flight, all damage is inspected, measured and possibly tested to ensure that any damage is within safe tolerances. A dent that may look no worse than common “parking lot damage” to an automobile can be serious enough to ground an airplane until a repair can be made.
An example of the seriousness of this problem was the December 26, 2005 depressurization incident on Alaska Airlines flight 536. During ground services a baggage handler hit the side of the aircraft with a tug towing a train of baggage carts. This damaged the metal skin of the aircraft.
This damage was not reported and the plane departed. Climbing through 26,000 feet (7,925 metres) the damaged section of the skin gave way due to the growing difference in pressure between the inside of the aircraft and the outside air. The cabin depressurized with a bang, frightening all aboard and necessitating a rapid descent back to denser (breathable) air and an emergency landing. Post landing examination of the fuselage revealed a
12 in × 6 in (30 cm × 15 cm) hole between the middle and forward cargo doors on the right side of the airplane.
The three pieces of ground equipment that most frequently damage aircraft are the passenger boarding bridge, catering trucks, and cargo “beltloaders.” However, any other equipment found on an airport ramp can damage an aircraft through careless use, high winds, mechanical failure, and so on.
The generic industry colloquial term for this damage is “ramp rash”, or “hangar rash”.
Volcanic Ash
Plumes of volcanic ash near active volcanoes present a risk especially for night flights. The ash is hard and abrasive and can quickly cause significant wear on the propellers and turbocompressor blades, and scratch the cabin windows, impairing visibility.
It contaminates fuel and water systems, can jam gears, and can cause a flameout of the engines. Its particles have low melting point, so they melt in the combustion chamber and the ceramic mass then sticks on the turbine blades, fuel nozzles, and the combustors, which can lead to a total engine failure. It can get inside the cabin and contaminate everything there, and can damage the airplane electronics.
There are many instances of damage to jet aircraft from ash encounters. In one of them in 1982, British Airways Flight 009 flew through an ash cloud, lost all four engines, and descended from 36,000 ft (11,000 m) to only 12,000 ft (3,700 m) before the flight crew managed to restart the engines.
With the growing density of air traffic, encounters like this are becoming more common. In 1991 the aviation industry decided to set up Volcanic Ash Advisory Centers (VAACs), one for each of 9 regions of the world, acting as liaisons between meteorologists, volcanologists, and the aviation industry.
Human Factors
Human factors including pilot error are another potential danger, and currently the most common factor of aviation crashes. Much progress in applying human factors to improving aviation safety was made around the time of World War II by people such as Paul Fitts and Alphonse Chapanis.
However, there has been progress in safety throughout the history of aviation, such as the development of the pilot’s checklist in 1937. Pilot error and improper communication are often factors in the collision of aircraft. This can take place in the air (1978 Pacific Southwest Airlines Flight 182) (TCAS) or on the ground (1977 Tenerife disaster) (RAAS).
The ability of the flight crew to maintain situational awareness is a critical human factor in air safety. Human factors training is available to general aviation pilots and called single pilot resource management training.
Failure of the pilots to properly monitor the flight instruments resulted in the crash of Eastern Air Lines Flight 40 in 1972 (CFIT), and error during take-off and landing can have catastrophic consequences, for example cause the crash of Prinair Flight 191 on landing, also in 1972.
Rarely, flight crew members are arrested or subject to disciplinary action for being intoxicated on the job. In 1990, three Northwest Airlines crew members were sentenced to jail for flying from Fargo, North Dakota to Minneapolis-Saint Paul International Airport while drunk.
In 2001, Northwest fired a pilot who failed a breathalyzer test after flying from San Antonio, Texas to Minneapolis-Saint Paul. In July 2002, two America West Airlines pilots were arrested just before they were scheduled to fly from Miami, Florida to Phoenix, Arizona because they had been drinking alcohol.
The pilots have been fired from America West and the FAA revoked their pilot’s licenses. As of 2005 they await trial in a Florida court. The incident created a public relations problem and America West has become the object of many jokes about drunk pilots. At least one fatal airliner accident involving drunk pilots has occurred when Aero Flight 311 crashed killing all 25 on board in 1961, which underscores the role that poor human choices can play in air accidents.
Human factors incidents are not limited to errors by the pilots. The failure to close a cargo door properly on Turkish Airlines Flight 981 in 1974 resulted in the loss of the aircraft - however the design of the cargo door latch was also a major factor in the incident.
In the case of Japan Airlines Flight 123, improper maintenance resulted in the loss of the vertical stabilizer.
Controlled flight into terrain
Controlled flight into terrain is a class of accident in which an undamaged aircraft is flown, under control, into terrain. CFIT accidents typically are a result of pilot error or of navigational system error. Some pilots, convinced that advanced electronic navigation systems such as GPS and inertial guidance systems (inertial navigation system or INS) coupled with flight management system computers, or over-reliance on them, are partially responsible for these accidents, have called CFIT accidents “computerized flight into terrain”.
Failure to protect Instrument Landing System critical areas can also cause controlled flight into terrain. Crew awareness and monitoring of navigational systems can prevent or eliminate CFIT accidents. Crew Resource Management is a modern method now widely used to improve the human factors of air safety. The Aviation Safety Reporting System, or ASRS is another.
Other technical aids can be used to help pilots maintain situational awareness. A ground proximity warning system is an on-board system that will alert a pilot if the aircraft is about to fly into the ground. Also, air traffic controllers constantly monitor flights from the ground and at airports.
Terrorism
Terrorism can also be considered a human factor. Crews are normally trained to handle hijack situations. Prior to the September 11, 2001 attacks, hijackings involved hostage negotiations. After the September 11, 2001 attacks, stricter airport security measures are in place to prevent terrorism using a Computer Assisted Passenger Prescreening System, Air Marshals, and precautionary policies. In addition, counter-terrorist organizations monitor potential terrorist activity.
Although most air crews are screened for psychological fitness, some may take suicidal actions. In the case of EgyptAir Flight 990, it appears that the first officer (co-pilot) deliberately dived his aircraft into the Atlantic Ocean while the captain was away from his station, in 1999 off Nantucket, Massachusetts. Motivations are unclear, but recorded inputs from the black boxes showed no mechanical problem, no other aircraft in the area, and was corroborated by the cockpit voice recorder.
The use of certain electronic equipment is partially or entirely prohibited as it may interfere with aircraft operation, such as causing compass deviations.
Use of personal electronic devices and calculators may be prohibited when an aircraft is below 10,000', taking off, or landing. The American Federal Communications Commission (FCC) prohibits the use of a cell phone on most flights, because in-flight usage creates problems with ground-based cells.
There is also concern about possible interference with aircraft navigation systems, although that has never been proven to be a non-serious risk on airliners. A few flights now allow use of cell phones, where the aircraft have been specially wired and certified to meet both FAA and FCC regulations.
Attack by Hostile Country
Aircraft, whether civilian passenger planes or military aircraft, are sometimes attacked in both peacetime and war. One notable example of this is the Sept. 1, 1983 downing by the Soviet Union of Korean Air Lines Flight 007, carrying 269 people (including a sitting U.S. Congressman Larry McDonald).
Airport Design
Airport design and location can have a big impact on air safety, especially since some airports such as Chicago Midway International Airport were originally built for propeller planes and many airports are in congested areas where it is difficult to meet newer safety standards.
For instance, the FAA issued rules in 1999 calling for a runway safety area, usually extending 500 feet (150 m) to each side and 1,000 feet (300 m) beyond the end of a runway. This is intended to cover ninety percent of the cases of an aircraft leaving the runway by providing a buffer space free of obstacles.
Since this is a recent rule, many airports do not meet it. One method of substituting for the 1,000 feet (300 m) at the end of a runway for airports in congested areas is to install an Engineered materials arrestor system, or EMAS. These systems are usually made of a lightweight, crushable concrete that absorbs the energy of the aircraft to bring it to a rapid stop. They have stopped three aircraft (as of 2005) at JFK Airport.
Infection
On an airplane, hundreds of people sit in a confined space for extended periods of time, which increases the risk of transmission of airborne infections.
For this reason, airlines place restrictions on the travel of passengers with known airborne contagious diseases (e.g. tuberculosis). During the severe acute respiratory syndrome (SARS) epidemic of 2003, awareness of the possibility of acquisition of infection on a commercial aircraft reached its zenith when on one flight from Hong Kong to Beijing, 16 of 120 people on the flight developed proven SARS from a single index case.
There is very limited research done on contagious diseases on aircraft. The two most common respiratory pathogens to which air passengers are exposed are parainfluenza and influenza. Certainly, the flight ban imposed following the attacks of September 11, 2001 restricted the ability of influenza to spread around the globe, resulting in a much milder influenza season that year, and the ability of influenza to spread on aircraft has been well documented.
There is no data on the relative contributions of large droplets, small particles, close contact, surface contamination, and certainly no data on the relative importance of any of these methods of transmission for specific diseases, and therefore very little information on how to control the risk of infection. There is no standardisation of air handling by aircraft, installation of HEPA filters or of hand washing by air crew, and no published information on the relative efficacy of any of these interventions in reducing the spread of infection.
Emergency Airplane Evacuations
According to a 2000 report by the National Transportation Safety Board, emergency airplane evacuations happen about once every 11 days in the U.S. While some situations are extremely dire, such as when the plane is on fire, in many cases the greatest challenge for passengers can be the use of the airplane slide.
In a TIME article on the subject, Amanda Ripley reported that when a new supersized Airbus A380 underwent mandatory evacuation tests in 2006, 33 of the 873 evacuating volunteers got hurt. While the evacuation was generally considered a success, one volunteer suffered a broken leg, while the remaining 32 received slide burns. Such accidents are common. In her article, Ripley provides tips on how to make it down the airplane slide without injury.
Runway Safety
Several terms fall under the flight safety topic of of runway safety, including incursion, excursion, and confusion.
Runway excursion is an incident involving only a single aircraft, where it makes an inappropriate exit from the runway. This can happen because of pilot error, poor weather, or a fault with the aircraft. Overrun is a type of excursion where the aircraft is unable to stop before the end of the runway. A recent example of such an event is Air France Flight 358 in 2005. Further examples can be found in the overruns category.
Runway event is another term for a runway accident.
Runway incursion involves a first aircraft, as well as a second aircraft, vehicle, or person. It is defined by the U.S. FAA as: “Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft.”
Runway confusion involves a single aircraft, and is used to describe the error when the aircraft makes “the unintentional use of the wrong runway, or a taxiway, for landing or take-off”. An example of a “Runway confusion” incident can be Comair Flight 5191.
Runway excursion is the most frequent type of landing accident, slightly ahead of runway incursion. For runway accidents recorded between 1995 and 2007, 96% were of the ‘excursion’ type.
The U.S. FAA publishes an lengthy annual report on runway safety issues, available from the FAA website here. New systems designed to improve runway safety, such as Airport Movement Area Safety System (AMASS) and Runway Awareness and Advisory System (RAAS), are discusssed in the report. AMASS prevented the serious near-collision in the 2007 San Francisco International Airport runway incursion.
Accidents and incidents
• List of airship accidents
• Lists of aviation accidents
• Aviation accidents and incidents
• Flight recorder, includes Flight data recorder and Cockpit voice recorder
Area Control Center
In air traffic control, an Area Control Center (ACC), also known as a Center, is a facility responsible for controlling instrument flight rules aircraft en route in a particular volume of airspace (a Flight Information Region) at high altitudes between airport approaches and departures. In the United States, such a Center is referred to as an Air Route Traffic Control Center (ARTCC).
A Center typically accepts traffic from, and ultimately passes traffic to, the control of a Terminal Control Center or of another Center. Most Centers are operated by the national governments of the countries in which they are located. The general operations of Centers world-wide, and the boundaries of the airspace each Center controls, are governed by the ICAO.
In some cases, the function of an Area Control Center and a Terminal Control Center are combined in a single facility. For example, NATS combines the London Terminal Control Centre (LTCC) and London Area Control Centre (LACC) in Swanwick in the UK.
FAA Definition
The United States Federal Aviation Administration defines an ARTCC as: [a] facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace, principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft. An ARTCC is the U.S. equivalent of an Area Control Center (ACC).
Subdivision of Airspace into Sectors
The Flight Information Region controlled by a Center may be further administratively subdivided into sectors; each sector may use a distinct set of communications frequencies and personnel. An aircraft passing from one sector to another may be handed off and requested to change frequencies to contact the next sector controller. Sector boundaries are specified by an aeronautical chart.
Center Operations
Air traffic controllers working within a Center communicate via radio with pilots of instrument flight rules aircraft passing through the Center’s airspace. A Center’s communication frequencies (typically in the very high frequency amplitude modulation aviation bands, 118 MHz to 137 MHz, for overland control) are published in aeronautical charts and manuals, and will also be announced to a pilot by the previous controller during a hand-off.
In addition to radios to communicate with aircraft, Center controllers have access to communication links with other Centers and TRACONs. In the United States, Centers are electronically linked through the National Airspace System, which allows nationwide coordination of traffic flow to manage congestion. Centers in the United States also have electronic access to nationwide radar data.
Controllers use radar to monitor the progress of flights and instruct aircraft to perform course adjustments as needed to maintain separation from other aircraft. Aircraft with which a Center has made radar contact can be readily distinguished by their transponders. Pilots may also request altitude adjustments or course changes to avoid turbulence or adverse weather conditions.
Controllers can assign routing relative to location fixes derived from latitude and longitude, or from radionavigation beacons such as VORs. See also Airway; VORs, Airways and the Enroute Structure.
Typically, Centers have advanced notice of a plane’s arrival and intentions from its prefiled flight plan.
Oceanic Air Traffic Control
Some Centers have ICAO-designated responsibility for airspace located over an ocean such as ZOA, the majority of which is international airspace.
Because substantial volumes of oceanic airspace lie beyond the range of ground-based radars, oceanic airspace controllers have to estimate the position of an airplane from pilot reports and computer models (procedural control), rather than observing the position directly (radar control, also known as positive control). Pilots flying over an ocean can determine their own positions accurately using the Global Positioning System and can supply periodic updates to a Center. See also Air traffic control: Radar Coverage.
A Center’s control service for an oceanic FIR may be operationally distinct from its service for a domestic overland FIR over land, employing different communications frequencies, controllers, and a different ICAO code.
Pilots typically use high frequency radio instead of very high frequency radio to communicate with a Center when flying over the ocean, because of HF’s relatively greater propagation over long distances.
Air Traffic Control Websites
A Center typically accepts traffic from, and ultimately passes traffic to, the control of a Terminal Control Center or of another Center. Most Centers are operated by the national governments of the countries in which they are located. The general operations of Centers world-wide, and the boundaries of the airspace each Center controls, are governed by the ICAO.
In some cases, the function of an Area Control Center and a Terminal Control Center are combined in a single facility. For example, NATS combines the London Terminal Control Centre (LTCC) and London Area Control Centre (LACC) in Swanwick in the UK.
FAA Definition
The United States Federal Aviation Administration defines an ARTCC as: [a] facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace, principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft. An ARTCC is the U.S. equivalent of an Area Control Center (ACC).
Subdivision of Airspace into Sectors
The Flight Information Region controlled by a Center may be further administratively subdivided into sectors; each sector may use a distinct set of communications frequencies and personnel. An aircraft passing from one sector to another may be handed off and requested to change frequencies to contact the next sector controller. Sector boundaries are specified by an aeronautical chart.
Center Operations
Air traffic controllers working within a Center communicate via radio with pilots of instrument flight rules aircraft passing through the Center’s airspace. A Center’s communication frequencies (typically in the very high frequency amplitude modulation aviation bands, 118 MHz to 137 MHz, for overland control) are published in aeronautical charts and manuals, and will also be announced to a pilot by the previous controller during a hand-off.
In addition to radios to communicate with aircraft, Center controllers have access to communication links with other Centers and TRACONs. In the United States, Centers are electronically linked through the National Airspace System, which allows nationwide coordination of traffic flow to manage congestion. Centers in the United States also have electronic access to nationwide radar data.
Controllers use radar to monitor the progress of flights and instruct aircraft to perform course adjustments as needed to maintain separation from other aircraft. Aircraft with which a Center has made radar contact can be readily distinguished by their transponders. Pilots may also request altitude adjustments or course changes to avoid turbulence or adverse weather conditions.
Controllers can assign routing relative to location fixes derived from latitude and longitude, or from radionavigation beacons such as VORs. See also Airway; VORs, Airways and the Enroute Structure.
Typically, Centers have advanced notice of a plane’s arrival and intentions from its prefiled flight plan.
Oceanic Air Traffic Control
Some Centers have ICAO-designated responsibility for airspace located over an ocean such as ZOA, the majority of which is international airspace.
Because substantial volumes of oceanic airspace lie beyond the range of ground-based radars, oceanic airspace controllers have to estimate the position of an airplane from pilot reports and computer models (procedural control), rather than observing the position directly (radar control, also known as positive control). Pilots flying over an ocean can determine their own positions accurately using the Global Positioning System and can supply periodic updates to a Center. See also Air traffic control: Radar Coverage.
A Center’s control service for an oceanic FIR may be operationally distinct from its service for a domestic overland FIR over land, employing different communications frequencies, controllers, and a different ICAO code.
Pilots typically use high frequency radio instead of very high frequency radio to communicate with a Center when flying over the ocean, because of HF’s relatively greater propagation over long distances.
Air Traffic Control Websites
- Air Traffic Control & Business Systems GmbH AC-B GmbH develops and cares for message switching systems as well as business systems within the air traffic control area.
- Air Traffic Control in The Netherlands Information, frequencies, sound, pictures maps. Very good list of ATC-related links.
- Air Traffic Control Sri Lanka This site is dedicated to all aspects civil aviation, especially air traffic control, air traffic engineering, radar control, auto pilot operation, and satellite guided air navigation.
- Air Traffic Control Webring An international ATC Webring. ATC and Aviation professionals or aficionados are all welcome to join.
- Air Traffic Soup This blog has ingredients of aviation and an air traffic controller perpective. It was started by an air traffic controller working at Chicago Executive Air Traffic Control Tower to help others get an idea and feel for what the ATC profession is all about.
- ATCeaBLOG Air Traffic Control fact and opinion updated regularly.
- ATC News Air traffic control news headlines - updated daily.
- atcosonline A community-based site for air traffic controllers with forum, user blogs, news, links.
- ATCstuff.com An online store with gifts and items for Air Traffic Controllers.
- Aviation On-line Radio Network Live events, sound bytes.
- Checkoutparty.com A site for air traffic control
- students in Canada. Also has a nice collection of tower pictures.
- David McMillan’s ATC Home Page The personal page of an air traffic controller at Melbourne Centre, Victoria, Australia.
- DFW Tower.com This is an aviation website for DFW and North Texas. While the site is dedicated to the aviation enthusiast, they hope to have something for everybody. Whether you are simply checking the weather, the status of your flight, or are curious about DFW, this is the place for you.
- The FAA Follies This blog offers the inside opinion of one air traffic controller.
- FightGridlockNow.gov The National Strategy to Reduce Congestion on America’s Transportation Network (the “Congestion Initiative”) seeks solutions to ease transportation system congestion, including aviation congestion.
- Flight Service Sigmet This blog provides a running commentary by an Air Traffic Controller on the present state of Flight Service, with specific focus on the recent contracting-out to Lockheed Martin.
- Fort Worth Air Route Traffic Control Center FAQs, training, pilots info, other general information.
- Local 1 - Air Traffic Control Simulation A freeware ATC tower simulation.
- Local5454 - SquawkIdent A communication portal for Canadian Air Traffic Controllers with a forum, links to aviation news, and live ATC feeds.
- The Main Bang By a past president of the National
- Air Traffic Controllers Association, now retired after
- more than 29 years of government service. He currently does freelance consulting, serves as an expert witness in judicial proceedings involving the FAA, and writes extensively. The blog covers current aviation and FAA issues.
- My Life And Air Traffic Control An Australian Air Traffic Controller writes about his job, how to be an air traffic controller, how much you get paid, and other topics.
- National Air Traffic Controllers Association NATCAnet NATCAnet Web Pages, membership, services, contact information, links, chat.
- National Air Traffic Services Ltd UK aerodrome information (by ICAO designation or airport name), navigation warnings, daily bulletins.
- National Air Traffic Services (NATS) The UK’s air traffic service provides safety by ensuring aircraft flying in UK airspace, and over the eastern part of the North Atlantic, are safely separated.
- NAV CANADA The Gander Automated Air Traffic System (GAATS) oceanic air traffic system based in Gander, Newfoundland is dedicated to the North Atlantic airspace.
- The Potomac Current and Undertow A blog from, for, about, and to the air traffic controllers at the Potomac TRACON. Visitors are invited to share in the exchange of the events posted in the blog.
- Professional Air Traffic Controllers Organization PATCO is an independent labor union, certified by the NLRB, and representing air traffic controllers in matters relating to wages, hours, and other terms and conditions of employment. PATCO currently represents contract tower controllers working for RVA, Midwest, and SERCO with tower locations in New Jersey, Texas, Montana, Georgia, Connecticut, Indiana, and Wisconsin. PATCO membership also includes hundreds of PATCO strikers.
- Professional Women Controllers, Inc. PWC is an association of air traffic control specialists (both men and women). While membership is predominantly composed of controllers within the USA, the international membership base is expanding. The webpage is used to facilitate the networking of persons in the air traffic control professional field, both within and outside the United States, and to keep members informed on issues, career opportunities, and activities.
- Readback - VHF Air Traffic Control Monitoring Mailing List A mailing list dedicated exclusively to the reception and appreciation of civil Air Traffic Control voice communications in the VHF air-band. Emphasis of postings should be on logs of voice radio communications received on civil VHF aviation frequencies that can be qualified as out of the ordinary.
- Rhein Radar Controllers Association A site for those working as air traffic controllers at the DFS Air Traffic Control Center Karlsruhe (Germany), the Karlsruhe UAC (Upper Area Control Center).
- Smart Skies This national campaign is led by the airlines of the Air Transport Association, and advocates modernization of the U.S. air traffic control system (ATC) and its funding mechanisms.
- TheTRACON.com Extensive links list: NATCA and other Union pages, towers, centers, flight service stations, controller pages, FAA pages, live ATC. By the Chicago local of the National Air Traffic Controllers Association AFL-CIO (NATCA).
- Traffico-Aereo.it The 1st private Italian ATC related site.
- Yahoo! Air Traffic Control
- Live Air Traffic Control
- Air Traffic Control Bankstown Airport Live Air Traffic Control radio conversations from Bankstown Tower, Sydney, Australia.
- ATCMonitor.com Live monitoring of the busiest en route Air Traffic Control Corridor in the world: the Northeast Atlanta Macey Womac Arrival servicing the Atlanta Hartsfield Jackson International Airport, Atlanta Georgia USA. Designed to educate the public about en route air traffic control centers. For the curious public, travel enthusiasts, pilots, flight simmers, student air traffic controllers, aviation retirees, air traffic controllers, or anyone with an interest in what goes on in en route air traffic control centers. Streaming audio and video.
- CyberAir Airpark Chicago Approach Listen to live transmissions (using RealAudio) of the Chicago Approach frequency, transmitted from O’Hare Airport, Chicago, Illinois.
- Dallas Fort Worth Air Traffic Control Live ATC communications provided by CAE SimuFlite.
- K3FSS Pittsburgh Scanning Page RealAudio ATC sites.
- Low Approach.com A live feed of SoCal Approach where you can listen to aircraft entering Burbank (BUR) and Los Angeles International (LAX) airspace from the North/Northwest part of southern California.
- Live Air Traffic Control Links to live air traffic control (ATC) and airport web cams.
- LiveATC.Net Live aviation communications from all over the world brought to you by streaming audio technology. For aviation enthusiasts, student pilots, student air traffic controllers, flight simulation enthusiasts, FBO operators, airline operators, and anyone with an interest in aviation communications.
- Waterloo Live ATC This site broadcasts Air Traffic Control frequencies at the Region of Waterloo International Airport, located approximately 50 miles west of Toronto, and serving the cities of Kitchener, Waterloo, Cambridge, and Guelph in the province of Ontario, Canada.
- ZebthePilot.com Listen live to Boise, Idaho Air Traffic Control.
- Flight Dispatcher (Flight Operations Officer) Sites
- Airliner Dispatcher Resources A site for Aircraft Dispatchers or people seeking to get started in the aviation field.
- Flight Dispatch Services Ltd. A Polish flight dispatch center, with flight planning and support, and flight dispatcher training. Located in Warsaw.
- Flight Dispatchers Lots of information about flight dispatchers and aviation: overview of the profession, dispatchers in Turkey, airliners in Turkey, links, picture gallery.
- Flight Distatcher Organizations
- International Federation of Air Line Dispatchers’ Associations
- European Federation of Air Line Dispatchers Associations
- Airline Dispatchers Federation Organization for the airline dispatcher profession.
- Scandinavian Airline Dispatchers’ Association Denmark
- German Airline Dispatchers’ Association
- Icelandic Airline Dispatcher Association
- Polish Airline Dispatchers Association
- Swiss Airline Dispatchers’ Association
Air Traffic Management
- Airways New Zealand An air traffic management company that provides air navigation services to New Zealand, and is partnered with Lockheed Martin to provide air navigation services and products to other countries.
- Glossary of Air Traffic Management Terms An FAA table containing definitions and descriptions of many common Air Traffic Management acronyms.
- Thales Air Traffic Management Voice communication sytems for towers and centres.
Air Traffic Radar - A basic view
Air traffic radar enables split-second computations needed for decision making. The system helps controllers determine which instructions to send. Potentially dangerous air traffic situations can be diverted, hazardous weather systems noted, and relevant information transmitted to pilots and crew.
Today, much of the air to ground information is sent by computer links. This cuts down on the errors that come from mis-communication between air traffic controller and pilots.
The information from radar and flights shows up on electronic screens. This also allows the relay of greater amounts of data in less time. Air traffic control needs primary and secondary air traffic radar displays to keep track of the air planes and watch the weather. The secondary or beacon air traffic radar is usually attached to the same pole as the primary radar and they work in a synchronous fashion.
Radar information provides supporting knowledge necessary to prepare clearance information to relay to aircraft. Controllers then issue advisories and instructions to both IFR and VFR airplanes. The traffic advisories compiled by use of radar information may list altitudes, ranges and the bearings of aircraft located in close proximity to other flight paths.
Knowing and using this data helps avoid collisions by directing aircraft in order to maintain separation from other craft within their air space.
How the Information Gets Around
Every aircraft returns an echo of the primary signal after the primary radar sends out a high frequency signal burst. This allows the controller to know where each aircraft is located and then track its path.
Planes with transponders aboard can reply to the the beacon as well.
A special device queries the aircraft and receives vital information. A stream known as the Mode C signal pulse gets the current altitude of the plane. Mode A obtains its identity.
The transponder can automatically transmit a coded reply to the Mode C query. The Mode A query must be answered by a specific code with 4 assigned numbers manually entered by the pilot.
Radar helps air traffic controllers calculate ground speed, assess the current air traffic situation, such as monitoring for heavy air traffic and tracking each plane’s magnetic headings.
The radars automatically display electronically mapped and calculated flight plans for every plane. Radio signals can be used to calculate altitudes, speeds, directions, and locations of planes. This same radar technology delivers similar information on ships, cars, and storms.
The transmitter for the radar will send out short, high frequency radio pulse waves which bounce off of the target object. This frequency pulse lasts for a fraction of a second and the transmitter then closes while the receiver opens to receive the echo.
When signals get back to the receiver, the radar determines the length of time it took for the return signal. Some radar equipment calculates a Doppler shift in the echoed signals. Analyzing these measurements gives the location and the flying speed of the tracked aircraft.
To recap: the radar antenna sends out pulses of radio waves to the aircraft and it picks up the weaker returned signals. Even with weak radio waves or signals being returned, it is easy to process the information with the use of amplification as radio waves are easy signals to amplify.
Air traffic radar enables split-second computations needed for decision making. The system helps controllers determine which instructions to send. Potentially dangerous air traffic situations can be diverted, hazardous weather systems noted, and relevant information transmitted to pilots and crew.
Today, much of the air to ground information is sent by computer links. This cuts down on the errors that come from mis-communication between air traffic controller and pilots.
The information from radar and flights shows up on electronic screens. This also allows the relay of greater amounts of data in less time. Air traffic control needs primary and secondary air traffic radar displays to keep track of the air planes and watch the weather. The secondary or beacon air traffic radar is usually attached to the same pole as the primary radar and they work in a synchronous fashion.
Radar information provides supporting knowledge necessary to prepare clearance information to relay to aircraft. Controllers then issue advisories and instructions to both IFR and VFR airplanes. The traffic advisories compiled by use of radar information may list altitudes, ranges and the bearings of aircraft located in close proximity to other flight paths.
Knowing and using this data helps avoid collisions by directing aircraft in order to maintain separation from other craft within their air space.
How the Information Gets Around
Every aircraft returns an echo of the primary signal after the primary radar sends out a high frequency signal burst. This allows the controller to know where each aircraft is located and then track its path.
Planes with transponders aboard can reply to the the beacon as well.
A special device queries the aircraft and receives vital information. A stream known as the Mode C signal pulse gets the current altitude of the plane. Mode A obtains its identity.
The transponder can automatically transmit a coded reply to the Mode C query. The Mode A query must be answered by a specific code with 4 assigned numbers manually entered by the pilot.
Radar helps air traffic controllers calculate ground speed, assess the current air traffic situation, such as monitoring for heavy air traffic and tracking each plane’s magnetic headings.
The radars automatically display electronically mapped and calculated flight plans for every plane. Radio signals can be used to calculate altitudes, speeds, directions, and locations of planes. This same radar technology delivers similar information on ships, cars, and storms.
The transmitter for the radar will send out short, high frequency radio pulse waves which bounce off of the target object. This frequency pulse lasts for a fraction of a second and the transmitter then closes while the receiver opens to receive the echo.
When signals get back to the receiver, the radar determines the length of time it took for the return signal. Some radar equipment calculates a Doppler shift in the echoed signals. Analyzing these measurements gives the location and the flying speed of the tracked aircraft.
To recap: the radar antenna sends out pulses of radio waves to the aircraft and it picks up the weaker returned signals. Even with weak radio waves or signals being returned, it is easy to process the information with the use of amplification as radio waves are easy signals to amplify.
En route Air Traffic Controller Commands
The Federal Aviation Administration (FAA) is developing the En route Automation Modernization (ERAM) system to replace the legacy en route Air Traffic Control (ATC) automation system that consists of the Host Computer System (HCS), the Display System Replacement (DSR), and the User Request Evaluation Tool (URET). En route controllers use the legacy system to control thousands of flights each day at 20 Air Route Traffic Control Centers (ARTCCs) in the conterminous United States. Lockheed Martin Corporation is the primary ERAM contractor.
The Test and Evaluation Master Plan for ERAM requires that the ERAM Test Program verify critical operational issues (COIs) (FAA, 2003). The first COI requires that ERAM support en route ATC operations with at least the same effectiveness as the legacy system. Therefore, ERAM must allow controllers to accomplish their tasks as well or better than HCS, DSR, and URET. To determine this, the baseline performance of the legacy system must be measured to provide standards for later comparisons to ERAM.
Purpose
This technical note provides the frequency of use of controller commands using the legacy en route ATC system from one typical en route facility. This study is one of several conducted by the Automation Metrics Test Working Group (AMTWG) described in the ERAM Automation Metrics and Preliminary Test Implementation Plan (FAA, 2005).
Background
The FAA ERAM Test Group formed the AMTWG in 2004. The team supports ERAM developmental and operational testing by developing metrics that quantify the effectiveness of key system capabilities in ERAM. The targeted capabilities are the Surveillance Data Processing (SDP), Flight Data Processing (FDP), Conflict Probe Tool (CPT), and the Display System (DS) modules. The metrics are designed to measure the performance of the legacy system and to allow valid comparisons to ERAM.
The metrics development project will occur in several phases. First, during 2004, the AMTWG generated a list of approximately 100 metrics and mapped them to the services and capabilities found in the Blueprint for the National Airspace System Modernization 2002 Update (FAA, 2002). The initial metrics were published in a progress report (FAA, 2004b). Second, during 2005, the team prioritized the metrics for more refinement and created an implementation plan (FAA, 2005). The implementation plan lists the selected metrics, gives rationales for their selection, and describes how they identified high priority metrics. The implementation plan allows each metric to be traced to basic controller decisions and tasks, COIs, and the ERAM contractor’s technical performance measurements. The categories of high priority metrics are
• SDP radar tracking,
• SDP tactical alert processing,
• FDP flight plan route expansion,
• FDP aircraft trajectory generation,
• CPT strategic aircraft-to-aircraft conflict prediction,
• CPT aircraft-to-airspace conflict prediction,
• additional system level metrics, and
• DS human factors and performance metrics.
In the final project phase, the AMTWG will further refine and apply the metrics to the legacy en route automation system. The team is planning to deliver four reports for fiscal year 2005 with one covering each of the ERAM components discussed previously: SDP, FDP, CPT, and DS.
These reports will be published in several deliveries to the ERAM Test Group. This technical note documents the second of these reports examining the ERAM DS. It documents the frequency of use for current en route control automation commands and allows testers to target those aspects of ERAM that controllers use most. Later reports will provide equivalent measures for the operational criticality of commands and examine commands for detailed usage characteristics.
User Interface Changes in En route Automation Modernization ERAM provides a variety of new user interface (UI) capabilities over the legacy automation system. These include
The Test and Evaluation Master Plan for ERAM requires that the ERAM Test Program verify critical operational issues (COIs) (FAA, 2003). The first COI requires that ERAM support en route ATC operations with at least the same effectiveness as the legacy system. Therefore, ERAM must allow controllers to accomplish their tasks as well or better than HCS, DSR, and URET. To determine this, the baseline performance of the legacy system must be measured to provide standards for later comparisons to ERAM.
Purpose
This technical note provides the frequency of use of controller commands using the legacy en route ATC system from one typical en route facility. This study is one of several conducted by the Automation Metrics Test Working Group (AMTWG) described in the ERAM Automation Metrics and Preliminary Test Implementation Plan (FAA, 2005).
Background
The FAA ERAM Test Group formed the AMTWG in 2004. The team supports ERAM developmental and operational testing by developing metrics that quantify the effectiveness of key system capabilities in ERAM. The targeted capabilities are the Surveillance Data Processing (SDP), Flight Data Processing (FDP), Conflict Probe Tool (CPT), and the Display System (DS) modules. The metrics are designed to measure the performance of the legacy system and to allow valid comparisons to ERAM.
The metrics development project will occur in several phases. First, during 2004, the AMTWG generated a list of approximately 100 metrics and mapped them to the services and capabilities found in the Blueprint for the National Airspace System Modernization 2002 Update (FAA, 2002). The initial metrics were published in a progress report (FAA, 2004b). Second, during 2005, the team prioritized the metrics for more refinement and created an implementation plan (FAA, 2005). The implementation plan lists the selected metrics, gives rationales for their selection, and describes how they identified high priority metrics. The implementation plan allows each metric to be traced to basic controller decisions and tasks, COIs, and the ERAM contractor’s technical performance measurements. The categories of high priority metrics are
• SDP radar tracking,
• SDP tactical alert processing,
• FDP flight plan route expansion,
• FDP aircraft trajectory generation,
• CPT strategic aircraft-to-aircraft conflict prediction,
• CPT aircraft-to-airspace conflict prediction,
• additional system level metrics, and
• DS human factors and performance metrics.
In the final project phase, the AMTWG will further refine and apply the metrics to the legacy en route automation system. The team is planning to deliver four reports for fiscal year 2005 with one covering each of the ERAM components discussed previously: SDP, FDP, CPT, and DS.
These reports will be published in several deliveries to the ERAM Test Group. This technical note documents the second of these reports examining the ERAM DS. It documents the frequency of use for current en route control automation commands and allows testers to target those aspects of ERAM that controllers use most. Later reports will provide equivalent measures for the operational criticality of commands and examine commands for detailed usage characteristics.
User Interface Changes in En route Automation Modernization ERAM provides a variety of new user interface (UI) capabilities over the legacy automation system. These include
- toolbars and buttons that can be “torn off” of the main toolbars and placed in different locations,
- expansion of the capability to issue multiple commands to a track using a single entry,
- a capability to issue the same command to multiple tracks using a single entry,
- a capability to preprogram macros containing multiple commands and associate these macros with toolbar buttons,
- tabular lists that become interactive views where controllers can click on items, and
- flight plan readouts that automatically update instead of requiring the controller to manually update them.
Many of these new UI capabilities are intended to reduce routine data entry tasks by allowing controllers to accomplish several tasks at once. For example, for each aircraft arriving at a particular fix, a controller may need to enter a new interim altitude, hand the aircraft off to the next sector, and offset the datablock. A properly constructed macro would allow the controller to complete these three commands with a single entry.
An appropriate evaluation of these new capabilities would examine their effects on controller interactions. If the new capabilities are indeed beneficial to controllers, or at least do no harm, an equal number of or fewer interactions should be evident in ERAM. For example, if the tear- off toolbars are indeed beneficial, a reduction in time spent manipulating the overall toolbars might be evident. If data entry workload is reduced, controllers may be able to allocate the corresponding time and effort to other tasks such as planning, communicating, and separating aircraft. Accompanying increases in operational efficiency and possibly safety could result.
This report provides the frequency with which controllers make different entry types using the legacy automation system. These data can be used to guide future ERAM testing and to ensure that testing targets the most frequent and important controller commands.
Previous Research
During the development process for DSR, the National Airspace System (NAS) Human Factors Group conducted baseline simulations of the original HCS with the Plan View Display (PVD) (Galushka, Frederick, Mogford, & Krois, 1995) and the HCS with the DSR (Allendoerfer, Galushka, & Mogford, 2000). In these studies, we measured controller interactions and compared them at the level of HCS data entry types, such as None (QN) and Amendment (AM).
At the time, we did not examine the subtypes of HCS data entries. For example, the QN entry type contains Offset Datablock, Accept Handoff, and Assign Altitude commands. We did not evaluate these commands separately though they are conceptually very different.
We also did not consider the various ways that a data entry can be made. For example, an Assigned Altitude command can be entered by typing the desired altitude on the keyboard followed by the three-character Computer Identification (CID) for the aircraft. Assigned Altitude can also be entered by typing the altitude followed by the beacon code or callsign.
Finally, Assigned Altitude can be entered by typing the altitude on the keyboard and clicking on the aircraft with the trackball cursor. The multiple methods for entering an Assigned Altitude command differ in their information requirements, the amount of time and effort they require, and their appropriateness for a given situation.
In the earlier baseline studies, we did not measure the display control commands that are not processed by the HCS. These commands include adjusting the range, vector line length, and brightness. The primary reason for not including these commands was a lack of automated data collection capabilities on the PVD (these commands were provided with mechanical knobs at the time) and a lack of familiarity with the DSR data recording methods.
Finally, since we conducted our original studies, many changes have occurred in the legacy system. Most important, URET has been introduced and deployed to the field. It provides many new commands and changes the way that controllers accomplish original HCS commands like amending flight plans. In addition, new DSR capabilities have been introduced such as flyout menus that allow changes to altitude, speed, and heading and new toolbars that allow controllers to adjust range and add annotations.
The current project seeks to improve on all these limitations. We examine controller interactions at a much more detailed level than the earlier baselines, and we include all types of interactions, including display controls and URET commands. Finally, we use a much larger and richer data set that contains tens of thousands of interactions.
Functions and Interactions
Controller usage of a system can be analyzed at different levels of abstraction. At the highest level of abstraction, controllers’ overall goals can be examined, such as how successfully they maintain an efficient flow of traffic. It can be very difficult to formally evaluate complex systems at the goal level because so many other systems and factors, such as training and procedures, affect how well the system supports the achievement of the goals. In any case, the overall goals of the legacy system and ERAM do not change. Controllers are still expected to maintain a safe and efficient flow of traffic following the established procedures of the FAA and their local facility.
To achieve goals, a controller must engage in one or more tasks, such as maintaining an accurate flight database.
Evaluating a complex system at the task level is feasible, and the tasks that ERAM is intended to support are discussed in the implementation plan (FAA, 2005). In most cases, the tasks associated with the legacy system do not change in ERAM.
Accomplishing a task using the legacy system or ERAM requires that a controller use one or more system commands. A command is a system-oriented term relating to one thing the system can do, such as display a piece of information or accept a type of input data. Examples of commands include Assigned Altitude, Offset Datablock, and Amend Flight Plan. Analysis of the most commonly used commands is one focus of the current report.
In the legacy system and ERAM, many commands can be accomplished through one or more interaction methods. An interaction method is a group of individual actions that accomplish a command. For example, if a controller wishes to complete the Adjust Range command to change the zoom of his or her radar display, the controller can choose among the following interaction methods.
An appropriate evaluation of these new capabilities would examine their effects on controller interactions. If the new capabilities are indeed beneficial to controllers, or at least do no harm, an equal number of or fewer interactions should be evident in ERAM. For example, if the tear- off toolbars are indeed beneficial, a reduction in time spent manipulating the overall toolbars might be evident. If data entry workload is reduced, controllers may be able to allocate the corresponding time and effort to other tasks such as planning, communicating, and separating aircraft. Accompanying increases in operational efficiency and possibly safety could result.
This report provides the frequency with which controllers make different entry types using the legacy automation system. These data can be used to guide future ERAM testing and to ensure that testing targets the most frequent and important controller commands.
Previous Research
During the development process for DSR, the National Airspace System (NAS) Human Factors Group conducted baseline simulations of the original HCS with the Plan View Display (PVD) (Galushka, Frederick, Mogford, & Krois, 1995) and the HCS with the DSR (Allendoerfer, Galushka, & Mogford, 2000). In these studies, we measured controller interactions and compared them at the level of HCS data entry types, such as None (QN) and Amendment (AM).
At the time, we did not examine the subtypes of HCS data entries. For example, the QN entry type contains Offset Datablock, Accept Handoff, and Assign Altitude commands. We did not evaluate these commands separately though they are conceptually very different.
We also did not consider the various ways that a data entry can be made. For example, an Assigned Altitude command can be entered by typing the desired altitude on the keyboard followed by the three-character Computer Identification (CID) for the aircraft. Assigned Altitude can also be entered by typing the altitude followed by the beacon code or callsign.
Finally, Assigned Altitude can be entered by typing the altitude on the keyboard and clicking on the aircraft with the trackball cursor. The multiple methods for entering an Assigned Altitude command differ in their information requirements, the amount of time and effort they require, and their appropriateness for a given situation.
In the earlier baseline studies, we did not measure the display control commands that are not processed by the HCS. These commands include adjusting the range, vector line length, and brightness. The primary reason for not including these commands was a lack of automated data collection capabilities on the PVD (these commands were provided with mechanical knobs at the time) and a lack of familiarity with the DSR data recording methods.
Finally, since we conducted our original studies, many changes have occurred in the legacy system. Most important, URET has been introduced and deployed to the field. It provides many new commands and changes the way that controllers accomplish original HCS commands like amending flight plans. In addition, new DSR capabilities have been introduced such as flyout menus that allow changes to altitude, speed, and heading and new toolbars that allow controllers to adjust range and add annotations.
The current project seeks to improve on all these limitations. We examine controller interactions at a much more detailed level than the earlier baselines, and we include all types of interactions, including display controls and URET commands. Finally, we use a much larger and richer data set that contains tens of thousands of interactions.
Functions and Interactions
Controller usage of a system can be analyzed at different levels of abstraction. At the highest level of abstraction, controllers’ overall goals can be examined, such as how successfully they maintain an efficient flow of traffic. It can be very difficult to formally evaluate complex systems at the goal level because so many other systems and factors, such as training and procedures, affect how well the system supports the achievement of the goals. In any case, the overall goals of the legacy system and ERAM do not change. Controllers are still expected to maintain a safe and efficient flow of traffic following the established procedures of the FAA and their local facility.
To achieve goals, a controller must engage in one or more tasks, such as maintaining an accurate flight database.
Evaluating a complex system at the task level is feasible, and the tasks that ERAM is intended to support are discussed in the implementation plan (FAA, 2005). In most cases, the tasks associated with the legacy system do not change in ERAM.
Accomplishing a task using the legacy system or ERAM requires that a controller use one or more system commands. A command is a system-oriented term relating to one thing the system can do, such as display a piece of information or accept a type of input data. Examples of commands include Assigned Altitude, Offset Datablock, and Amend Flight Plan. Analysis of the most commonly used commands is one focus of the current report.
In the legacy system and ERAM, many commands can be accomplished through one or more interaction methods. An interaction method is a group of individual actions that accomplish a command. For example, if a controller wishes to complete the Adjust Range command to change the zoom of his or her radar display, the controller can choose among the following interaction methods.
- On the Situation Display (SD) Range Toolbar, click on the current range value and type the desired value with the keyboard.
- On the SD Range Toolbar, move the cursor over the “-/+” pick area. Click with the trackball pick or enter key to decrease or increase the value.
- On the SD Range Toolbar, click and drag the range slider bar to the desired value. Alternately, click the trough areas of the slider to decrease or increase the value.
- On the SD Range Toolbar, click on one of two preset range settings to change the current setting to the preset value.
- On the Keypad Selection Device (KSD), press one of the RNG range arrow keys (marked “RNG”) to increase or decrease the setting.
- Activate a preference set with a different range setting.
The second focus of the current report is to examine the specific interaction methods that controllers use to accomplish commands. An interaction method is made up of individual user actions. An action is a keystroke or a trackball button click. Some interaction methods require many actions, others require very few. In the current report, we do not analyze the data at the action level. That is, we are not concerned here with individual keystrokes or clicks. The data reduction methods described here, however, do allow for analysis at the action level if needed in the future.
Data Collection
To provide the most comprehensive data set possible, we based the analysis on System Analysis Recording (SAR) data recorded by the FAA Integration and Interoperability Facility (I2F) at Washington ARTCC (ZDC) on March 17-18, 2005. These recordings were made to assist the AMTWG in a number of its activities. The data set includes 11 hours 25 minutes of controller interactions recorded across the entire facility, including more than 110 operational positions and more than 50 sectors. This represents 663 controller shifts and 168 individual controllers. The dataset includes over 200,000 controller interactions and responses. To our knowledge, this is the largest in-depth analysis of en route controller interactions ever conducted by the FAA.
Data Reduction
Several steps were necessary to prepare the data for the analysis. Existing software tools did not provide the level of analysis required for this project. As a result, we used a combination of existing and custom-developed tools.
Database Fields
The primary levels of analysis in this report are commands and interaction methods.
HCS Data Reduction
We had experience working with HCS SAR tapes during earlier baseline studies, such as the DSR Baseline (Allendoerfer et al., 2000). However, no suitable tools existed for reducing or analyzing the tapes at the level of detail required for this project. Using Microsoft Excel and Visual Basic for Applications (VBA), we created a data reduction tool called Entry Counter.
Assumptions
The following section describes assumptions we made while conducting the data analysis of the HCS data.
Matching Entry and Response Messages
When a controller makes an incorrect HCS entry, the HCS provides a response message. In some cases, the HCS also provides response messages for accepted entries, as in flight plan readout entries. Unfortunately, there is no simple way to use the HCS data to match a response message to the entry that generated it, especially when the response is a general error message such as MESSAGE TOO SHORT.
Because we are interested in error rates for different commands, we have implemented a matching algorithm in Entry Counter. The algorithm appears to provide accurate matching of responses to the entries that generated them. To qualify as a match,
Data Collection
To provide the most comprehensive data set possible, we based the analysis on System Analysis Recording (SAR) data recorded by the FAA Integration and Interoperability Facility (I2F) at Washington ARTCC (ZDC) on March 17-18, 2005. These recordings were made to assist the AMTWG in a number of its activities. The data set includes 11 hours 25 minutes of controller interactions recorded across the entire facility, including more than 110 operational positions and more than 50 sectors. This represents 663 controller shifts and 168 individual controllers. The dataset includes over 200,000 controller interactions and responses. To our knowledge, this is the largest in-depth analysis of en route controller interactions ever conducted by the FAA.
Data Reduction
Several steps were necessary to prepare the data for the analysis. Existing software tools did not provide the level of analysis required for this project. As a result, we used a combination of existing and custom-developed tools.
Database Fields
The primary levels of analysis in this report are commands and interaction methods.
HCS Data Reduction
We had experience working with HCS SAR tapes during earlier baseline studies, such as the DSR Baseline (Allendoerfer et al., 2000). However, no suitable tools existed for reducing or analyzing the tapes at the level of detail required for this project. Using Microsoft Excel and Visual Basic for Applications (VBA), we created a data reduction tool called Entry Counter.
Assumptions
The following section describes assumptions we made while conducting the data analysis of the HCS data.
Matching Entry and Response Messages
When a controller makes an incorrect HCS entry, the HCS provides a response message. In some cases, the HCS also provides response messages for accepted entries, as in flight plan readout entries. Unfortunately, there is no simple way to use the HCS data to match a response message to the entry that generated it, especially when the response is a general error message such as MESSAGE TOO SHORT.
Because we are interested in error rates for different commands, we have implemented a matching algorithm in Entry Counter. The algorithm appears to provide accurate matching of responses to the entries that generated them. To qualify as a match,
- the response must be listed later in the data file than the entry,
- the response and entry must have occurred in the same sector and position,
- the response and entry must occur within 2.5 seconds of each other, and
- the entry cannot already have a response assigned to it.
Issues
The following subsections describe issues we encountered while reducing and analyzing the HCS SAR data. In future projects, fixes or workarounds for these problems may be necessary.
Implied Aircraft Selections: Implied entries are HCS entries where the controller does not press a command key at the beginning of the entry. In these cases, the HCS determines the meaning of the entry from other data in the entry and, in some cases, the context in which the entry occurs. For example, clicking on a track with no accompanying data in the Message Composition area or entering a CID with no accompanying data (e.g., 56E <enter>) yields different outcomes depending on the status of the track. If the aircraft is in handoff status, the HCS interprets the entry as Accept Handoff. If the aircraft is not in handoff status and being shown as a limited datablock, the HCS interprets the entry as Force Datablock (i.e., the datablock is displayed as a full even though the controller does not own the target).
The HCS SAR recordings do not contain a simple manner to determine the context of implied aircraft selections. They list that the controller clicked on a target and that no error was generated. However, the recordings do not indicate directly whether the click resulted in an Accept Handoff or Force Datablock command. To determine this, a much more detailed analysis of the track data would be necessary. The level of ambiguity in this algorithm is not desirable.
These are reported as “Implied Aircraft Selection” as a separate entry type even though it is truly composed of Accept Handoff and Force Datablock. Future analyses should explore mechanisms for determining the status of aircraft to establish the context and nature of implied aircraft selections.
Unreliable Timestamps
A response message occurs after the entry that generated it. However, in the HCS data, the timestamps for response messages sometimes showed that the response occurred at the same time or occasionally several milliseconds before the entry that generated it. We suspect this issue is caused by the recording priorities and techniques of the HCS. To account for these discrepancies, calculations in Entry Counter involving time are programmed to consider a window of time rather than a value in a specific direction. For example, Entry Counter requires a response message to occur within 2.5 seconds of an originating entry to qualify as a match rather than requiring the response to occur after the entry.
The sequence of lines in the HCS data appears to reliably reflect the order of events. That is, a response message is always listed after its originating entry regardless of their timestamps. This allows Entry Counter to consider the line number in addition to timestamps in some of its calculations. For example, in addition to requiring a window of time, Entry Counter requires that a response message occur later in the data file than the entry to qualify as a match.
Undetermined Frequent Blank Entries
The HCS data included a number of blank entries that had no obvious equivalents in the DSR or URET data. These entries appear as if the controller pressed the Enter key with no data in the Message Composition area. Typically, blank entries receive a MESSAGE TOO SHORT response. We have seen controllers habitually press the Clear key, but we currently have no explanation for why they would press the Enter key so frequently with no data in the composition area. The frequency of these entries leads us to suspect that they result from interactions with DSR or URET that we do not currently understand. We suspect that if controllers were actually seeing so many MESSAGE TOO SHORT response messages, they would have complained. These are reported as “Undetermined” in subsequent analyses.
Unmatched Responses
The HCS SAR includes responses to all types of entries, even if those commands were entered through a mechanism other than the HCS. This leads to response messages that seemingly do not have an originating entry. For example, if a controller enters a flight plan amendment through URET, the HCS still processes the amendment and provides a response. There is no record in the HCS SAR of the entry itself because it was made through URET. However, the response message does appear in the controller’s readout area and is recorded in the HCS SAR data. This leads to “orphaned” response messages that can only be resolved by manually considering the DSR and URET data in parallel, which is beyond the scope of this analysis.
No Quicklook Entries
For reasons we have not been able to identify, no Quicklook (QL) commands appear in the HCS SAR data. We see no reason why these commands should not appear when all other HCS commands do, including many obscure ones. QL commands do appear in the corresponding DSR files, and we have used these in the counts reported in this document.
DSR and URET Data Reduction
Unlike the HCS data, we had no previous experience working with DSR SAR files, which contain data about controller interactions made through DSR and URET. An additional level of reduction was necessary for these data. First, we used the System Wide Analysis Capability (SWAC) tool to pull gates (i.e., units of recording) that apply to controller interactions.
Edges of Interactions
Many entries in DSR involve rapid repetition of the same action. For example, to increase the vector line length, a controller may click on the VECTOR pick area in the with the center trackball button. One click increases the vector line length by one available value (i.e., 0, 1, 2, 4, or 8 minutes of flying time). If the controller wishes to increase the length by multiple units, multiple clicks are necessary.
In our analysis, we treat rapid repetition of the same DSR action by the same controller as multiple clicks serving to create a single entry. This is to ensure comparability with the HCS entries in which many keystrokes are necessary to compose a single entry. To determine what qualifies as rapid repetition, we examined DSR entries of various types and determined that a window of 1 second provided reasonable, interpretable sequences. For example, the controller makes eight keystrokes in a row on the KSD. The first four keystrokes, each occurring within 1 second of its predecessor, all were on the VECT key. The second four keystrokes, each occurring with 1 second of its predecessor, all were on the VECT key. The gap of about 10 seconds between the fourth and fifth keystroke and that the controller pressed different keys forms the break between one Adjust Vector Line entry and another.
Preference Set Clusters
Similar to rapid repetition, the application of a preference set in DSR results in a rapid sequence of display setting adjustments. Because these were generated by the preference set and not individual controller actions, they should be counted as part of the preference set, not separately. However, the DSR gates do not indicate whether a display setting adjustment was accomplished through a preference set. In our analysis, to count as a display setting adjustment resulting from a preference set, an adjustment must occur within 250 ms following a Sign In, Invoke Preference Set entry or within 250 ms following a display setting adjustment from a preference set. For example, in Figure 3, a controller signs in and immediately 15 changes are made to the display by the controller’s preference set. Two seconds later, the controller adjusts the range manually and makes another entry, which are separate from the preference set actions.
Issues
In the reduction and analysis of the DSR SAR files, we encountered several problems. The following sections discuss these problems and the methods we used to address or work around them.
Flyout Menus Not Recorded
AG_12026, the gate associated with the DSR flyout menus, was mistakenly not recorded in the data set from ZDC. This prevented us from examining controllers’ use of these menus in detail. However, because these are an important capability of DSR and have many analogs in new ERAM capabilities, we concluded that it was worthwhile to identify these commands as best we could from the AG_11806 gate, which records each trackball click and the views it affects.
In this way, even though we could not identify which pieces of the flyout menus were being clicked, we could at least determine the number of times controllers used the flyout menus. In addition, we adopted a criterion by which if the HCS received a Interim Altitude (QQ), Assigned Altitude (QZ), or Speed/Heading/Free Form Text (QS) entry that immediately followed clicks in a flyout menu (i.e., no other commands issued in between), the entry was counted as having been entered through the flyout menu. For example, a controller makes two picks in a flyout menu immediately followed by a change speed command. By our criteria, this entry was counted as having been made through the flyout menu and not by the keyboard.
Unmatched Responses
Like the HCS data, there are some response messages recorded in the DSR data that seem to have no originating event. The orphaned response messages typically are recorded as MESSAGE TOO SHORT. They are typically associated with blank HCS entries and do not appear in the DSR SAR. As a result, there are many MESSAGE TOO SHORT orphaned responses in the DSR data that cannot be tracked to an entry that generated them. By examining the HCS and DSR data in parallel, the orphaned messages can be resolved, though why so many blank HCS entries appear in the data set is not currently known.
Unidentified Commands
In the URET data, a message called DISPLAY_LOCATION occurred very frequently, often associated with other commands occurring within a few milliseconds. We believe that this message relates to updating the URET windows and lists, but we have not been able to identify its full purpose. Based on the frequency of the message, we believe that it is not a controller entry but rather a system message.
Filesize Issues
DSR SAR files contain enormous amounts of information, approximately 650 MB per hour in binary form. Reducing the data using SWAC for the selected gates produced files of approximately 50 MB per 40 minutes. The number of lines and entries tests the limits of Entry Counter in the Microsoft Excel VBA environment, which was selected for its simplicity and rapid development time. Future analyses of these data may require a more robust data reduction and database management system.
Results
The following sections contain tables showing the frequency of use of various controller commands. Later sections provide examples of detailed analysis of specific commands.
Details on Host Computer System Entries
The frequency of use data can be examined at many levels of detail using the other data fields. The syntax for these entries requires the controller to specify a flight identifier (FLID) in addition to other parameters.
The controller can do this using the beacon code (e.g., 32 6271 <enter>, which initiates a handoff of the aircraft with beacon code 6271 to Sector 32), the callsign (e.g., 50 USA176 <enter>), the CID (e.g., 38 88G <enter>), or by clicking on the target with the trackball (e.g., 12 <trackball>).
This type of analysis may be useful in ERAM testing because changes to the UI may affect which FLID method controllers select. For example, using the CID, a three-digit code (e.g., 128) is the most common FLID method for these entry types. Beacon code is four octal digits (e.g., 2477) and callsign can range from one to seven alphanumeric characters (e.g., AAL1234).
However, if the length of the CID is increased in ERAM from three to four characters, controllers may shift their preference toward the other methods. Because entry methods differ with respect to the amount of time or effort required, such a shift may result in changes in data entry workload.
Another type of analysis that may be useful in ERAM testing is to examine the mistakes controllers make for certain important commands.
For example, Initiate Handoff is an extremely common command on which controllers frequently make mistakes. In the ZDC data, controllers received an error nearly 9% of the time they attempted to initiate a handoff. This error rate creates workload and frustration for the controllers and increases the chances that erroneous data contains sample data for each of the ways that controllers can adjust the vector line length.
Similar to adjusting range, controllers choose to adjust the vector line using the KSD by a wide margin over the DC View. This type of analysis may be useful for ERAM testing because ERAM may provide new toolbar capabilities and methods for entering commands, similar to the SD Range Toolbar.
Discussion and Next Steps
Frequency Analysis
The main data table show which commands are used most frequently and the detailed analyses show how some common commands are used. For future ERAM testing, we recommend focusing on the top 30 commands because these will encompass about 95% of controller entries. Detailed analyses, such as those reported here, should be conducted for each selected entry type.
Critical Situation Analysis
Frequency of use is not the only factor affecting the operational significance of a command. Some commands are operationally important but used infrequently, especially those related to emergencies and other critical events. Because the analysis reported here is based on routine operations at ZDC, the frequency of use for rare but important commands may be underrepresented in Table 3. Additional analysis is required to identify commands that are operationally important in certain uncommon situations but infrequent during regular operations. We will conduct this analysis in 2005 by interviewing and surveying subject matter experts from ARTCCs. We will identify uncommon situations, such as emergencies and equipment outages, and identify the HCS/DSR/URET commands controllers use to respond. These commands may appear only rarely (or not at all) during the day-in-the-life analysis. These rare but important commands will be added to the list of commands for detailed analysis in later phases of the project.
Mapping of ERAM Changes
ERAM makes a number of changes to the legacy system. Some of these changes are directly related to the controller UI and have a clear potential to affect how controllers use the system. These effects can be beneficial or detrimental and will be examined in later phases of the ERAM testing.
However, other ERAM changes are not specifically targeted at the UI but may have latent effects on how controllers use the system. In later phases of the project, we will conduct an analysis to identify areas where other changes in ERAM may affect how controllers use and interact with the system. We will include these areas in our subsequent test plans and activities. There are other ERAM changes that we anticipate may have some effect on controllers:
The following subsections describe issues we encountered while reducing and analyzing the HCS SAR data. In future projects, fixes or workarounds for these problems may be necessary.
Implied Aircraft Selections: Implied entries are HCS entries where the controller does not press a command key at the beginning of the entry. In these cases, the HCS determines the meaning of the entry from other data in the entry and, in some cases, the context in which the entry occurs. For example, clicking on a track with no accompanying data in the Message Composition area or entering a CID with no accompanying data (e.g., 56E <enter>) yields different outcomes depending on the status of the track. If the aircraft is in handoff status, the HCS interprets the entry as Accept Handoff. If the aircraft is not in handoff status and being shown as a limited datablock, the HCS interprets the entry as Force Datablock (i.e., the datablock is displayed as a full even though the controller does not own the target).
The HCS SAR recordings do not contain a simple manner to determine the context of implied aircraft selections. They list that the controller clicked on a target and that no error was generated. However, the recordings do not indicate directly whether the click resulted in an Accept Handoff or Force Datablock command. To determine this, a much more detailed analysis of the track data would be necessary. The level of ambiguity in this algorithm is not desirable.
These are reported as “Implied Aircraft Selection” as a separate entry type even though it is truly composed of Accept Handoff and Force Datablock. Future analyses should explore mechanisms for determining the status of aircraft to establish the context and nature of implied aircraft selections.
Unreliable Timestamps
A response message occurs after the entry that generated it. However, in the HCS data, the timestamps for response messages sometimes showed that the response occurred at the same time or occasionally several milliseconds before the entry that generated it. We suspect this issue is caused by the recording priorities and techniques of the HCS. To account for these discrepancies, calculations in Entry Counter involving time are programmed to consider a window of time rather than a value in a specific direction. For example, Entry Counter requires a response message to occur within 2.5 seconds of an originating entry to qualify as a match rather than requiring the response to occur after the entry.
The sequence of lines in the HCS data appears to reliably reflect the order of events. That is, a response message is always listed after its originating entry regardless of their timestamps. This allows Entry Counter to consider the line number in addition to timestamps in some of its calculations. For example, in addition to requiring a window of time, Entry Counter requires that a response message occur later in the data file than the entry to qualify as a match.
Undetermined Frequent Blank Entries
The HCS data included a number of blank entries that had no obvious equivalents in the DSR or URET data. These entries appear as if the controller pressed the Enter key with no data in the Message Composition area. Typically, blank entries receive a MESSAGE TOO SHORT response. We have seen controllers habitually press the Clear key, but we currently have no explanation for why they would press the Enter key so frequently with no data in the composition area. The frequency of these entries leads us to suspect that they result from interactions with DSR or URET that we do not currently understand. We suspect that if controllers were actually seeing so many MESSAGE TOO SHORT response messages, they would have complained. These are reported as “Undetermined” in subsequent analyses.
Unmatched Responses
The HCS SAR includes responses to all types of entries, even if those commands were entered through a mechanism other than the HCS. This leads to response messages that seemingly do not have an originating entry. For example, if a controller enters a flight plan amendment through URET, the HCS still processes the amendment and provides a response. There is no record in the HCS SAR of the entry itself because it was made through URET. However, the response message does appear in the controller’s readout area and is recorded in the HCS SAR data. This leads to “orphaned” response messages that can only be resolved by manually considering the DSR and URET data in parallel, which is beyond the scope of this analysis.
No Quicklook Entries
For reasons we have not been able to identify, no Quicklook (QL) commands appear in the HCS SAR data. We see no reason why these commands should not appear when all other HCS commands do, including many obscure ones. QL commands do appear in the corresponding DSR files, and we have used these in the counts reported in this document.
DSR and URET Data Reduction
Unlike the HCS data, we had no previous experience working with DSR SAR files, which contain data about controller interactions made through DSR and URET. An additional level of reduction was necessary for these data. First, we used the System Wide Analysis Capability (SWAC) tool to pull gates (i.e., units of recording) that apply to controller interactions.
Edges of Interactions
Many entries in DSR involve rapid repetition of the same action. For example, to increase the vector line length, a controller may click on the VECTOR pick area in the with the center trackball button. One click increases the vector line length by one available value (i.e., 0, 1, 2, 4, or 8 minutes of flying time). If the controller wishes to increase the length by multiple units, multiple clicks are necessary.
In our analysis, we treat rapid repetition of the same DSR action by the same controller as multiple clicks serving to create a single entry. This is to ensure comparability with the HCS entries in which many keystrokes are necessary to compose a single entry. To determine what qualifies as rapid repetition, we examined DSR entries of various types and determined that a window of 1 second provided reasonable, interpretable sequences. For example, the controller makes eight keystrokes in a row on the KSD. The first four keystrokes, each occurring within 1 second of its predecessor, all were on the VECT key. The second four keystrokes, each occurring with 1 second of its predecessor, all were on the VECT key. The gap of about 10 seconds between the fourth and fifth keystroke and that the controller pressed different keys forms the break between one Adjust Vector Line entry and another.
Preference Set Clusters
Similar to rapid repetition, the application of a preference set in DSR results in a rapid sequence of display setting adjustments. Because these were generated by the preference set and not individual controller actions, they should be counted as part of the preference set, not separately. However, the DSR gates do not indicate whether a display setting adjustment was accomplished through a preference set. In our analysis, to count as a display setting adjustment resulting from a preference set, an adjustment must occur within 250 ms following a Sign In, Invoke Preference Set entry or within 250 ms following a display setting adjustment from a preference set. For example, in Figure 3, a controller signs in and immediately 15 changes are made to the display by the controller’s preference set. Two seconds later, the controller adjusts the range manually and makes another entry, which are separate from the preference set actions.
Issues
In the reduction and analysis of the DSR SAR files, we encountered several problems. The following sections discuss these problems and the methods we used to address or work around them.
Flyout Menus Not Recorded
AG_12026, the gate associated with the DSR flyout menus, was mistakenly not recorded in the data set from ZDC. This prevented us from examining controllers’ use of these menus in detail. However, because these are an important capability of DSR and have many analogs in new ERAM capabilities, we concluded that it was worthwhile to identify these commands as best we could from the AG_11806 gate, which records each trackball click and the views it affects.
In this way, even though we could not identify which pieces of the flyout menus were being clicked, we could at least determine the number of times controllers used the flyout menus. In addition, we adopted a criterion by which if the HCS received a Interim Altitude (QQ), Assigned Altitude (QZ), or Speed/Heading/Free Form Text (QS) entry that immediately followed clicks in a flyout menu (i.e., no other commands issued in between), the entry was counted as having been entered through the flyout menu. For example, a controller makes two picks in a flyout menu immediately followed by a change speed command. By our criteria, this entry was counted as having been made through the flyout menu and not by the keyboard.
Unmatched Responses
Like the HCS data, there are some response messages recorded in the DSR data that seem to have no originating event. The orphaned response messages typically are recorded as MESSAGE TOO SHORT. They are typically associated with blank HCS entries and do not appear in the DSR SAR. As a result, there are many MESSAGE TOO SHORT orphaned responses in the DSR data that cannot be tracked to an entry that generated them. By examining the HCS and DSR data in parallel, the orphaned messages can be resolved, though why so many blank HCS entries appear in the data set is not currently known.
Unidentified Commands
In the URET data, a message called DISPLAY_LOCATION occurred very frequently, often associated with other commands occurring within a few milliseconds. We believe that this message relates to updating the URET windows and lists, but we have not been able to identify its full purpose. Based on the frequency of the message, we believe that it is not a controller entry but rather a system message.
Filesize Issues
DSR SAR files contain enormous amounts of information, approximately 650 MB per hour in binary form. Reducing the data using SWAC for the selected gates produced files of approximately 50 MB per 40 minutes. The number of lines and entries tests the limits of Entry Counter in the Microsoft Excel VBA environment, which was selected for its simplicity and rapid development time. Future analyses of these data may require a more robust data reduction and database management system.
Results
The following sections contain tables showing the frequency of use of various controller commands. Later sections provide examples of detailed analysis of specific commands.
Details on Host Computer System Entries
The frequency of use data can be examined at many levels of detail using the other data fields. The syntax for these entries requires the controller to specify a flight identifier (FLID) in addition to other parameters.
The controller can do this using the beacon code (e.g., 32 6271 <enter>, which initiates a handoff of the aircraft with beacon code 6271 to Sector 32), the callsign (e.g., 50 USA176 <enter>), the CID (e.g., 38 88G <enter>), or by clicking on the target with the trackball (e.g., 12 <trackball>).
This type of analysis may be useful in ERAM testing because changes to the UI may affect which FLID method controllers select. For example, using the CID, a three-digit code (e.g., 128) is the most common FLID method for these entry types. Beacon code is four octal digits (e.g., 2477) and callsign can range from one to seven alphanumeric characters (e.g., AAL1234).
However, if the length of the CID is increased in ERAM from three to four characters, controllers may shift their preference toward the other methods. Because entry methods differ with respect to the amount of time or effort required, such a shift may result in changes in data entry workload.
Another type of analysis that may be useful in ERAM testing is to examine the mistakes controllers make for certain important commands.
For example, Initiate Handoff is an extremely common command on which controllers frequently make mistakes. In the ZDC data, controllers received an error nearly 9% of the time they attempted to initiate a handoff. This error rate creates workload and frustration for the controllers and increases the chances that erroneous data contains sample data for each of the ways that controllers can adjust the vector line length.
Similar to adjusting range, controllers choose to adjust the vector line using the KSD by a wide margin over the DC View. This type of analysis may be useful for ERAM testing because ERAM may provide new toolbar capabilities and methods for entering commands, similar to the SD Range Toolbar.
Discussion and Next Steps
Frequency Analysis
The main data table show which commands are used most frequently and the detailed analyses show how some common commands are used. For future ERAM testing, we recommend focusing on the top 30 commands because these will encompass about 95% of controller entries. Detailed analyses, such as those reported here, should be conducted for each selected entry type.
Critical Situation Analysis
Frequency of use is not the only factor affecting the operational significance of a command. Some commands are operationally important but used infrequently, especially those related to emergencies and other critical events. Because the analysis reported here is based on routine operations at ZDC, the frequency of use for rare but important commands may be underrepresented in Table 3. Additional analysis is required to identify commands that are operationally important in certain uncommon situations but infrequent during regular operations. We will conduct this analysis in 2005 by interviewing and surveying subject matter experts from ARTCCs. We will identify uncommon situations, such as emergencies and equipment outages, and identify the HCS/DSR/URET commands controllers use to respond. These commands may appear only rarely (or not at all) during the day-in-the-life analysis. These rare but important commands will be added to the list of commands for detailed analysis in later phases of the project.
Mapping of ERAM Changes
ERAM makes a number of changes to the legacy system. Some of these changes are directly related to the controller UI and have a clear potential to affect how controllers use the system. These effects can be beneficial or detrimental and will be examined in later phases of the ERAM testing.
However, other ERAM changes are not specifically targeted at the UI but may have latent effects on how controllers use the system. In later phases of the project, we will conduct an analysis to identify areas where other changes in ERAM may affect how controllers use and interact with the system. We will include these areas in our subsequent test plans and activities. There are other ERAM changes that we anticipate may have some effect on controllers:
- ERAM will use a single flight database across multiple ARTCCs. This may require modification to the number of characters in the CID to accommodate a larger number of simultaneous tracks. Given the number of times controllers enter the CID (over 7000 times per hour across the ZDC dataset), this change could have a substantial effect on how controllers make entries and use ERAM.
- ERAM will incorporate new tracker algorithms. Other members of the AMTWG are examining the ERAM tracker from the accuracy and performance standpoints. However, as occurred on the Standard Terminal Automation Replacement System (STARS) deployment, changes in tracker algorithms, if obvious to controllers, can affect controllers’ acceptance of and trust in the new system. Identification of situations where controllers might notice differences in ERAM due to its tracker algorithm should be identified early and included in ERAM testing and training.
- ERAM will contain a new approach toward system redundancy and backup. This change is not targeted at the UI but may affect how controllers respond to equipment outages.
Usage Characteristics
Once a suitable list of frequent and critical commands has been compiled, we may conduct detailed analyses to determine usage characteristics for each. Usage characteristics include some of the sample analyses reported here but also examine each command at a very detailed level.
The usage characteristics assessment for each command will include the following details:
Once a suitable list of frequent and critical commands has been compiled, we may conduct detailed analyses to determine usage characteristics for each. Usage characteristics include some of the sample analyses reported here but also examine each command at a very detailed level.
The usage characteristics assessment for each command will include the following details:
- Proportion of Data Entry Method (keyboard, trackball, flyout menu, URET, etc.);
- Time to complete the command;
- Number of keystrokes or mouse clicks required;
- Error rate and common categories of data entry errors for the command and
- Time spent looking at the keyboard, trackball, keypad, or screen while entering the command.
We will base the usage characteristic assessment on data already collected from ZDC and other ARTCCs. The analysis will also include observations and measurements made in the I F for critical commands that are not found in the day-in-the-life recordings.
Additional Facilities
All the analyses reported here are based on data recorded at ZDC. Though these data represent the largest analysis of this type ever attempted, ZDC is not representative of all ARTCCs in terms of its traffic, procedures, equipment, or work practices. In particular, other ARTCCs have received significant new equipment such as Traffic Management Advisor (TMA). A more definitive analysis of usage of the legacy system should account for some observed interfacility differences.
Data for seven adjacent ARTCCs were collected at the same time as the ZDC data and could be used for validation or to further generalize the results reported here. Examination of ARTCCs where TMA or other tools have been deployed may be informative regarding the effects on controller interactions. Possible explanations of observed interfacility differences could be differences in traffic pattern, traffic volume, unusual events such as emergencies or equipment outages, airspace size and design, and local procedures and practices.
Baseline Simulation Test Plan
The best method for directly comparing controller usage of the legacy system and ERAM is to conduct a baseline simulation on both platforms. In the baseline simulations, controllers will be presented with selected traffic situations and asked to respond. Controllers will respond to the same situations using both systems. The same metrics will be calculated for both systems and direct comparisons can be made with a minimum of confounding variables. Discussion of the baseline methodology can be found in the Air Traffic Control Baseline Methodology Guide (Allendoerfer & Galushka, 1999) and the reports of baseline simulations conducted for the PVD (Galushka et al., 1995) and the DSR (Allendoerfer, Galushka, & Mogford, 2000).
If the changes in ERAM result in changes in how controllers interact with the system, these differences should appear in the baseline metrics. For example, if the ERAM macro capability is beneficial to controllers’ data entry workload, the benefits should appear as reductions in the number of entries, error rate, or time to complete. Alternately, the ERAM capabilities could shift controllers’ preferred method for completing certain entries from the keyboard to the trackball, which would appear as differences in interaction method. If changes in ERAM result in changes in other aspects of controllers’ tasks, such as operational efficiency, these differences should appear in other baseline metrics. These metrics include measures of air traffic safety, efficiency, and workload.
For example, if an ERAM change reduces controller data entry workload which, in turn, results in controllers being able to handle more traffic, baseline metrics such as the number of aircraft handled per hour or the average time in the airspace may show improvements. In preparation for the baseline simulations, we could write a test plan that outlines the situations to be simulated, metrics that will be captured, and other methodological details. The descriptions of the simulated situations will outline requirements for traffic volume and characteristics (e.g., number of aircraft, number of intersecting trajectories) and events (e.g., emergencies, outages) that will occur in several scenarios. The simulated situations will allow controllers to exercise all selected commands and will be designed to elicit latent effects of other ERAM changes, if any. We will develop and shakedown the scenarios as part of preparations for the simulations.
Additional Facilities
All the analyses reported here are based on data recorded at ZDC. Though these data represent the largest analysis of this type ever attempted, ZDC is not representative of all ARTCCs in terms of its traffic, procedures, equipment, or work practices. In particular, other ARTCCs have received significant new equipment such as Traffic Management Advisor (TMA). A more definitive analysis of usage of the legacy system should account for some observed interfacility differences.
Data for seven adjacent ARTCCs were collected at the same time as the ZDC data and could be used for validation or to further generalize the results reported here. Examination of ARTCCs where TMA or other tools have been deployed may be informative regarding the effects on controller interactions. Possible explanations of observed interfacility differences could be differences in traffic pattern, traffic volume, unusual events such as emergencies or equipment outages, airspace size and design, and local procedures and practices.
Baseline Simulation Test Plan
The best method for directly comparing controller usage of the legacy system and ERAM is to conduct a baseline simulation on both platforms. In the baseline simulations, controllers will be presented with selected traffic situations and asked to respond. Controllers will respond to the same situations using both systems. The same metrics will be calculated for both systems and direct comparisons can be made with a minimum of confounding variables. Discussion of the baseline methodology can be found in the Air Traffic Control Baseline Methodology Guide (Allendoerfer & Galushka, 1999) and the reports of baseline simulations conducted for the PVD (Galushka et al., 1995) and the DSR (Allendoerfer, Galushka, & Mogford, 2000).
If the changes in ERAM result in changes in how controllers interact with the system, these differences should appear in the baseline metrics. For example, if the ERAM macro capability is beneficial to controllers’ data entry workload, the benefits should appear as reductions in the number of entries, error rate, or time to complete. Alternately, the ERAM capabilities could shift controllers’ preferred method for completing certain entries from the keyboard to the trackball, which would appear as differences in interaction method. If changes in ERAM result in changes in other aspects of controllers’ tasks, such as operational efficiency, these differences should appear in other baseline metrics. These metrics include measures of air traffic safety, efficiency, and workload.
For example, if an ERAM change reduces controller data entry workload which, in turn, results in controllers being able to handle more traffic, baseline metrics such as the number of aircraft handled per hour or the average time in the airspace may show improvements. In preparation for the baseline simulations, we could write a test plan that outlines the situations to be simulated, metrics that will be captured, and other methodological details. The descriptions of the simulated situations will outline requirements for traffic volume and characteristics (e.g., number of aircraft, number of intersecting trajectories) and events (e.g., emergencies, outages) that will occur in several scenarios. The simulated situations will allow controllers to exercise all selected commands and will be designed to elicit latent effects of other ERAM changes, if any. We will develop and shakedown the scenarios as part of preparations for the simulations.
General Control
ATC SERVICE
The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic, and to provide support for National Security and Homeland Defense. In addition to its primary function, the ATC system has the capability to provide (with certain limitations) additional services. The ability to provide additional services is limited by many factors, such as the volume of traffic, frequency congestion, quality of radar, controller workload, higher priority duties, and the pure physical inability to scan and detect those situations that fall in this category. It is recognized that these services cannot be provided in cases in which the provision of services is precluded by the above factors. Consistent with the aforementioned conditions, controllers shall provide additional service procedures to the extent permitted by higher priority duties and other circumstances. The provision of additional services is not optional on the part of the controller, but rather is required when the work situation permits. Provide air traffic control service in accordance with the procedures and minima in this order except when:
The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic, and to provide support for National Security and Homeland Defense. In addition to its primary function, the ATC system has the capability to provide (with certain limitations) additional services. The ability to provide additional services is limited by many factors, such as the volume of traffic, frequency congestion, quality of radar, controller workload, higher priority duties, and the pure physical inability to scan and detect those situations that fall in this category. It is recognized that these services cannot be provided in cases in which the provision of services is precluded by the above factors. Consistent with the aforementioned conditions, controllers shall provide additional service procedures to the extent permitted by higher priority duties and other circumstances. The provision of additional services is not optional on the part of the controller, but rather is required when the work situation permits. Provide air traffic control service in accordance with the procedures and minima in this order except when:
- A deviation is necessary to conform with ICAO Documents, National Rules of the Air, or special agreements where the U.S. provides air traffic control service in airspace outside the U.S. and its possessions or:
- NOTE- Pilots are required to abide by CFRs or other applicable regulations regardless of the application of any procedure or minima in this order.
- Other procedures/minima are prescribed in a letter of agreement, FAA directive, or a military document, or:
- NOTE- These procedures may include altitude reservations, air refueling, fighter interceptor operations, law enforcement, etc.
- A deviation is necessary to assist an aircraft when an emergency has been declared.
DUTY PRIORITY
- Give first priority to separating aircraft and issuing safety alerts as required in this order. Good judgment shall be used in prioritizing all other provisions of this order based on the requirements of the situation at hand.
- NOTE- Because there are many variables involved, it is virtually impossible to develop a standard list of duty priorities that would apply uniformly to every conceivable situation. Each set of circumstances must be evaluated on its own merit, and when more than one action is required, controllers shall exercise their best judgment based on the facts and circumstances known to them. That action which is most critical from a safety standpoint is performed first.
- Provide support to national security and homeland defense activities to include, but
- Provide additional services to the extent possible, contingent only upon higher priority duties and other factors including limitations of radar, volume of traffic, frequency congestion, and workload.
- Use automation procedures in preference to nonautomation procedures when workload, communications, and equipment capabilities permit.
- Use radar separation in preference to nonradar separation when it will be to an operational advantage and workload, communications, and equipment permit.
- Use nonradar separation in preference to radar separation when the situation dictates that an operational advantage will be gained.
- NOTE- One situation may be where vertical separation would preclude excessive vectoring.
OPERATIONAL PRIORITY
Provide air traffic control service to aircraft on a “first come, first served” basis as circumstances permit, except the following:
NOTE- It is solely the pilot’s prerogative to cancel an IFR flight plan. However, a pilot’s retention of an IFR flight plan does not afford priority over VFR aircraft. For example, this does not preclude the requirement for the pilot of an arriving IFR aircraft to adjust his/her flight path, as necessary, to enter a traffic pattern in sequence with arriving VFR aircraft.
Provide air traffic control service to aircraft on a “first come, first served” basis as circumstances permit, except the following:
NOTE- It is solely the pilot’s prerogative to cancel an IFR flight plan. However, a pilot’s retention of an IFR flight plan does not afford priority over VFR aircraft. For example, this does not preclude the requirement for the pilot of an arriving IFR aircraft to adjust his/her flight path, as necessary, to enter a traffic pattern in sequence with arriving VFR aircraft.
- An aircraft in distress has the right of way over all other air traffic.
- Provide priority to civilian air ambulance flights “LIFEGUARD.” Air carrier/taxi usage of the “LIFEGUARD” call sign, indicates that operational priority is requested. When verbally requested, provide priority to military air evacuation flights (AIR EVAC, MED EVAC) and scheduled air carrier/air taxi flights. Assist the pilots of air ambulance/evacuation aircraft to avoid areas of significant weather and turbulent conditions. When requested by a pilot, provide notifications to expedite ground handling of patients, vital organs, or urgently needed medical materials.
- NOTE- It is recognized that heavy traffic flow may affect the controller’s ability to provide priority handling. However, without compromising safety, good judgment shall be used in each situation to facilitate the most expeditious movement of a lifeguard aircraft.
- Provide maximum assistance to SAR aircraft performing a SAR mission.
- Expedite the movement of presidential aircraft and entourage and any rescue support aircraft as well as related control messages when traffic conditions and communications facilities permit.
- NOTE- As used herein the terms presidential aircraft and entourage include aircraft and entourage of the President, Vice President, or other public figures when designated by the White House.
- Provide special handling, as required to expedite Flight Check aircraft.
- NOTE- It is recognized that unexpected wind conditions, weather, or heavy traffic flows may affect controller’s ability to provide priority or special handling at the specific time
- Expedite movement of NIGHT WATCH aircraft when NAOC (pronounced NA-YOCK) is indicated in the remarks section of the flight plan or in air/ground communications.
- NOTE- The term “NAOC” will not be a part of the call sign but may be used when the aircraft is airborne to indicate a request for special handling.
- Provide expeditious handling for any civil or military aircraft using the code name “FLYNET.”
- Provide expeditious handling of aircraft using the code name “Garden Plot” only when CARF notifies you that such priority is authorized. Refer any questions regarding flight procedures to CARF for resolution.
- NOTE- Garden Plot flights require priority movement and are coordinated by the military with CARF. State authority will contact the Regional Administrator to arrange for priority of National Guard troop movements within a particular state.
- Provide special handling for USAF aircraft engaged in aerial sampling missions using the code name “SAMP.”
- Provide maximum assistance to expedite the movement of interceptor aircraft on active air defense missions until the unknown aircraft is identified.
- Expedite movement of Special Air Mission aircraft when SCOOT is indicated in the remarks section of the flight plan or in air/ground communications.
- NOTE- The term “SCOOT” will not be part of the call sign but may be used when the aircraft is airborne to indicate a request for special handling.
- When requested, provide priority handling to TEAL and NOAA mission aircraft.
- NOTE- Priority handling may be requested by the pilot, or via telephone from CARCAH or the 53rd Weather Reconnaissance Squadron (53WRS) operations center personnel, or in the remarks section of the flight plan.
- IFR aircraft shall have priority over SVFR aircraft.
- Providing priority and special handling to expedite the movement of OPEN SKIES observation and demonstration flights.
NOTE- An OPEN SKIES aircraft has priority over all “regular” air traffic. “Regular” is defined as all aircraft traffic other than:
1. Emergencies.
2. Aircraft directly involved in presidential movement.
3. Forces or activities in actual combat.
4. Lifeguard, MED EVAC, AIR EVAC and active SAR missions.
1. Emergencies.
2. Aircraft directly involved in presidential movement.
3. Forces or activities in actual combat.
4. Lifeguard, MED EVAC, AIR EVAC and active SAR missions.
- Aircraft operating under the North American Route Program (NRP) and in airspace identified in the High Altitude Redesign (HAR) program, are not subject to route limiting restrictions (e.g., published preferred IFR routes, letter of agreement requirements, standard operating procedures).
- If able, provide priority handling to diverted flights. Priority handling may be requested via use of “DVRSN” in the remarks section of the flight plan or by the flight being placed on the Diversion Recovery Tool (DRT).
EXPEDITIOUS COMPLIANCE
- Use the word “immediately” only when expeditious compliance is required to avoid an imminent situation.
- Use the word “expedite” only when prompt compliance is required to avoid the development of an imminent situation. If an “expedite” climb or descent clearance is issued by ATC, and subsequently the altitude to maintain is changed or restated without an expedite instruction, the expedite instruction is canceled.
- In either case, if time permits, include the reason for this action.
SAFETY ALERT
Issue a safety alert to an aircraft if you are aware the aircraft is in a position/altitude which, in your judgment, places it in unsafe proximity to terrain, obstructions, or other aircraft. Once the pilot informs you action is being taken to resolve the situation, you may discontinue the issuance of further alerts. Do not assume that because someone else has responsibility for the aircraft that the unsafe situation has been observed and the safety alert issued; inform the appropriate controller.
NOTE- 1. The issuance of a safety alert is a first priority (see para 2-1-2, Duty Priority) once the controller observes and recognizes a situation of unsafe aircraft proximity to terrain, obstacles, or other aircraft. Conditions, such as workload, traffic volume, the quality/limitations of the radar system, and the available lead time to react are factors in determining whether it is reasonable for the controller to observe and recognize such situations. While a controller cannot see immediately the development of every situation where a safety alert must be issued, the controller must remain vigilant for such situations and issue a safety alert when the situation is recognized. 2. Recognition of situations of unsafe proximity may result from MSAW/E-MSAW/LAAS, automatic altitude readouts, Conflict/Mode C Intruder Alert, observations on a PAR scope, or pilot reports. 3. Once the alert is issued, it is solely the pilot’s prerogative to determine what course of action, if any, will be taken.
Issue a safety alert to an aircraft if you are aware the aircraft is in a position/altitude which, in your judgment, places it in unsafe proximity to terrain, obstructions, or other aircraft. Once the pilot informs you action is being taken to resolve the situation, you may discontinue the issuance of further alerts. Do not assume that because someone else has responsibility for the aircraft that the unsafe situation has been observed and the safety alert issued; inform the appropriate controller.
NOTE- 1. The issuance of a safety alert is a first priority (see para 2-1-2, Duty Priority) once the controller observes and recognizes a situation of unsafe aircraft proximity to terrain, obstacles, or other aircraft. Conditions, such as workload, traffic volume, the quality/limitations of the radar system, and the available lead time to react are factors in determining whether it is reasonable for the controller to observe and recognize such situations. While a controller cannot see immediately the development of every situation where a safety alert must be issued, the controller must remain vigilant for such situations and issue a safety alert when the situation is recognized. 2. Recognition of situations of unsafe proximity may result from MSAW/E-MSAW/LAAS, automatic altitude readouts, Conflict/Mode C Intruder Alert, observations on a PAR scope, or pilot reports. 3. Once the alert is issued, it is solely the pilot’s prerogative to determine what course of action, if any, will be taken.
- Terrain/Obstruction Alert. Immediately issue/initiate an alert to an aircraft if you are aware the aircraft is at an altitude which, in your judgment, places it in unsafe proximity to terrain/obstructions. Issue the alert as follows:
- PHRASEOLOGY- LOW ALTITUDE ALERT (call sign), CHECK YOUR ALTITUDE IMMEDIATELY.
- THE (as appropriate) MEA/MVA/MOCA/MIA IN YOUR AREA IS (altitude), or if an aircraft is past the final approach fix (nonprecision approach), or the outer marker, or the fix used in lieu of the outer marker (precision approach), and, if known, issue THE (as appropriate) MDA/DH IS (altitude).
- Aircraft Conflict/Mode C Intruder Alert. Immediately issue/initiate an alert to an aircraft if you are aware of another aircraft at an altitude which you believe places them in unsafe proximity. If feasible, offer the pilot an alternate course of action.
- When an alternate course of action is given, end the transmission with the word “immediately.”
PHRASEOLOGY- TRAFFIC ALERT (call sign) (position of aircraft) ADVISE YOU TURN LEFT/RIGHT (heading), and/or CLIMB/DESCEND (specific altitude if appropriate) IMMEDIATELY.
INFLIGHT EQUIPMENT MALFUNCTIONS
INFLIGHT EQUIPMENT MALFUNCTIONS
- When a pilot reports an inflight equipment malfunction, determine the nature and extent of any special handling desired.
NOTE- Inflight equipment malfunctions include partial or complete failure of equipment, which may affect either safety, separation standards, and/or the ability of the flight to proceed under IFR, or in Reduced Vertical Separation Minimum (RVSM) airspace, in the ATC system. Controllers may expect reports from pilots regarding VOR, TACAN, ADF, GPS, RVSM capability, or low frequency navigation receivers, impairment of air-ground communications capability, or other equipment deemed appropriate by the pilot (e.g., airborne weather radar). Pilots should communicate the nature and extent of any assistance desired from ATC.
- Provide the maximum assistance possible consistent with equipment, workload, and any special handling requested.
- Relay to other controllers or facilities who will subsequently handle the aircraft, all pertinent details concerning the aircraft and any special handling required or being provided.
MINIMUM FUEL
If an aircraft declares a state of “minimum fuel,” inform any facility to whom control jurisdiction is transferred of the minimum fuel problem and be alert for any occurrence which might delay the aircraft en route.
NOTE- Use of the term “minimum fuel” indicates recognition by a pilot that his/her fuel supply has reached a state where, upon reaching destination, he/she cannot accept any undue delay. This is not an emergency situation but merely an advisory that indicates an emergency situation is possible should any undue delay occur. A minimum fuel advisory does not imply a need for traffic priority. Common sense and good judgment will determine the extent of assistance to be given in minimum fuel situations. If, at any time, the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, the pilot should declare an emergency and report fuel remaining in minutes.
REPORTING ESSENTIAL FLIGHT INFORMATION
Report as soon as possible to the appropriate AFSS/FSS, airport manager’s office, ARTCC, approach control facility, operations office, or military operations office any information concerning components of the NAS or any flight conditions which may have an adverse effect on air safety.
NOTE- AFSSs/FSSs are responsible for classifying and disseminating Notices to Airmen.
NAVAID MALFUNCTIONS
a. When an aircraft reports a ground-based NAVAID malfunction, take the following actions:
1. Request a report from a second aircraft.
2. If the second aircraft reports normal operations, continue use and inform the first aircraft. Record the incident on FAA Form 7230-4 or appropriate military form.
3. If the second aircraft confirms the malfunction or in the absence of a second aircraft report, activate the standby equipment or request the monitor facility to activate.
4. If normal operation is reported after the standby equipment is activated, continue use, record the incident on FAA Form 7230-4 or appropriate military form, and notify technical operations personnel (the Systems Engineer of the ARTCC when an en route aid is involved).
5. If continued malfunction is reported after the standby equipment is activated or the standby equipment cannot be activated, inform technical operations personnel and request advice on whether or not the aid should be shut down. In the absence of a second aircraft report, advise the technical operations personnel of the time of the initial aircraft report and the estimated time a second aircraft report could be obtained.
b. When an aircraft reports a GPS anomaly, request the following information and/or take the following actions:
1. Record the following minimum information:
(a) Aircraft call sign and type.
(b) Location.
(c) Altitude.
(d) Date/time of occurrence.
2. Record the incident on FAA Form 7230-4 or appropriate military form.
3. Broadcast the anomaly report to other aircraft as necessary.
PHRASEOLOGY- ATTENTION ALL AIRCRAFT, GPS REPORTED UNRELIABLE IN VICINITY/AREA (position).
EXAMPLE- “Attention all aircraft, GPS reported unreliable in the area 30 miles south of Waco VOR.”
c. When an aircraft reports a Wide Area Augmentation System (WAAS) anomaly, request the following information and/or take the following actions:
1. Determine if the pilot has lost all WAAS service.
PHRASEOLOGY- ARE YOU RECEIVING ANY WAAS SERVICE?
2. If the pilot reports receipt of any WAAS service, acknowledge the report and continue normal operations.
3. If the pilot reports loss of all WAAS service, report as a GPS anomaly using procedures in subpara 2-1-10b.
USE OF MARSA
a. MARSA may only be applied to military operations specified in a letter of agreement or other appropriate FAA or military document.
NOTE- Application of MARSA is a military command prerogative. It will not be invoked indiscriminately by individual units or pilots. It will be used only for IFR operations requiring its use. Commands authorizing MARSA will ensure that its implementation and terms of use are documented and coordinated with the control agency having jurisdiction over the area in which the operations are conducted. Terms of use will assign responsibility and provide for separation among participating aircraft.
b. ATC facilities do not invoke or deny MARSA. Their sole responsibility concerning the use of MARSA is to provide separation between military aircraft engaged in MARSA operations and other nonparticipating IFR aircraft.
c. DOD shall ensure that military pilots requesting special-use airspace/ATCAAs have coordinated with the scheduling agency, have obtained approval for entry, and are familiar with the appropriate MARSA procedures. ATC is not responsible for determining which military aircraft are authorized to enter special-use airspace/ATCAAs.
MILITARY PROCEDURES
Military procedures in the form of additions, modifications, and exceptions to the basic FAA procedure are prescribed herein when a common procedure has not been attained or to fulfill a specific requirement. They shall be applied by:
a. ATC facilities operated by that military service.
EXAMPLE- 1. An Air Force facility providing service for an Air Force base would apply USAF procedures to all traffic regardless of class. 2. A Navy facility providing service for a Naval Air Station would apply USN procedures to all traffic regardless of class.
b. ATC facilities, regardless of their parent organization (FAA, USAF, USN, USA), supporting a designated military airport exclusively. This designation determines which military procedures are to be applied.
EXAMPLE- 1. An FAA facility supports a USAF base exclusively; USAF procedures are applied to all traffic at that base. 2. An FAA facility provides approach control service for a Naval Air Station as well as supporting a civil airport; basic FAA procedures are applied at both locations by the FAA facility. 3. A USAF facility supports a USAF base and provides approach control service to a satellite civilian airport; USAF procedures are applied at both locations by the USAF facility.
c. Other ATC facilities when specified in a letter of agreement.
EXAMPLE- A USAF unit is using a civil airport supported by an FAA facility- USAF procedures will be applied as specified in a letter of agreement between the unit and the FAA facility to the aircraft of the USAF unit. Basic FAA procedures will be applied to all other aircraft.
FORMATION FLIGHTS
a. Control formation flights as a single aircraft. When individual control is requested, issue advisory information which will assist the pilots in attaining separation. When pilot reports indicate separation has been established, issue control instructions as required.
NOTE- 1. Separation responsibility between aircraft within the formation during transition to individual control rests with the pilots concerned until standard separation has been attained. 2. Formation join-up and breakaway will be conducted in VFR weather conditions unless prior authorization has been obtained from ATC or individual control has been approved.
b. Military and civil formation flights in RVSM airspace.
1. Utilize RVSM separation standards for a formation flight, which consists of all RVSM approved aircraft.
2. Utilize non-RVSM separation standards for a formation flight above FL 290, which does not consist of all RVSM approved aircraft.
3. If aircraft are requesting to form a formation flight to FL 290 or above, the controller who issues the clearance creating the formation flight is responsible for ensuring that the proper equipment suffix is entered for the lead aircraft.
4. If the flight departs as a formation, and is requesting FL 290 or above, the first center sector shall ensure that the proper equipment suffix is entered.
5. If the formation flight is below FL 290 and later requests FL 290 or above, the controller receiving the RVSM altitude request shall ensure the proper equipment suffix is entered.
6. Upon break-up of the formation flight, the controller initiating the break-up shall ensure that all aircraft or flights are assigned their proper equipment suffix.
COORDINATE USE OF AIRSPACE
a. Ensure that the necessary coordination has been accomplished before you allow an aircraft under
your control to enter another controller’s area of jurisdiction.
b. Before you issue control instructions directly or relay through another source to an aircraft which is within another controller’s area of jurisdiction that will change that aircraft’s heading, route, speed, or altitude, ensure that coordination has been accomplished with each of the controllers listed below whose area of jurisdiction is affected by those instructions unless otherwise specified by a letter of agreement or a facility directive:
1. The controller within whose area of jurisdiction the control instructions will be issued.
2. The controller receiving the transfer of control.
3. Any intervening controller(s) through whose area of jurisdiction the aircraft will pass.
c. If you issue control instructions to an aircraft through a source other than another controller (e.g., ARINC, AFSS/FSS, another pilot) ensure that the necessary coordination has been accomplished with any controllers listed in subparas b1, 2, and 3, whose area of jurisdiction is affected by those instructions unless otherwise specified by a letter of agreement or a facility directive.
CONTROL TRANSFER
a. Transfer control of an aircraft in accordance with the following conditions:
1. At a prescribed or coordinated location, time, fix, or altitude; or,
2. At the time a radar handoff and frequency change to the receiving controller have been completed and when authorized by a facility directive or letter of agreement which specifies the type and extent of control that is transferred.
b. Transfer control of an aircraft only after eliminating any potential conflict with other aircraft for which you have separation responsibility.
c. Assume control of an aircraft only after it is in your area of jurisdiction unless specifically coordinated or as specified by letter of agreement or a facility directive.
SURFACE AREAS
a. Coordinate with the appropriate nonapproach control tower on an individual aircraft basis before issuing a clearance which would require flight within a surface area for which the tower has responsibility unless otherwise specified in a letter of agreement.
b. Coordinate with the appropriate control tower for transit authorization when you are providing radar traffic advisory service to an aircraft that will enter another facility’s airspace.
NOTE- The pilot is not expected to obtain his/her own authorization through each area when in contact with a radar facility.
c. Transfer communications to the appropriate facility, if required, prior to operation within a surface area for which the tower has responsibility.
RADIO COMMUNICATIONS TRANSFER
a. Transfer radio communications before an aircraft enters the receiving controller’s area of jurisdiction unless otherwise coordinated or specified by a letter of agreement or a facility directive.
b. Transfer radio communications by specifying the
following:
NOTE- Radio communications transfer procedures may be specified by a letter of agreement or contained in the route description of an MTR as published in the DOD Planning AP/1B (AP/3).
1. The facility name or location name and terminal function to be contacted. TERMINAL: Omit the location name when transferring communications to another controller within your facility; except when instructing the aircraft to change frequency for final approach guidance include the name of the facility.
2. Frequency to use except the following may be omitted:
(a) FSS frequency.
(b) Departure frequency if previously given or published on a SID chart for the procedure issued.
(c) TERMINAL: (1) Ground or local control frequency if in your opinion the pilot knows which frequency is in use. (2) The numbers preceding the decimal point if the ground control frequency is in the 121 MHz bandwidth.
EXAMPLE-
“Contact Tower.”
“Contact Ground.”
“Contact Ground Point Seven.”
“Contact Ground, One Two Zero Point Eight.”
“Contact Huntington Radio.”
“Contact Departure.”
“Contact Los Angeles Center, One Two Three Point Four.”
3. Time, fix, altitude, or specifically when to contact a facility. You may omit this when compliance is expected upon receipt.
NOTE- AIM, para 5-3-1, ARTCC Communications, informs pilots that they are expected to maintain a listening watch on the transferring controller’s frequency until the time, fix, or altitude specified.
PHRASEOLOGY- CONTACT (facility name or location name and terminal function), (frequency). If required, AT (time, fix, or altitude).
c. In situations where an operational advantage will be gained, and following coordination with the receiving controller, you may instruct aircraft on the ground to monitor the receiving controller’s frequency.
EXAMPLE-
“Monitor Tower.”
“Monitor Ground.”
“Monitor Ground Point Seven.”
“Monitor Ground, One Two Zero Point Eight.”
d. In situations where a sector has multiple frequencies or when sectors are combined using multiple frequencies and the aircraft will remain under your jurisdiction, transfer radio communication by specifying the following:
PHRASEOLOGY- (Identification) CHANGE TO MY FREQUENCY (state frequency).
EXAMPLE- “United two twenty-two change to my frequency one two three point four.”
e. Avoid issuing a frequency change to helicopters known to be single-piloted during air-taxiing, hovering, or low-level flight. Whenever possible, relay necessary control instructions until the pilot is able to change frequency.
NOTE- Most light helicopters are flown by one pilot and require the constant use of both hands and feet to maintain control. Although Flight Control Friction Devices assist the pilot, changing frequency near the ground could result in inadvertent ground contact and consequent loss of control. Pilots are expected to advise ATC of their single-pilot status if unable to comply with a frequency change.
f. In situations where the controller does not want the pilot to change frequency but the pilot is expecting or may want a frequency change, use the following phraseology.
PHRASEOLOGY- REMAIN THIS FREQUENCY.
OPERATIONAL REQUESTS Respond to a request from another controller, a pilot or vehicle operator by one of the following verbal means:
a. Restate the request in complete or abbreviated terms followed by the word “APPROVED.” The phraseology “APPROVED AS REQUESTED” may be substituted in lieu of a lengthy readback.
PHRASEOLOGY- (Requested operation) APPROVED. or APPROVED AS REQUESTED.
b. State restrictions followed by the word “APPROVED.”
PHRASEOLOGY- (Restriction and/or additional instructions, requested operation) APPROVED.
c. State the word “UNABLE” and, time permitting, a reason.
PHRASEOLOGY- UNABLE (requested operation). and when necessary, (reason and/or additional instructions.)
d. State the words “STAND BY.”
NOTE- “STAND BY” is not an approval or denial. The controller acknowledges the request and will respond at a later time.
WAKE TURBULENCE
a. Apply wake turbulence procedures to aircraft operating behind heavy jets/B757s and, where indicated, to small aircraft behind large aircraft.
NOTE- Para 5-5-4, Minima, specifies increased radar separation for small type aircraft landing behind large, heavy, or B757 aircraft because of the possible effects of wake turbulence.
b. The separation minima shall continue to touchdown for all IFR aircraft not making a visual approach or maintaining visual separation.
WAKE TURBULENCE CAUTIONARY ADVISORIES
a. Issue wake turbulence cautionary advisories and the position, altitude if known, and direction of flight of the heavy jet or B757 to:
1. TERMINAL. VFR aircraft not being radar vectored but are behind heavy jets or B757s.
2. IFR aircraft that accept a visual approach or visual separation.
3. TERMINAL. VFR arriving aircraft that have previously been radar vectored and the vectoring has been discontinued.
b. Issue cautionary information to any aircraft if in your opinion, wake turbulence may have an adverse effect on it. When traffic is known to be a heavy aircraft, include the word heavy in the description.
NOTE- Wake turbulence may be encountered by aircraft in flight as well as when operating on the airport movement area. Because wake turbulence is unpredictable, the controller is not responsible for anticipating its existence or effect. Although not mandatory during ground operations, controllers may use the words jet blast, propwash, or rotorwash, in lieu of wake turbulence, when issuing a caution advisory.
PHRASEOLOGY-CAUTION WAKE TURBULENCE (traffic information).
TRAFFIC ADVISORIES
Unless an aircraft is operating within Class A airspace or omission is requested by the pilot, issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima. Where no separation minima applies, such as for VFR aircraft outside of Class B/Class C airspace, or a TRSA, issue traffic advisories to those aircraft on your frequency when in your judgment their proximity warrants it. Provide this service as follows:
a. To radar identified aircraft:
1. Azimuth from aircraft in terms of the 12-hour clock, or
2. When rapidly maneuvering aircraft prevent accurate issuance of traffic as in 1 above, specify the direction from an aircraft’s position in terms of the eight cardinal compass points (N, NE, E, SE, S, SW, W, and NW). This method shall be terminated at the pilot’s request.
3. Distance from aircraft in miles.
4. Direction in which traffic is proceeding and/or relative movement of traffic.
NOTE- Relative movement includes closing, converging, parallel same direction, opposite direction, diverging, overtaking, crossing left to right, crossing right to left.
5. If known, type of aircraft and altitude.
PHRASEOLOGY- TRAFFIC, (number) O’CLOCK, or when appropriate, (direction) (number) MILES, (direction)-BOUND and/or (relative movement), and if known, (type of aircraft and altitude). or When appropriate, (type of aircraft and relative position), (number of feet) FEET ABOVE/BELOW YOU. If altitude is unknown, ALTITUDE UNKNOWN.
EXAMPLE- “Traffic, eleven o’clock, one zero miles, southbound, converging, Boeing Seven Twenty Seven, one seven thousand.” “Traffic, twelve o’clock, one five miles, opposite direction, altitude unknown.” “Traffic, ten o’clock, one two miles, southeast bound, one thousand feet below you.”
6. When requested by the pilot, issue radar vectors to assist in avoiding the traffic, provided the aircraft to be vectored is within your area of jurisdiction or coordination has been effected with the sector/facility in whose area the aircraft is operating.
7. If unable to provide vector service, inform the pilot.
8. Inform the pilot of the following when traffic you have issued is not reported in sight:
(a) The traffic is no factor.
(b) The traffic is no longer depicted on radar.
PHRASEOLOGY-TRAFFIC NO FACTOR/NO LONGER OBSERVED, or (number) O’CLOCK TRAFFIC NO FACTOR/NO LONGER OBSERVED, or (direction) TRAFFIC NO FACTOR/NO LONGER OBSERVED.
b. To aircraft that are not radar identified:
1. Distance and direction from fix.
2. Direction in which traffic is proceeding.
3. If known, type of aircraft and altitude.
4. ETA over the fix the aircraft is approaching, if appropriate.
PHRASEOLOGY- TRAFFIC, (number) MILES/MINUTES (direction) OF (airport or fix), (direction)-BOUND, and if known, (type of aircraft and altitude), ESTIMATED (fix) (time), or TRAFFIC, NUMEROUS AIRCRAFT VICINITY (location). If altitude is unknown, ALTITUDE UNKNOWN.
EXAMPLE- “Traffic, one zero miles east of Forsythe V-O-R, Southbound, M-D Eighty, descending to one six thousand.”
“Traffic, reported one zero miles west of Downey V-O-R, northbound, Apache, altitude unknown, estimated Joliet V-O-R one three one five.”
“Traffic, eight minutes west of Chicago Heights V-O-R, westbound, Mooney, eight thousand, estimated Joliet V-O-R two zero three five.”
“Traffic, numerous aircraft, vicinity of Delia airport.”
c. For aircraft displaying Mode C, not radar identified, issue indicated altitude.
EXAMPLE- “Traffic, one o’clock, six miles, eastbound, altitude indicates six thousand five hundred.”
BIRD ACTIVITY INFORMATION
a. Issue advisory information on pilot-reported, tower-observed, or radar-observed and pilot-verified bird activity. Include position, species or size of birds, if known, course of flight, and altitude. Do this for at least 15 minutes after receipt of such information from pilots or from adjacent facilities unless visual observation or subsequent reports reveal the activity is no longer a factor.
EXAMPLE- “Flock of geese, one o’clock, seven miles, northbound, last reported at four thousand.”
“Flock of small birds, southbound along Mohawk River, last reported at three thousand.”
“Numerous flocks of ducks, vicinity Lake Winnebago, altitude unknown.”
b. Relay bird activity information to adjacent facilities and to AFSSs/FSSs whenever it appears it will become a factor in their areas.
TRANSFER OF POSITION RESPONSIBILITY
The transfer of position responsibility shall be accomplished in accordance with the “Standard Operating Practice (SOP) for the Transfer of Position Responsibility,” and appropriate facility directives each time operational responsibility for a position is transferred from one specialist to another.
WHEELS DOWN CHECK
USA/USAF/USN : Remind aircraft to check wheels down on each approach unless the pilot has previously reported wheels down for that approach.
NOTE- The intent is solely to remind the pilot to lower the wheels, not to place responsibility on the controller.
a. Tower shall issue the wheels down check at an appropriate place in the pattern.
PHRASEOLOGY- CHECK WHEELS DOWN.
b. Approach/arrival control, GCA shall issue the wheels down check as follows:
1. To aircraft conducting ASR, PAR, or radar monitored approaches, before the aircraft starts descent on final approach.
2. To aircraft conducting instrument approaches
and remaining on the radar facility’s frequency, before the aircraft passes the outer marker/final approach fix.
PHRASEOLOGY- WHEELS SHOULD BE DOWN.
SUPERVISORY NOTIFICATION
Ensure supervisor/controller-in-charge (CIC) is aware of conditions which impact sector/position operations including, but not limited to, the following:
a. Weather.
b. Equipment status.
c. Potential sector overload.
d. Emergency situations.
e. Special flights/operations.
PILOT DEVIATION NOTIFICATION
When it appears that the actions of a pilot constitute a pilot deviation, notify the pilot, workload permitting.
PHRASEOLOGY- (Identification) POSSIBLE PILOT DEVIATION ADVISE YOU CONTACT (facility) AT (telephone number).
TCAS RESOLUTION ADVISORIES
a. When an aircraft under your control jurisdiction informs you that it is responding to a TCAS Resolution Advisory (RA), do not issue control instructions that are contrary to the RA procedure that a crew member has advised you that they are executing. Provide safety alerts regarding terrain or obstructions and traffic advisories for the aircraft responding to the RA and all other aircraft under your control jurisdiction, as appropriate.
b. Unless advised by other aircraft that they are also responding to a TCAS RA, do not assume that other aircraft in the proximity of the responding aircraft are involved in the RA maneuver or are aware of the responding aircraft’s intended maneuvers. Continue to provide control instructions, safety alerts, and traffic advisories as appropriate to such aircraft.
c. Once the responding aircraft has begun a maneuver in response to an RA, the controller is not responsible for providing standard separation between the aircraft that is responding to an RA and any other aircraft, airspace, terrain or obstructions. Responsibility for standard separation resumes when one of the following conditions are met:
1. The responding aircraft has returned to its assigned altitude, or
2. A crew member informs you that the TCAS maneuver is completed and you observe that standard separation has been reestablished, or
3. The responding aircraft has executed an alternate clearance and you observe that standard separation has been reestablished.
NOTE- 1. AC 120-55A, Air Carrier Operational Approval and Use of TCAS II, suggests pilots use the following phraseology to notify controllers during TCAS events. When a TCAS RA may affect an ATC clearance, inform ATC when beginning the maneuver, or as soon as workload permits.
EXAMPLE- 1. “New York Center, United 321, TCAS climb.”
NOTE- 2. When the RA has been resolved, the flight crew should advise ATC they are returning to their previously assigned clearance or subsequent amended clearance.
EXAMPLE- 2. “New York Center, United 321, clear of conflict, returning to assigned altitude.”
RVSM OPERATIONS
Controller responsibilities shall include but not be limited to the following:
a. Non-RVSM aircraft operating in RVSM airspace.
1. Ensure non-RVSM aircraft are not permitted in RVSM airspace unless they meet the criteria of excepted aircraft and are previously approved by the operations supervisor/controller-in-charge (CIC). The following aircraft are excepted: DOD, Lifeguard, manufacturer aircraft being flown for development/certification, and Foreign State aircraft. These exceptions are accommodated on a workload or traffic-permitting basis.
NOTE- The operations supervisor/CIC is responsible for system acceptance of a non-RVSM aircraft beyond the initial sector to sector coordination following the pilot request to access the airspace. Operations supervisor/CIC responsibilities are defined in FAA Order 7210.3, Chapter 6, Section 9, Reduced Vertical Separation Minimum (RVSM).
2. A non-RVSM exception designated by the DOD for special consideration via the DOD Priority Mission website shall be referred to as a STORM flight.
3. Ensure sector-to-sector coordination for all non-RVSM aircraft operations within RVSM airspace.
4. Inform the operational supervisor/CIC when a non-RVSM exception flight is denied clearance into RVSM airspace or is removed from RVSM airspace.
b. Non-RVSM aircraft transitioning RVSM airspace.
Ensure that operations supervisors/CICs are made aware when non-RVSM aircraft are transitioning through RVSM airspace.
c. Apply appropriate separation standards and remove any aircraft from RVSM airspace that advises it is unable RVSM due to equipment while en route.
d. Use “negative RVSM” in all verbal ground-to-ground communications involving non-RVSM aircraft while cleared to operate within RVSM airspace.
EXAMPLE- “Point out Baxter21 climbing to FL 360, negative RVSM.”
e. For the following situations, use the associated phraseology:
1. To deny clearance into RVSM airspace.
PHRASEOLOGY- “UNABLE CLEARANCE INTO RVSM AIRSPACE.”
2. To request a pilot to report when able to resume RVSM.
PHRASEOLOGY- “REPORT ABLE TO RESUME RVSM.”
f. In the event of a change to an aircraft’s navigational capability amend the equipment suffix in order to properly identify non-RVSM aircraft on the controller display.
TERRAIN AWARENESS WARNING SYSTEM (TAWS) ALERTS
a. When an aircraft under your control jurisdiction informs you that it is responding to a TAWS (or other on-board low altitude) alert, do not issue control instructions that are contrary to the TAWS procedure that a crew member has advised you that they are executing. Provide safety alerts regarding terrain or obstructions and traffic advisories for the aircraft responding to the TAWS alert and all other aircraft under your control jurisdiction, as appropriate.
b. Once the responding aircraft has begun a maneuver in response to TAWS alert, the controller is not responsible for providing standard separation between the aircraft that is responding to a TAWS alert and any other aircraft, airspace, terrain or obstructions. Responsibility for standard separation resumes when one of the following conditions are met:
1. The responding aircraft has returned to its assigned altitude, or
2. A crew member informs you that the TAWS maneuver is completed and you observe that standard separation has been reestablished, or
3. The responding aircraft has executed an alternate clearance and you observe that standard separation has been reestablished.
Flight Plans and Control Information
RECORDING INFORMATION
a. Record flight plan information required by the type of flight plan and existing circumstances. Use authorized abbreviations when possible.
NOTE- Generally, all military overseas flights are required to clear through a specified military base operations office (BASOPS). Pilots normally will not file flight plans directly with an FAA facility unless a BASOPS is not available. BASOPS will, in turn, forward the IFR flight notification message to the appropriate center.
b. EN ROUTE. When flight plans are filed directly with the center, record all items given by the pilot either on a flight progress strip/flight data entry or on a voice recorder. If the latter, enter in box 26 of the initial flight progress strip the sector or position number to identify where the information may be found in the event search and rescue (SAR) activities become necessary.
FORWARDING INFORMATION
a. Except during EAS FDP operation, forward the flight plan information to the appropriate ATC facility, AFSS/FSS, or BASOPS and record the time of filing and delivery on the form.
b. EN ROUTE. During EAS FDP operation, the above manual actions are required in cases where the data is not forwarded automatically by the computer.
NOTE- During EAS FDP operation, data is exchanged between interfaced automated facilities and both the data and time of transmission are recorded automatically.
c. EN ROUTE. Forward proposed tower en route flight plans and any related amendments to the appropriate departure terminal facility.
FORWARDING VFR DATA
TERMINAL : Forward aircraft departure times to AFSSs/FSSs or military operations offices when they have requested them. Forward other VFR flight plan data only if requested by the pilot.
MILITARY DVFR DEPARTURES
TERMINAL : Forward departure times on all military DVFR departures from joint-use airports to the military operations office.
NOTE- 1. Details for handling air carrier, nonscheduled civil, and military DVFR flight data are contained in FAAO JO 7610.4, Special Operations. 2. Military pilots departing DVFR from a joint-use airport will include the phrase “DVFR to (destination)” in their initial call-up to an FAA operated tower.
IFR TO VFR FLIGHT PLAN CHANGE
Request a pilot to contact the appropriate AFSS/FSS if the pilot informs you of a desire to change from an IFR to a VFR flight plan.
IFR FLIGHT PROGRESS DATA
Forward control information from controller to controller within a facility, then to the receiving facility as the aircraft progresses along its route. Where appropriate, use computer equipment in lieu of manual coordination procedures. Do not use the remarks section of flight progress strips in lieu of voice coordination to pass control information. Ensure that flight plan and control information is correct and up-to-date. When covered by a letter of agreement/facility directive, the time requirements of subpara a may be reduced, and the time requirements of subpara b1 and para 2-2-11, Forwarding Amended and UTM Data, subpara a may be increased up to 15 minutes when facilitated by automated systems or mandatory radar handoffs; or if operationally necessary because of manual data processing or nonradar operations, the time requirements of subpara a may be increased.
NOTE- 1. The procedures for preparing flight plan and control information related to altitude reservations (ALTRVs) are contained in FAAO JO 7210.3, para 8-1-2, Facility Operation and Administration, ALTRV Flight Data Processing. Development of the methods for assuring the accuracy and completeness of ALTRV flight plan and control information is the responsibility of the military liaison and security officer. 2. The term facility in this paragraph refers to centers and terminal facilities when operating in an en route capacity.
a. Forward the following information at least 15 minutes before the aircraft is estimated to enter the receiving facility’s area:
1. Aircraft identification.
2. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
3. Assigned altitude and ETA over last reporting point/fix in transferring facility’s area or assumed departure time when the departure point is the last point/fix in the transferring facility’s area.
4. Altitude at which aircraft will enter the receiving facility’s area if other than the assigned altitude.
5. True airspeed.
6. Point of departure.
7. Route of flight remaining.
8. Destination airport and clearance limit if other than destination airport.
9. ETA at destination airport (not required for military or scheduled air carrier aircraft).
10. Altitude requested by the aircraft if assigned altitude differs from requested altitude (within a facility only).
NOTE- When an aircraft has crossed one facility’s area and assignment at a different altitude is still desired, the pilot will reinitiate the request with the next facility.
11. When flight plan data must be forwarded manually and an aircraft has been assigned a beacon code by the computer, include the code as part of the flight plan.
NOTE- When an IFR aircraft, or a VFR aircraft that has been assigned a beacon code by the EAS and whose flight plan will terminate in another facility’s area, cancels ATC service or does not activate the flight plan, send a remove strips (RS) message on that aircraft via the EAS keyboard, the FDIO keyboard or call via service F.
12. Longitudinal separation being used between aircraft at the same altitude if it results in these aircraft having less than 10 minutes separation at the facilities’ boundary.
13. Any additional nonroutine operational information pertinent to flight safety.
NOTE- EN ROUTE. This includes alerting the receiving controller that the flight is conducting celestial navigation training.
b. Forward position report over last reporting point in the transferring facility’s area if any of the following conditions exist:
1. Time differs more than 3 minutes from estimate given.
2. Requested by receiving facility.
3. Agreed to between facilities.
MANUAL INPUT OF COMPUTER-ASSIGNED BEACON CODES
When a flight plan is manually entered into the computer and a computer-assigned beacon code has been forwarded with the flight plan data, insert the beacon code in the appropriate field as part of the input message.
ALTRV INFORMATION
EN ROUTE : When an aircraft is a part of an approved ALTRV, forward only those items necessary to properly identify the flight, update flight data contained in the ALTRV APVL, or revise previously given information.
COMPUTER MESSAGE VERIFICATION
EN ROUTE : Unless your facility is equipped to automatically obtain acknowledgment of receipt of transferred data, when you transfer control information by computer message, obtain, via Service F, acknowledgment that the receiving center has received the message and verification of the following:
a. Within the time limits specified by a letter of agreement or when not covered by a letter of agreement, at least 15 minutes before the aircraft is estimated to enter the receiving facility’s area, or at the time of a radar handoff, or coordination for transfer of control:
1. Aircraft identification.
2. Assigned altitude.
3. Departure or coordination fix time.
b. Any cancellation of IFR or EAS generated VFR flight plan.
TRANSMIT PROPOSED FLIGHT PLAN
EN ROUTE
a. Transmit proposed flight plans which fall within an ARTCC’s Proposed Boundary Crossing Time (PBCT) parameter to adjacent ARTCC’s via the Computer B network during hours of inter-center computer operation. In addition, when the route of flight of any proposed flight plan exceeds 20 elements external to the originating ARTCC’s area, NADIN shall be used to forward the data to all affected centers.
b. During nonautomated operation, the proposed flight plans shall be sent via NADIN to the other centers involved when any of the following conditions are met:
1. The route of flight external to the originating center’s area consists of 10 or more elements and the flight will enter 3 or more other center areas.
NOTE- An element is defined as either a fix or route as specified in FAAO JO 7110.10, Flight Services, para 6-3-3, IFR Flight Plan Control Messages.
2. The route of flight beyond the first point of exit from the originating center’s area consists of 10 or more elements, which are primarily fixes described in fix-radial-distance or latitude/longitude format, regardless of the number of other center areas entered.
3. The flight plan remarks are too lengthy for interphone transmission.
FORWARDING AMENDED AND UTM DATA
a. Forward any amending data concerning previously forwarded flight plans except that revisions to ETA information in para 2-2-6, IFR Flight Progress Data, need only be forwarded when the time differs by more than 3 minutes from the estimate given.
PHRASEOLOGY- (Identification), REVISED (revised information).
EXAMPLE- “American Two, revised flight level, three three zero.”
“United Eight Ten, revised estimate, Front Royal two zero zero five.”
“Douglas Five Zero One Romeo, revised altitude, eight thousand.”
“U.S. Air Eleven Fifty-one, revised type, heavy Boeing Seven Sixty-seven.”
b. Computer acceptance of an appropriate input message fulfills the requirement for sending amended data. During EAS FDP operations, the amendment data are considered acknowledged on receipt of a computer update message or a computer-generated flight progress strip containing the amended data.
NOTE- 1. The successful utilization of automation equipment requires timely and accurate insertion of changes and/or new data. 2. If a pilot is not issued a computer-generated PDR/PDAR/PAR and if amendment data is not entered into the computer, the next controller will have incorrect route information.
c. Forward any amended control information and record the action on the appropriate flight progress strip. Additionally, when a route or altitude in a previously issued clearance is amended within 15 minutes of an aircraft’s proposed departure time, the facility that amended the clearance shall coordinate the amendment with the receiving facility via verbal AND automated means to ensure timely passage of the information.
NOTE- The term “receiving” facility means the ATC facility that is expected to transmit the amended clearance to the intended aircraft/pilot.
d. EN ROUTE. Effect manual coordination on any interfacility flight plan data that is not passed through automated means.
AIRBORNE MILITARY FLIGHTS
Forward to AFSSs/FSSs the following information received from airborne military aircraft:
a. IFR flight plans and changes from VFR to IFR flight plans.
b. Changes to an IFR flight plan as follows:
1. Change in destination:
(a) Aircraft identification and type.
(b) Departure point.
(c) Original destination.
(d) Position and time.
(e) New destination.
(f) ETA.
(g) Remarks including change in fuel exhaustion time.
(h) Revised ETA.
2. Change in fuel exhaustion time.
NOTE- This makes current information available to AFSSs/FSSs for relay to military bases concerned and for use by centers in the event of two-way radio communications failure.
FORWARDING FLIGHT PLAN DATA BETWEEN U.S. ARTCCs AND CANADIAN ACCs
EN ROUTE
a. Domestic. (Continental U.S./Canadian airspace except Alaska) Proposed departure flight plans and en route estimates will be handled on a 30 minute lead time (or as bilaterally agreed) between any ACC and ARTCC.
b. International. Any route changes (except SIDs) must be forwarded to the appropriate Oceanic/Pre-oceanic ACC or ARTCC with an optimum lead time of 30 minutes or as soon as this information becomes available.
c. Initially, if a flight goes from U.S. airspace into Canadian airspace and returns to U.S. airspace, the ACC will be responsible for forwarding the flight plan data to the appropriate ARTCC by voice transmission except for flights which traverse mutually agreed on airways/fixes. These airways/fixes will be determined on a case-by-case basis and will be based on time and distance considerations at the service area office.
TELETYPE FLIGHT DATA FORMAT- U.S. ARTCCs - CANADIAN ACCs
EN ROUTE : The exchange of flight plan data between Canadian ACCs and U.S. ARTCCs shall be made as follows:
a. The U.S. ARTCCs will transmit flight data to the Canadian ACCs in one of the following formats:
1. NADIN II input format as described in the NAS Management Directives (MDs) for:
(a) Flight Plan Messages: (1) Active. (2) Proposed.
(b) Amendment messages.
(c) Cancellation messages.
(d) Response Messages to Canadian Input:
(1) Acknowledgment messages. (2) Error messages. (3) Rejection messages.
2. Transport Canada (TC) ACC Flight Strip Format: Where the data to be printed on the ACC strip form exceeds the strip form field size, the NADIN II input format in 1 above will be used. Input sequentially fields 1 through 8 in para 2-2-6, IFR Flight Progress Data, subpara a.
b. TC’s ACCs will transmit flight data to the FAA ARTCCs in the following format:
1. NADIN II input format as described in NAS MDs for:
(a) Flight Plan Messages: (1) Active. (2) Proposed.
(b) Amendment messages.
(c) Cancellation messages.
(d) Correction messages.
NORTH AMERICAN ROUTE PROGRAM (NRP) INFORMATION
a. “NRP” shall be retained in the remarks section of the flight plan if the aircraft is moved due to weather, traffic, or other tactical reasons.
NOTE- Every effort should be made to ensure the aircraft is returned to the original filed flight plan/altitude as soon as conditions warrant.
b. If the route of flight is altered due to a pilot request, “NRP” shall be removed from the remarks section of the flight plan.
c. “NRP” shall not be entered in the remarks section of a flight plan, unless prior coordination is accomplished with the ATCSCC or as prescribed by international NRP flight operations procedures.
d. The en route facility within which an international flight entering the conterminous U.S. requests to participate in the NRP shall enter “NRP” in the remarks section of the flight plan.
Flight Progress Strips
GENERAL - Unless otherwise authorized in a facility directive, use flight progress strips to post current data on air traffic and clearances required for control and other air traffic control services. To prevent misinterpretation when data is hand printed, use standard hand-printed characters.
En route: Flight progress strips shall be posted.
a. Maintain only necessary current data and remove the strips from the flight progress boards when no longer required for control purposes. To correct, update, or preplan information:
1. Do not erase or overwrite any item. Use an “X” to delete a climb/descend and maintain arrow, an at or above/below symbol, a cruise symbol, and unwanted altitude information. Write the new altitude information immediately adjacent to it and within the same space.
2. Do not draw a horizontal line through an altitude being vacated until after the aircraft has reported or is observed (valid Mode C) leaving the altitude.
3. Preplanning may be accomplished in red pencil.
b. Manually prepared strips shall conform to the format of machine-generated strips and manual strip preparation procedures will be modified simultaneously with the operational implementation of changes in the machine-generated format.
c. Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e. 5,000 feet as 5, and 2,800 as 2.8.
NOTE- A slant line crossing through the number zero and underline of the letter “s” on handwritten portions of flight progress strips are required only when there is reason to believe the lack of these markings could lead to misunderstanding. A slant line crossing through the number zero is required on all weather data.
EN ROUTE DATA ENTRIES
a. Information recorded on the flight progress strips (FAA Forms 7230-19) shall be entered in the correspondingly numbered spaces:
Block Information Recorded
1. Verification symbol if required.
2. Revision number.DSR-Not used.
3. Aircraft identification.
4. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
5. Filed true airspeed.
6. Sector number.
7. Computer identification number if required.
8. Estimated ground speed.
9. Revised ground speed or strip request (SR) originator.
10. Strip number.DSR- Strip number/Revision number.
11. Previous fix.
12. Estimated time over previous fix.
13. Revised estimated time over previous fix.
14. Actual time over previous fix, or actual departure time entered on first fix posting after departure.
14a. Plus time expressed in minutes from the previous fix to the posted fix.
15. Center-estimated time over fix (in hours and minutes), or clearance information for departing aircraft.
16. Arrows to indicate if aircraft is departing (‘!) or arriving (“!).
17. Pilot-estimated time over fix.
18. Actual time over fix, time leaving holding fix, arrival time at nonapproach control airport, or symbol indicating cancellation of IFR flight plan for arriving aircraft, or departure time (actual or assumed).
19. Fix. For departing aircraft, add proposed departure time.
20. Altitude information (in hundreds of feet) or as noted below.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e. FL 330 as 33, 5,000 feet as 5, and 2,800 as 2.8.
20a. OPTIONAL USE, when voice recorders are operational;REQUIRED USE, when the voice recorders are not operating and strips are being use at the facility. This space is used to record reported RA events. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
21. Next posted fix or coordination fix.
22. Pilot’s estimated time over next fix.
23. Arrows to indicate north (‘!), south (“!), east (’!), or west (!) direction of flight if required.
24. Requested altitude.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e., FL 330 as 33, 5,000 feet as 5, and 2,800 as 2.8.
25. Point of origin, route as required for control and data relay, and destination.
26. Pertinent remarks, minimum fuel, point out/radar vector/speed adjustment information or sector/position number (when applicable in accordance with para 2-2-1, Recording Information), or NRP. High Altitude Redesign (HAR) or Point-to-point (PTP) may be used at facilities actively using these programs.
27. Mode 3/A beacon code if applicable.
28. Miscellaneous control data (expected further clearance time, time cleared for approach, etc.).
29-30. Transfer of control data and coordination indicators.
b. Latitude/longitude coordinates may be used to define waypoints and may be substituted for nonadapted NAVAIDs in space 25 of domestic en route flight progress strips provided it is necessary to accommodate a random RNAV or GNSS route request.
c. Facility air traffic managers may authorize the optional use of spaces 13, 14, 14a, 22, 23, 24, and 28 for point out information, radar vector information, speed adjustment information, or transfer of control data.
OCEANIC DATA ENTRIES
a. The Ocean21 system displays information on electronic flight progress strips and, in the event of a catastrophic system failure, will print flight progress strips with data in the corresponding numbered spaces:
Block Information Recorded
1. Mode 3/A beacon code, if applicable.
2. Number of aircraft, if more than one, and type of aircraft.
3. Aircraft identification.
4. Reduced separation flags. Indicators are available for:
M - Mach Number Technique (MNT), R - Reduced MNT,D or 3 - Distance-based longitudinal separation using 50 NM (D) or 30 NM (3), andW- Reduced Vertical Separation Minimum (RVSM).These flags are selectable for aircraft whose flight plans contain the required equipment qualifiers for each separation criteria.
5. Controlling sector number.
6. Filed airspeed or assigned Mach number/True airspeed.
7. Reported flight level. May contain an indicator for a flight that is climbing (‘!) or descending (“!). Reports from Mode C, ADS or position reports are displayed in that order of preference.
8. Cleared flight level. May contain an indicator for a future conditional altitude ( * ) that cannot be displayed.
9. Requested flight level, if applicable.
10. Previously reported position.
11. Actual time over previously reported position.
12. Last reported position.
13. Actual time over last reported position.
14. Next reporting position.
15. In-conformance pilot’s estimate or controller-accepted pilot’s estimate for next reporting position.
16. Future reporting position(s).
17. System estimate for future reporting position(s).
18. Departure airport or point of origin.
19. Destination airport or filed point of flight termination.
20. Indicators. Indicators and toggles for displaying or suppressing the display of the route of flight (F), second flight profile (2), radar contact (A), annotations (&), degraded Required Navigation Performance (RNP, indicator R) and clearance restrictions (X).
21. Coordination indicator(s).
22. Annotations.
23. Clearance restrictions and conditions (may be multiple lines).
24. Strip number and total number of strips (printed strips only).
b. Standard annotations and abbreviations for Field 22 may be specified by facility directives.
TERMINAL DATA ENTRIES
a. Arrivals: Information recorded on the flight progress strips (FAA Forms 7230-7.1, 7230-7.2, and 7230-8) shall be entered in the correspondingly numbered spaces. Facility managers can authorize omissions and/or optional use of spaces 2A, 8A, 8B, 9A, 9B, 9C, and 10-18, if no misunderstanding will result. These omissions and/or optional uses shall be specified in a facility directive.
Block Information Recorded
1. Aircraft identification.
2. Revision number (FDIO locations only).
2A. Strip request originator. (At FDIO locations this indicates the sector or position that requested a strip be printed.)
3. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
4. Computer identification number if required.
5. Secondary radar (beacon) code assigned.
6. (FDIO Locations.) The previous fix will be printed.(Non-FDIO Locations.) Use of the inbound airway. This function is restricted to facilities where flight data is received via interphone when agreed upon by the center and terminal facilities.
7. Coordination fix.
8. Estimated time of arrival at the coordination fix or destination airport.
8A. OPTIONAL USE.
8B. OPTIONAL USE, when voice recorders are operational; REQUIRED USE, when the voice recorders are not operating and strips are being used at the facility. This space is used to record reported RA events when the voice recorders are not operational and strips are being used at the facility. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
9. Altitude (in hundreds of feet) and remarks.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i. e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
9A. Minimum fuel, destination airport/point out/radar vector/speed adjustment information. Air traffic managers may authorize in a facility directive the omission of any of these items, except minimum fuel, if no misunderstanding will result.
NOTE- Authorized omissions and optional use of spaces shall be specified in the facility directive concerning strip marking procedures.
9B. OPTIONAL USE.
9C. OPTIONAL USE.
10-18. Enter data as specified by a facility directive. Radar facility personnel need not enter data in these spaces except when nonradar procedures are used or when radio recording equipment is inoperative.
b. Departures: Information recorded on the flight progress strips (FAA Forms 7230-7.1, 7230-7.2, and 7230-8) shall be entered in the correspondingly numbered spaces. Facility managers can authorize omissions and/or optional use of spaces 2A, 8A, 8B, 9A, 9B, 9C, and 10-18, if no misunderstanding will result. These omissions and/or optional uses shall be specified in a facility directive.
Block Information Recorded
1. Aircraft identification.
2. Revision number (FDIO locations only).
2A. Strip request originator. (At FDIO locations this indicates the sector or position that requested a strip be printed.)
3. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
4. Computer identification number if required.
5. Secondary radar (beacon) code assigned.
6. Proposed departure time.
7. Requested altitude.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i. e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
8. Departure airport.
8A. OPTIONAL USE.
8B. OPTIONAL USE, when voice recorders are operational;
REQUIRED USE, when the voice recorders are not operating and strips are being used at the facility. This space is used to record reported RA events when the voice recorders are not operational and strips are being used at the facility. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
9. Computer-generated: Route, destination, and remarks. Manually enter altitude/altitude restrictions in the order flown, if appropriate, and remarks.
9. Hand-prepared: Clearance limit, route, altitude/altitude restrictions in the order flown, if appropriate, and remarks.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
9A. OPTIONAL USE.
9B. OPTIONAL USE.
9C. OPTIONAL USE.
10-18. Enter data as specified by a facility directive. Items, such as departure time, runway used for takeoff, check marks to indicate information forwarded or relayed, may be entered in these spaces.
c. Overflights: Information recorded on the flight progress strips (FAA Forms 7230-7.1, 7230-7.2, and 7230-8) shall be entered in the correspondingly numbered spaces. Facility managers can authorize omissions and/or optional use of spaces 2A, 8A, 8B, 9A, 9B, 9C, and 10-18, if no misunderstanding will result. These omissions and/or optional uses shall be specified in a facility directive.
Block Information Recorded
1. Aircraft identification.
2. Revision number (FDIO locations only).
2A. Strip request originator. (At FDIO locations this indicates the sector or position that requested a strip be printed.)
3. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
4. Computer identification number if required.
5. Secondary radar (beacon) code assigned.
6. Coordination fix.
7. Overflight coordination indicator (FDIO locations only).
NOTE- The overflight coordination indicator identifies the facility to which flight data has been forwarded.
8. Estimated time of arrival at the coordination fix.
8A. OPTIONAL USE.
8B. OPTIONAL USE, when voice recorders are operational;
REQUIRED USE, when the voice recorders are not operating and strips are being used at the facility. This space is used to record reported RA events when the voice recorders are not operational and strips are being used at the facility. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
9. Altitude and route of flight through the terminal area.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
9A. OPTIONAL USE.
9B. OPTIONAL USE.
9C. OPTIONAL USE.
10-18. Enter data as specified by a facility directive.
NOTE- National standardization of items (10 through 18) is not practical because of regional and local variations in operating methods; e.g., single fix, multiple fix, radar, tower en route control, etc.
d. Air traffic managers at automated terminal radar facilities may waive the requirement to use flight progress strips provided:
1. Backup systems such as multiple radar sites/systems or single site radars with CENRAP are utilized.
2. Local procedures are documented in a facility directive. These procedures should include but not be limited to:
(a) Departure areas and/or procedures.
(b) Arrival procedures.
(c) Overflight handling procedures.
(d) Transition from radar to nonradar.
(e) Transition from ARTS to non-ARTS.
(f) Transition from ASR to CENRAP.
(g) Transition to or from ESL.
3. No misunderstanding will occur as a result of no strip usage.
4. Unused flight progress strips, facility developed forms and/or blank notepads shall be provided for controller use.
5. Facilities shall revert to flight progress strip usage if backup systems referred to in subpara d1 are not available.
e. Air traffic managers at FDIO locations may authorize reduced lateral spacing between fields so as to print all FDIO data to the left of the strip perforation. When using FAA Form 7230-7.2, all items will retain the same relationship to each other as they do when the full length strip (FAA Form 7230-7.1) is used.
AIRCRAFT IDENTITY
Indicate aircraft identity by one of the following using combinations not to exceed seven alphanumeric characters:
a. Civil aircraft, including air-carrier aircraft letter-digit registration number including the letter “T” prefix for air taxi aircraft, the letter “L” for lifeguard aircraft, 3-letter aircraft company designator specified in FAAO JO 7340.2, Contractions, followed by the trip or flight number. Use the operating air carrier’s company name in identifying equipment interchange flights.
EXAMPLE-
“N12345.”
“TN5552Q.”
“AAl192.”
“LN751B.”
NOTE- The letter “L” is not to be used for air carrier/air taxi lifeguard aircraft.
b. Military Aircraft.
1. Prefixes indicating branch of service and/or type of mission followed by the last 5 digits of the serial number (the last 4 digits for CFC and CTG).
2. Pronounceable words of 3, 4, 5, and 6 letters followed by a 4-, 3-, 2-, or 1-digit number.
EXAMPLE- “SAMP Three One Six.”
3. Assigned double-letter 2-digit flight number.
4. Navy or Marine fleet and training command aircraft, one of the following:
(a) The service prefix and 2 letters (use phonetic alphabet equivalent) followed by 2 or 3 digits.
Branch of Service Prefix
Prefix Branch
A U.S. Air Force
C U.S. Coast Guard
G Air or Army National Guard
R U.S. Army
VM U.S. Marine Corps
VV U.S. Navy
CFC Canadian Forces
CTG Canadian Coast Guard
Military Mission Prefix
Prefix Mission
E Medical Air Evacuation
F Flight Check
L LOGAIR (USAF Contract)
RCH AMC (Air Mobility Command)
S Special Air Mission
(b) The service prefix and a digit and a letter (use phonetic alphabet equivalent) followed by 2 or 3 digits.
c. Special-use. Approved special-use identifiers.
REDUCED VERTICAL SEPARATION MINIMUM (RVSM). Prior to conducting RVSM operations within the U.S., the operator must obtain authorization from the FAA or from the responsible authority, as appropriate.
/J /E with RVSM
/K /F with RVSM
/L /G with RVSM
/Q /R with RVSM
/W RVSM
Clearance Abbreviations
Abbreviation Meaning
A Cleared to airport (point of intended landing)
B Center clearance delivered
C ATC clears (when clearance relayed through non-ATC facility)
CAF Cleared as filed
D Cleared to depart from the fix
F Cleared to the fix
H Cleared to hold and instructions issued
L Cleared to land
N Clearance not delivered
O Cleared to the outer marker
PD Cleared to climb/descend at pilot’s discretion
Q Cleared to fly specified sectors of a NAVAID defined in terms of courses, bearings, radials or quadrants within a designated radius.
T Cleared through (for landing and takeoff through intermediate point)
V Cleared over the fix
X Cleared to cross (airway, route, radial) at (point)
Z Tower jurisdiction
Miscellaneous Abbreviations
Abbreviation Meaning
BC Back course approach
CT Contact approach
FA Final approach
FMS Flight management system approach
GPS GPS approach
I Initial approach
ILS ILS approach
MA Missed approach
MLS MLS approach
NDB Nondirectional radio beacon approach
OTP VFR conditions-on-top
PA Precision approach
PT Procedure turn
RA Resolution advisory (Pilot reported TCAS event)
RH Runway heading
RNAV Area navigation approach
RP Report immediately upon passing (fix/altitude)
RX Report crossing
SA Surveillance approach
SI Straight-in approach
TA TACAN approach
TL Turn left
TR Turn right
VA Visual approach
VR VOR approach
11
Radio and Interphone Communications
RADIO COMMUNICATIONS
Use radio frequencies for the special purposes for which they are intended. A single frequency may be used for more than one function except as follows:
TERMINAL. When combining positions in the tower, do not use ground control frequency for airborne communications.
NOTE- Due to the limited number of frequencies assigned to towers for the ground control function, it is very likely that airborne use of a ground control frequency could cause interference to other towers or interference to your aircraft from another tower. When combining these functions, it is recommended combining them on local control. The ATIS may be used to specify the desired frequency.
MONITORING
Monitor interphones and assigned radio frequencies continuously.
NOTE- Although all FAA facilities, including RAPCONs and RATCFs, are required to monitor all assigned frequencies continuously, USAF facilities may not monitor all unpublished discrete frequencies.
PILOT ACKNOWLEDGMENT/READ BACK
a. When issuing clearances or instructions ensure acknowledgment by the pilot.
NOTE- Pilots may acknowledge clearances, instructions, or other information by using “Wilco,” “Roger,” “Affirmative,” or other words or remarks.
b. If altitude, heading, or other items are read back by the pilot, ensure the read back is correct. If incorrect or incomplete, make corrections as appropriate.
AUTHORIZED INTERRUPTIONS
As necessary, authorize a pilot to interrupt his/her communications guard.
NOTE- Some users have adopted procedures to insure uninterrupted receiving capability with ATC when a pilot with only one operative communications radio must interrupt his/her communications guard because of a safety related problem requiring airborne communications with his/her company. In this event, pilots will request approval to abandon guard on the assigned ATC frequency for a mutually agreeable time period. Additionally, they will inform controllers of the NAVAID voice facility and the company frequency they will monitor.
AUTHORIZED TRANSMISSIONS
Transmit only those messages necessary for air traffic control or otherwise contributing to air safety.
FALSE OR DECEPTIVE COMMUNICATIONS
Take action to detect, prevent, and report false, deceptive, or phantom controller communications to an aircraft or controller. The following shall be accomplished when false or deceptive communications occur:
a. Correct false information.
b. Broadcast an alert to aircraft operating on all frequencies within the area where deceptive or phantom transmissions have been received.
EXAMPLE- “Attention all aircraft. False ATC instructions have been received in the area of Long Beach Airport. Exercise extreme caution on all frequencies and verify instructions.”
c. Collect pertinent information regarding the incident.
d. Notify the operations supervisor of the false, deceptive, or phantom transmission and report all relevant information pertaining to the incident.
AUTHORIZED RELAYS
a. Relay operational information to aircraft or aircraft operators as necessary. Do not agree to handle such messages on a regular basis. Give the source of any such message you relay.
b. Relay official FAA messages as required.
NOTE- The FAA Administrator and Deputy Administrator will sometimes use code phrases to identify themselves in air-to-ground communications as follows:
Administrator: “SAFEAIR ONE.”
Deputy Administrator: “SAFEAIR TWO.”
EXAMPLE- “Miami Center, Jetstar One, this is SAFEAIR ONE, (message).”
c. Relay operational information to military aircraft operating on, or planning to operate on IRs.
RADIO MESSAGE FORMAT
Use the following format for radio communications with an aircraft:
a. Sector/position on initial radio contact:
1. Identification of aircraft.
2. Identification of ATC unit.
3. Message (if any).
4. The word “over” if required.
b. Subsequent radio transmissions from the same sector/position shall use the same format, except the identification of the ATC unit may be omitted.
TERMINAL. You may omit aircraft identification after initial contact when conducting the final portion of a radar approach.
ABBREVIATED TRANSMISSIONS
Transmissions may be abbreviated as follows:
a. Use the identification prefix and the last 3 digits or letters of the aircraft identification after communications have been established. Do not abbreviate similar sounding aircraft identifications or the identification of an air carrier or other civil aircraft having an FAA authorized call sign.
b. Omit the facility identification after communication has been established.
c. Transmit the message immediately after the callup (without waiting for the aircraft’s reply) when the message is short and receipt is generally assured.
d. Omit the word “over” if the message obviously requires a reply.
INTERPHONE TRANSMISSION PRIORITIES
Give priority to interphone transmissions as follows:
a. First priority. Emergency messages including essential information on aircraft accidents or suspected accidents. After an actual emergency has passed, give a lower priority to messages relating to that accident.
b. Second priority. Clearances and control instructions.
c. Third priority. Movement and control messages using the following order of preference when possible:
1. Progress reports.
2. Departure or arrival reports.
3. Flight plans.
d. Fourth priority. Movement messages on VFR aircraft.
PRIORITY INTERRUPTION
Use the words “emergency” or “control” for interrupting lower priority messages when you have an emergency or control message to transmit.
INTERPHONE MESSAGE FORMAT
Use the following format for interphone intra/interfacility communications:
a. Both the caller and receiver identify their facility and/or position in a manner that insures they will not be confused with another position.
NOTE- Other means of identifying a position, such as substituting departure or arrival gate/fix names for position identification, may be used. However, it must be operationally beneficial, and the procedure fully covered in a letter of agreement or a facility directive, as appropriate.
EXAMPLE- Caller: “Albuquerque Center Sixty Three, Amarillo Departure.”
Receiver: “Albuquerque Center.”
b. Between two facilities which utilize numeric position identification, the caller must identify both facility and position.
EXAMPLE- Caller: “Albuquerque Sixty Three, Fort Worth Eighty Two.”
c. Caller states the type of coordination to be accomplished when advantageous. For example, handoff or APREQ.
d. The caller states the message.
e. The receiver states the response to the caller’s message followed by the receiver’s operating initials.
f. The caller states his or her operating initials.
EXAMPLE-
1. Caller: “Denver High, R Twenty-five.”
Receiver: “Denver High.”
Caller: “Request direct Denver for Northwest Three Twenty-eight.”
Receiver: “Northwest Three Twenty-eight direct Denver approved. H.F.”
Caller: “G.M.”
2. Receiver: “Denver High, Go ahead override.”
Caller: “R Twenty-five, Request direct Denver for Northwest Three Twenty-eight.”
Receiver: “Northwest Three Twenty-eight direct Denver approved. H.F.”
Caller: “G.M.”
3. Caller: (“Bolos” is a departure gate in Houston ARTCC’s Sabine sector)-”Bolos, Houston local.”
Receiver: “Bolos.”
Caller: “Request Flight Level three five zero for American Twenty-five.”
Receiver: “American Twenty-five Flight Level three five zero approved, A.C.”
Caller: “G.M.”
4. Caller: “Sector Twelve, Ontario Approach, APREQ.”
Receiver: “Sector Twelve.”
Caller: “Cactus Five forty-two heading one three zero and climbing to one four thousand.”
Receiver: “Cactus Five forty-two heading one three zero and climbing to one four thousand approved. B.N.”
Caller: “A.M.”
5. Caller: “Zanesville, Columbus, seventy-three line, handoff.”
Receiver: “Zanesville.”
Caller: “Five miles east of Appleton VOR, United Three Sixty-six.”
Receiver: “United Three Sixty-six, radar contact, A.Z.”
Caller: “M.E.”
g. Identify the interphone voice line on which the call is being made when two or more such lines are collocated at the receiving operating position.
EXAMPLE- “Washington Center, Washington Approach on the Fifty Seven line.”
“Chicago Center, O’Hare Tower handoff on the Departure West line.”
h. TERMINAL. The provisions of subparas a, b, c, e, f, g, Interphone Message Termination, may be omitted provided:
1. Abbreviated standard coordination procedures are contained in a facility directive describing the specific conditions and positions that may utilize an abbreviated interphone message format; and
2. There will be no possibility of misunderstanding which positions are using the abbreviated procedures.
INTERPHONE MESSAGE TERMINATION
Terminate interphone messages with your operating initials.
WORDS AND PHRASES
a. Use the words or phrases in radiotelephone and interphone communication as contained in the P/CG or, within areas where Controller Pilot Data Link Communications (CPDLC) is in use, the phraseology contained in the applicable CPDLC message set.
b. The word “heavy” shall be used as part of the identification of heavy jet aircraft as follows:
TERMINAL. In all communications with or about heavy jet aircraft.
EN ROUTE. The use of the word heavy may be omitted except as follows:
1. In communications with a terminal facility about heavy jet operations.
2. In communications with or about heavy jet aircraft with regard to an airport where the en route center is providing approach control service.
3. In communications with or about heavy jet aircraft when the separation from a following aircraft may become less than 5 miles by approved procedure.
4. When issuing traffic advisories.
EXAMPLE- “United Fifty-Eight Heavy.”
NOTE- Most airlines will use the word “heavy” following the company prefix and flight number when establishing communications or when changing frequencies within a terminal facility’s area.
5. When in radio communications with “Air Force One” or “Air Force Two,” do not add the heavy designator to the call sign. State only the call sign “Air Force One/Two” regardless of the type aircraft.
EMPHASIS FOR CLARITY
Emphasize appropriate digits, letters, or similar sounding words to aid in distinguishing between similar sounding aircraft identifications. Additionally:
a. Notify each pilot concerned when communicating with aircraft having similar sounding identifications.
EXAMPLE- “United Thirty-one United, Miami Center, U.S. Air Thirty-one is also on this frequency, acknowledge.”
“U.S. Air Thirty-one U.S. Air, Miami Center, United Thirty-one is also on this frequency, acknowledge.”
b. Notify the operations supervisor-in-charge of any duplicate flight identification numbers or phonetically similar-sounding call signs when the aircraft are operating simultaneously within the same sector.
NOTE- This is especially important when this occurs on a repetitive, rather than an isolated, basis.
WEATHER AND CHAFF SERVICES
a. Issue pertinent information on observed/reported weather and chaff areas. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas.
1. Issue weather and chaff information by defining the area of coverage in terms of azimuth (by referring to the 12-hour clock) and distance from the aircraft or by indicating the general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.
PHRASEOLOGY- WEATHER/CHAFF AREA BETWEEN (number)O’CLOCK AND (number) O’CLOCK (number) MILES, or (number) MILE BAND OF WEATHER/CHAFF FROM (fix or number of miles and direction from fix) TO (fix or number of miles and direction from fix).
2. When a deviation cannot be approved as requested and the situation permits, suggest an alternative course of action.
PHRASEOLOGY- UNABLE DEVIATION (state possible alternate course of action).
FLY HEADING (heading), or PROCEED DIRECT (name of NAVAID).
b. In areas of significant weather, plan ahead and be prepared to suggest, upon pilot request, the use of alternative routes/altitudes.
PHRASEOLOGY- DEVIATION APPROVED, (restrictions if necessary), ADVISE WHEN ABLE TO:
RETURN TO COURSE, or RESUME OWN NAVIGATION, or FLY HEADING (heading), or PROCEED DIRECT (name of NAVAID).
NOTE- Weather significant to the safety of aircraft includes such conditions as funnel cloud activity, lines of thunderstorms, embedded thunderstorms, large hail, wind shear, microbursts, moderate to extreme turbulence (including CAT), and light to severe icing.
c. Inform any tower for which you provide approach control services of observed precipitation on radar which is likely to affect their operations.
d. Use the term “precipitation” when describing radar-derived weather. Issue the precipitation intensity from the lowest descriptor (LIGHT) to the highest descriptor (EXTREME) when that information is available. Do not use the word “turbulence” in describing radar-derived weather.
1. LIGHT.
2. MODERATE.
3. HEAVY.
4. EXTREME.
NOTE- Weather and Radar Processor (WARP) does not display light intensity.
PHRASEOLOGY- (Intensity) PRECIPITATION BETWEEN (number) O’CLOCK AND (number) O’CLOCK, (number) MILES. MOVING (direction) AT (number) KNOTS, TOPS (altitude). PRECIPITATION AREA IS (number) MILES IN DIAMETER.
EXAMPLE- 1. “Extreme precipitation between eleven o’clock and one o’clock, one zero miles moving east at two zero knots, tops flight level three niner zero.” 2. “Heavy precipitation between ten o’clock and two o’clock, one five miles. Precipitation area is two five miles in diameter.” 3. “Heavy to Extreme precipitation between ten o’clock and two o’clock, one five miles. Precipitation area is two five miles in diameter.”
e. When precipitation intensity information is not available.
PHRASEOLOGY- PRECIPITATION BETWEEN (number) O’CLOCK AND (number) O’CLOCK, (number) MILES. MOVING (direction) AT (number) KNOTS, TOPS (altitude), PRECIPITATION AREA IS (number) MILES IN DIAMETER, INTENSITY UNKNOWN.
EXAMPLE- “Precipitation area between one o’clock and three o’clock three five miles. Precipitation area is three zero miles in diameter, intensity unknown.”
NOTE- Phraseology using precipitation intensity descriptions is only applicable when the radar precipitation intensity information is determined by NWS radar equipment or NAS ground based digitized radar equipment with weather capabilities. This precipitation may not reach the surface.
f. EN ROUTE. When issuing Air Route Surveillance Radar (ARSR) precipitation intensity use the following:
1. Describe the lowest displayable precipitation intensity as MODERATE.
2. Describe the highest displayable precipitation intensity as HEAVY to EXTREME.
PHRASEOLOGY- (Intensity) PRECIPITATION BETWEEN (number) O’CLOCK AND (number) O’CLOCK, (number) MILES MOVING (direction) AT (number) KNOTS, TOPS (altitude) PRECIPITATION AREA IS (number) MILES IN DIAMETER.
EXAMPLE- “Moderate precipitation between ten o’clock and one o’clock, three zero miles. Precipitation area is five zero miles in diameter.”
“Moderate to extreme precipitation twelve o’clock and three o’clock, seven zero miles. Precipitation area is one zero zero miles in diameter.”
g. When operational/equipment limitations exist, controllers shall ensure that the highest available level of precipitation intensity within their area of jurisdiction is displayed.
h. The supervisory traffic management coordinator-in-charge/operations supervisor/controller-in-charge shall verify the digitized radar weather information by the best means available (e.g., pilot reports, local tower personnel, etc.) if the weather data displayed by digitized radar is reported as questionable or erroneous. Errors in weather radar presentation shall be reported to the technical operations technician and the air traffic supervisor shall determine if the digitized radar derived weather data is to be displayed and a NOTAM distributed.
NOTE- Anomalous propagation (AP) is a natural occurrence affecting radar and does not in itself constitute a weather circuit failure.
CALM WIND CONDITIONS
TERMINAL. Describe the wind as calm when the wind velocity is less than three knots.
REPORTING WEATHER CONDITIONS
a. When the prevailing visibility at the usual point of observation, or at the tower level, is less than 4 miles, tower personnel shall take prevailing visibility observations and apply the observations as follows:
1. Use the lower of the two observations (tower or surface) for aircraft operations.
2. Forward tower visibility observations to the weather observer.
3. Notify the weather observer when the tower observes the prevailing visibility decrease to less than 4 miles or increase to 4 miles or more.
b. Forward current weather changes to the appropriate control facility as follows:
1. When the official weather changes to a condition which is below 1,000-foot ceiling or below the highest circling minimum, whichever is greater, or less than 3 miles visibility, and when it improves to a condition which is better than those above.
2. Changes which are classified as special weather observations during the time that weather conditions are below 1,000-foot ceiling or the highest circling minimum, whichever is greater, or less than 3 miles visibility.
c. Towers at airports where military turbo-jet en route descents are routinely conducted shall also report the conditions to the ARTCC even if it is not the controlling facility.
d. If the receiving facility informs you that weather reports are not required for a specific time period, discontinue the reports. The time period specified should not exceed the duration of the receiving controller’s tour of duty.
e. EN ROUTE. When you determine that weather reports for an airport will not be required for a specific time period, inform the AFSS/FSS or tower of this determination. The time period specified should not exceed the duration of receiving controller’s tour of duty.
DISSEMINATING WEATHER INFORMATION
TERMINAL. Observed elements of weather information shall be disseminated as follows:
a. General weather information, such as “large breaks in the overcast,” “visibility lowering to the south,” or similar statements which do not include specific values, and any elements derived directly from instruments, pilots, or radar may be transmitted to pilots or other ATC facilities without consulting the weather reporting station.
b. Specific values, such as ceiling and visibility, may be transmitted if obtained by one of the following means:
1. You are properly certificated and acting as official weather observer for the elements being reported.
NOTE- USAF controllers do not serve as official weather observers.
2. You have obtained the information from the official observer for the elements being reported.
3. The weather report was composed or verified by the weather station.
4. The information is obtained from an official Automated Weather Observation System (AWOS) or an Automated Surface Observation System (ASOS).
c. Differences between weather elements observed from the tower and those reported by the weather station shall be reported to the official observer for the element concerned.
Altimeter Settings
CURRENT SETTINGS
a. Current altimeter settings shall be obtained from direct-reading instruments or directly from weather reporting stations.
b. If a pilot requests the altimeter setting in millibars, ask the nearest weather reporting station for the equivalent millibar setting.
c. USAF/USA. Use the term “Estimated Altimeter” for altimeter settings reported or received as estimated.
ALTIMETER SETTING ISSUANCE BELOW LOWEST USABLE FL
a. TERMINAL. Identify the source of an altimeter setting when issued for a location other than the aircraft’s departure or destination airport.
b. EN ROUTE. Identify the source of all altimeter settings when issued.
PHRASEOLOGY- THE (facility name) (time of report if more than one hour old) ALTIMETER (setting).
c. Issue the altimeter setting:
1. To en route aircraft at least one time while operating in your area of jurisdiction. Issue the setting for the nearest reporting station along the aircraft’s route of flight:
2. TERMINAL. To all departures. Unless specifically requested by the pilot, the altimeter setting need not be issued to local aircraft operators who have requested this omission in writing or to scheduled air carriers.
3. TERMINAL. To arriving aircraft on initial contact or as soon as possible thereafter. The tower may omit the altimeter if the aircraft is sequenced or vectored to the airport by the approach control having jurisdiction at that facility.
4. EN ROUTE. For the destination airport to arriving aircraft, approximately 50 miles from the destination, if an approach control facility does not serve the airport.
5. In addition to the altimeter setting provided on initial contact, issue changes in altimeter setting to aircraft executing a nonprecision instrument approach as frequently as practical when the official weather report includes the remarks “pressure falling rapidly.”
d. If the altimeter setting must be obtained by the pilot of an arriving aircraft from another source, instruct the pilot to obtain the altimeter setting from that source.
NOTE- 1. The destination altimeter setting, whether from a local or remote source, is the setting upon which the instrument approach is predicated. 2. Approach charts for many locations specify the source of altimeter settings as non-FAA facilities, such as UNICOMs.
e. When issuing clearance to descend below the lowest usable flight level, advise the pilot of the altimeter setting of the weather reporting station nearest the point the aircraft will descend below that flight level.
f. Department of Defense (DOD) aircraft which operate on “single altimeter settings” (CFR Exemption 2861A) shall be issued altimeter settings in accordance with standard procedures while the aircraft are en route to and from their restricted areas, MOAs, and ATC assigned airspace areas.
g. When the barometric pressure is greater than 31.00 inches Hg., issue the altimeter setting and:
1. En Route/Arrivals. Advise pilots to remain set on altimeter 31.00 until reaching final approach segment.
2. Departures. Advise pilots to set altimeter 31.00 prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower.
PHRASEOLOGY- ALTIMETER, THREE ONE TWO FIVE, SET THREE ONE ZERO ZERO UNTIL REACHING THE FINAL APPROACH FIX. or ALTIMETER, THREE ONE ONE ZERO, SET THREE ONE ZERO ZERO PRIOR TO REACHING ONE THOUSAND THREE HUNDRED.
NOTE- 1. Aircraft with Mode C altitude reporting will be displayed on the controller’s radar scope with a uniform altitude offset above the assigned altitude. With an actual altimeter of 31.28 inches Hg, the Mode C equipped aircraft will show 3,300 feet when assigned 3,000 feet. This will occur unless local directives authorize entering the altimeter setting 31.00 into the computer system regardless of the actual barometric pressure. 2. Flight Standards will implement high barometric pressure procedures by NOTAM defining the geographic area affected. 3. Airports unable to accurately measure barometric pressures above 31.00 inches Hg. will report the barometric pressure as “missing” or “in excess of 31.00 inches of Hg.” Flight operations to or from those airports are restricted to VFR weather conditions.
Runway Visibility Reporting- Terminal
FURNISH RVR/RVV VALUES
Where RVR or RVV equipment is operational, irrespective of subsequent operation or nonoperation of navigational or visual aids for the application of RVR/RVV as a takeoff or landing minima, furnish the values for the runway in use in accordance Terminology.
NOTE- Readout capability of different type/model RVR equipment varies. For example, older equipment minimum readout value is 600 feet. Newer equipment may have minimum readout capability as low as 100 feet. Readout value increments also may differ. Older equipment have minimum readout increments of 200 feet. New equipment increments below 800 feet are 100 feet.
ARRIVAL/DEPARTURE RUNWAY VISIBILITY
a. Issue current touchdown RVR/RVV for the runway(s) in use:
1. When prevailing visibility is 1 mile or less regardless of the value indicated.
2. When RVR/RVV indicates a reportable value regardless of the prevailing visibility.
NOTE- Reportable values are: RVR 6,000 feet or less; RVV 11/2 miles or less.
3. When it is determined from a reliable source that the indicated RVR value differs by more than 400 feet from the actual conditions within the area of the transmissometer, the RVR data is not acceptable and shall not be reported.
NOTE- A reliable source is considered to be a certified weather observer, automated weather observing system, air traffic controller, flight service specialist, or pilot.
4. When the observer has reliable reports, or has otherwise determined that the instrument values are not representative of the associated runway, the data shall not be used.
b. Issue both mid-point and roll-out RVR when the value of either is less than 2,000 feet and the touchdown RVR is greater than the mid-point or roll-out RVR.
c. Local control shall issue the current RVR/RVV to each aircraft prior to landing or departure in accordance with subparas a and b.
TERMINOLOGY
a. Provide RVR/RVV information by stating the runway, the abbreviation RVR/RVV, and the indicated value. When issued along with other weather elements, transmit these values in the normal sequence used for weather reporting.
EXAMPLE- “Runway One Four RVR Two Thousand Four Hundred.”
“Runway Three Two RVV Three Quarters.”
b. When two or more RVR systems serve the runway in use, report the indicated values for the different systems in terms of touchdown, mid, and rollout as appropriate.
EXAMPLE- “Runway Two Two Left RVR Two Thousand, rollout One Thousand Eight Hundred.”
“Runway Two Seven Right RVR One Thousand, mid Eight Hundred, rollout Six Hundred.”
c. When there is a requirement to issue an RVR or RVV value and a visibility condition greater or less than the reportable values of the equipment is indicated, state the condition as “MORE THAN” or “LESS THAN” the appropriate minimum or maximum readable value.
EXAMPLE- “Runway Three Six RVR more than Six Thousand.”
“Runway Niner RVR One Thousand, rollout less than Six Hundred.”
d. When a readout indicates a rapidly varying visibility condition (1,000 feet or more for RVR; one or more reportable values for RVV), report the current value followed by the range of visibility variance.
EXAMPLE- “Runway Two Four RVR Two Thousand, variable One Thousand Six Hundred to Three Thousand.”
“Runway Three One RVV Three-quarters, variable One-quarter to One.”
Automatic Terminal Information Service Procedures
APPLICATION: Use the ATIS, where available, to provide advance noncontrol airport/terminal area and meteorological information to aircraft.
a. Identify each ATIS message by a phonetic letter code word at both the beginning and the end of the message. Automated systems will have the phonetic letter code automatically appended. Exceptions may be made where omissions are required because of special programs or equipment.
1. Each alphabet letter phonetic word shall be used sequentially, except as authorized in subpara a2, beginning with “Alpha,” ending with “Zulu,” and repeated without regard to the beginning of a new day. Identify the first resumed broadcast message with “Alpha” or the first assigned alphabet letter word in the event of a broadcast interruption of more than 12 hours.
2. Specific sequential portions of the alphabet may be assigned between facilities or an arrival and departure ATIS when designated by a letter of agreement or facility directive.
b. The ATIS recording shall be reviewed for completeness, accuracy, speech rate, and proper enunciation before being transmitted.
c. Arrival and departure messages, when broadcast separately, need only contain information appropriate for that operation.
OPERATING PROCEDURES
Maintain an ATIS message that reflects the most current arrival and departure information.
a. Make a new recording when any of the following occur:
1. Upon receipt of any new official weather regardless of whether there is or is not a change in values.
2. When runway braking action reports are received that indicate runway braking is worse than that which is included in the current ATIS broadcast.
3. When there is a change in any other pertinent data, such as runway change, instrument approach in use, new or canceled NOTAMs/PIREPs/HIWAS update, etc.
b. When a pilot acknowledges that he/she has received the ATIS broadcast, controllers may omit those items contained in the broadcasts if they are current. Rapidly changing conditions will be issued by ATC, and the ATIS will contain the following:
EXAMPLE- “Latest ceiling/visibility/altimeter/wind/(other conditions) will be issued by approach control/tower.”
c. Broadcast on all appropriate frequencies to advise aircraft of a change in the ATIS code/message.
d. Controllers shall ensure that pilots receive the most current pertinent information. Ask the pilot to confirm receipt of the current ATIS information if the pilot does not initially state the appropriate ATIS code. Controllers shall ensure that changes to pertinent operational information is provided after the initial confirmation of ATIS information is established. Issue the current weather, runway in use, approach information, and pertinent NOTAMs to pilots who are unable to receive the ATIS.
EXAMPLE- “Verify you have information ALPHA.”
“Information BRAVO now current, visibility three miles.”
“Information CHARLIE now current, Ceiling 1500 Broken.”
“Information CHARLIE now current, advise when you have CHARLIE.”
CONTENT: Include the following in ATIS broadcast as appropriate:
a. Airport/facility name, phonetic letter code, time of weather sequence (UTC). Weather information consisting of wind direction and velocity, visibility, obstructions to vision, present weather, sky condition, temperature, dew point, altimeter, a density altitude advisory when appropriate and other pertinent remarks included in the official weather observation. Wind direction, velocity, and altimeter shall be reported from certified direct reading instruments. Temperature and dew point should be reported from certified direct reading sensors when available. Always include weather observation remarks of lightning, cumulonimbus, and towering cumulus clouds.
NOTE- ASOS/AWOS is to be considered the primary source of wind direction, velocity, and altimeter data for weather observation purposes at those locations that are so equipped. The ASOS Operator Interface Device (OID) displays the magnetic wind as “MAG WND” in the auxiliary data location in the lower left-hand portion of the screen. Other OID displayed winds are true and are not to be used for operational purposes.
b. Man-Portable Air Defense Systems (MANPADS) alert and advisory. Specify the nature and location of threat or incident, whether reported or observed and by whom, time (if known), and notification to pilots to advise ATC if they need to divert.
EXAMPLE- 1. “MANPADS alert. Exercise extreme caution. MANPADS threat reported by TSA, Chicago area.” “Advise on initial contact if you want to divert.” 2. “MANPADS alert. Exercise extreme caution. MANPADS attack observed by tower one-half mile northwest of airfield at one-two-five-zero Zulu.” “Advise on initial contact if you want to divert.”
c. Terminal facilities shall include reported unauthorized laser illumination events on the ATIS broadcast for one hour following the last report. Include the time, location, altitude, color, and direction of the laser as reported by the pilot.
PHRASEOLOGY- UNAUTHORIZED LASER ILLUMINATION EVENT, (UTC time), (location), (altitude), (color), (direction).
EXAMPLE- UNAUTHORIZED LASER ILLUMINATION EVENT, AT 0100z, 8 MILE FINAL RUNWAY 18R AT 3,000 FEET, GREEN LASER FROM THE SOUTHWEST.
d. The ceiling/sky condition, visibility, and obstructions to vision may be omitted if the ceiling is above 5,000 feet and the visibility is more than 5 miles.
EXAMPLE- A remark may be made, “The weather is better than five thousand and five.”
e. Instrument/visual approach/s in use. Specify landing runway/s unless the runway is that to which the instrument approach is made.
f. Departure runway/s (to be given only if different from landing runway/s or in the instance of a “departure only” ATIS).
g. Taxiway closures which affect the entrance or exit of active runways, other closures which impact airport operations, other NOTAMs and PIREPs pertinent to operations in the terminal area. Inform pilots of where hazardous weather is occurring and how the information may be obtained. Include available information of known bird activity.
h. Runway braking action or friction reports when provided. Include the time of the report and a word describing the cause of the runway friction problem.
PHRASEOLOGY- RUNWAY (number) MU (first value, second value, third value) AT (time), (cause).
EXAMPLE- “Runway Two Seven, MU forty-two, forty-one, twenty-eight at one zero one eight Zulu, ice.”
i. Other optional information as local conditions dictate in coordination with ATC. This may include such items as VFR arrival frequencies, temporary airport conditions, LAHSO operations being con-ducted, or other perishable items that may appear only for a matter of hours or a few days on the ATIS message.
j. Low level wind shear/microburst when reported by pilots or is detected on a wind shear detection system.
k. A statement which advises the pilot to read back instructions to hold short of a runway. The air traffic manager may elect to remove this requirement 60 days after implementation provided that removing the statement from the ATIS does not result in increased requests from aircraft for read back of hold short instructions.
l. Instructions for the pilot to acknowledge receipt of the ATIS message by informing the controller on initial contact.
EXAMPLE- “Boston Tower Information Delta. One four zero zero Zulu. Wind two five zero at one zero. Visibility one zero. Ceiling four thousand five hundred broken. Temperature three four. Dew point two eight. Altimeter three zero one zero. ILS-DME Runway Two Seven Approach in use. Departing Runway Two Two Right. Hazardous Weather Information for (geographical area) available on HIWAS, Flight Watch, or Flight Service Frequencies. Advise on initial contact you have Delta.”
Team Position Responsibilities
EN ROUTE SECTOR TEAM POSITION RESPONSIBILITIES
a. En Route Sector Team Concept and Intent:
1. There are no absolute divisions of responsibilities regarding position operations. The tasks to be completed remain the same whether one, two, or three people are working positions within a sector. The team, as a whole, has responsibility for the safe and efficient operation of that sector.
2. The intent of the team concept is not to hold the team accountable for the action of individual members, in the event of an operational accident/incident.
b. Terms. The following terms will be used in en route facilities for the purpose of standardization:
1. Sector. The area of control responsibility (delegated airspace) of the en route sector team, and the team as a whole.
2. Radar Position (R). That position which is in direct communication with the aircraft and which uses radar information as the primary means of separation.
3. Radar Associate (RA). That position sometimes referred to as “D-Side” or “Manual Controller.”
4. Radar Coordinator Position (RC). That position sometimes referred to as “Coordinator,” “Tracker,” or “Handoff Controller” (En Route).
5. Radar Flight Data (FD). That position commonly referred to as “Assistant Controller” or “A-Side” position.
6. Nonradar Position (NR). That position which is usually in direct communication with the aircraft and which uses nonradar procedures as the primary means of separation.
c. Primary responsibilities of the En Route Sector Team Positions:
1. Radar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate automated handoffs.
(e) Assist the radar associate position with nonautomated handoff actions when needed.
(f) Assist the radar associate position in coordination when needed.
(g) Scan radar display. Correlate with flight progress strip information or User Request Evaluation Tool (URET) data, as applicable.
(h) Ensure computer entries are completed on instructions or clearances you issue or receive.
(i) Ensure strip marking and/or URET entries are completed on instructions or clearances you issue or receive.
(j) Adjust equipment at radar position to be usable by all members of the team.
(k) The radar controller shall not be responsible for G/G communications when precluded by VSCS split functionality.
2. Radar Associate Position:
(a) Ensure separation.
(b) At URET facilities, use URET information to plan, organize, and expedite the flow of traffic.
(c) Initiate control instructions.
(d) Operate interphones.
(e) Accept and initiate nonautomated handoffs,
and ensure radar position is made aware of the actions.
(f) Assist the radar position by accepting or initiating automated handoffs which are necessary for the continued smooth operation of the sector, and ensure that the radar position is made immediately aware of any action taken.
(g) Coordinate, including pointouts.
(h) Monitor radios when not performing higher priority duties.
(i) Scan flight progress strips and/or URET data. Correlate with radar data.
(j) Manage flight progress strips and/or URET flight data.
(k) Ensure computer entries are completed on instructions issued or received. Enter instructions issued or received by the radar position when aware of those instructions.
(l) As appropriate, ensure strip marking and/or URET entries are completed on instructions issued or received, and record instructions issued or received by the radar position when aware of them.
(m) Adjust equipment at radar associate position to be usable by all members of the team.
(n) Where authorized, perform URET data entries to keep the activation status of designated URET Airspace Configuration Elements current.
3. Radar Coordinator Position:
(a) Perform interfacility/intrafacility/sector/position coordination of traffic actions.
(b) Advise the radar position and the radar associate position of sector actions required to accomplish overall objectives.
(c) Perform any of the functions of the en route sector team which will assist in meeting situation objectives.
(d) The RC controller shall not be responsible for monitoring or operating radios when precluded by VSCS split functionality.
NOTE- The Radar Position has the responsibility for managing the overall sector operations, including aircraft separation and traffic flows. The Radar Coordinator Position assumes responsibility for managing traffic flows and the Radar Position retains responsibility for aircraft separation when the Radar Coordinator Position is staffed.
4. Radar Flight Data:
(a) Operate interphone.
(b) Assist Radar Associate Position in managing flight progress strips.
(c) Receive/process and distribute flight progress strips.
(d) Ensure flight data processing equipment is operational, except for URET capabilities.
(e) Request/receive and disseminate weather, NOTAMs, NAS status, traffic management, and Special Use Airspace status messages.
(f) Manually prepare flight progress strips when automation systems are not available.
(g) Enter flight data into computer.
(h) Forward flight data via computer.
(i) Assist facility/sector in meeting situation objectives.
5. En Route Nonradar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate transfer of control, communications, and flight data.
(e) Ensure computer entries are completed on instructions or clearances issued or received.
(f) Ensure strip marking is completed on instructions or clearances issued or received.
(g) Facilities utilizing nonradar positions may modify the standards contained in the radar associate, radar coordinator, and radar flight data sections to accommodate facility/sector needs, i.e., nonradar coordinator, nonradar data positions.
TERMINAL RADAR/NONRADAR TEAM POSITION RESPONSIBILITIES
a. Terminal Radar Team Concept and Intent:
1. There are no absolute divisions of responsibilities regarding position operations. The tasks to be completed remain the same whether one, two, or three people are working positions within a facility/sector. The team, as a whole, has responsibility for the safe and efficient operation of that facility/sector.
2. The intent of the team concept is not to hold the team accountable for the action of individual members in the event of an operational error/deviation.
b. Terms. The following terms will be used in terminal facilities for the purposes of standardization.
1. Facility/Sector. The area of control responsibility (delegated airspace) of the radar team, and the team as a whole.
2. Radar Position (R). That position which is in direct communication with the aircraft and which uses radar information as the primary means of separation.
3. Radar Associate Position (RA). That position commonly referred to as “Handoff Controller” or “Radar Data Controller.”
4. Radar Coordinator Position (RC). That position commonly referred to as “Coordinator,” “Tracker,” “Sequencer,” or “Overhead.”
5. Radar Flight Data (FD). That position commonly referred to as “Flight Data.”
6. Nonradar Position (NR). That position which is usually in direct communication with the aircraft and which uses nonradar procedures as the primary means of separation.
c. Primary Responsibilities of the Terminal Radar Team Positions:
1. Radar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate automated handoffs.
(e) Assist the Radar Associate Position with nonautomated handoff actions when needed.
(f) Assist the Radar Associate Position in coordination when needed.
(g) Scan radar display. Correlate with flight progress strip information.
(h) Ensure computer entries are completed on instructions or clearances you issue or receive.
(i) Ensure strip marking is completed on instructions or clearances you issue or receive.
(j) Adjust equipment at Radar Position to be usable by all members of the team.
2. Radar Associate Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Operate interphones.
(d) Maintain awareness of facility/sector activities.
(e) Accept and initiate nonautomated handoffs.
(f) Assist the Radar Position by accepting or initiating automated handoffs which are necessary for the continued smooth operation of the facility/sector and ensure that the Radar Position is made immediately aware of any actions taken.
(g) Coordinate, including point outs.
(h) Scan flight progress strips. Correlate with radar data.
(i) Manage flight progress strips.
(j) Ensure computer entries are completed on instructions issued or received, and enter instructions issued or received by the Radar Position when aware of those instructions.
(k) Ensure strip marking is completed on instructions issued or received, and write instructions issued or received by the Radar Position when aware of them.
(l) Adjust equipment at Radar Associate Position to be usable by all members of the Radar Team.
3. Radar Coordinator Position:
(a) Perform interfacility/sector/position coordination of traffic actions.
(b) Advise the Radar Position and the Radar Associate Position of facility/sector actions required to accomplish overall objectives.
(c) Perform any of the functions of the Radar Team which will assist in meeting situation objectives.
NOTE-The Radar Position has the responsibility of managing the overall sector operations, including aircraft separation and traffic flows. The Radar Coordinator Position assumes responsibility for managing traffic flows and the Radar Position retains responsibility for aircraft separation when the Radar Coordinator Position is staffed.
4. Radar Flight Data:
(a) Operate interphones.
(b) Process and forward flight plan information.
(c) Compile statistical data.
(d) Assist facility/sector in meeting situation objectives.
5. Terminal Nonradar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate transfer of control, communications and flight data.
(e) Ensure computer entries are completed on instructions or clearances issued or received.
(f) Ensure strip marking is completed on instructions or clearances issued or received.
(g) Facilities utilizing nonradar positions may modify the standards contained in the radar associate, radar coordinator, and radar flight data sections to accommodate facility/sector needs, i.e., nonradar coordinator, nonradar data positions.
TOWER TEAM POSITION RESPONSIBILITIES
a. Tower Team Concept and Intent:
1. There are no absolute divisions of responsibilities regarding position operations. The tasks to be completed remain the same whether one, two, or three people are working positions within a tower cab. The team as a whole has responsibility for the safe and efficient operation of that tower cab.
2. The intent of the team concept is not to hold the team accountable for the action of individual members in the event of an operational error/deviation.
b. Terms: The following terms will be used in terminal facilities for the purpose of standardization.
1. Tower Cab: The area of control responsibility (delegated airspace and/or airport surface areas) of the tower team, and the team as a whole.
2. Tower Position(s) (LC or GC): That position which is in direct communications with the aircraft and ensures separation of aircraft in/on the area of jurisdiction.
3. Tower Associate Position(s): That position commonly referred to as “Local Assist,” “Ground Assist,” “Local Associate,” or “Ground Associate.”
4. Tower Cab Coordinator Position (CC): That position commonly referred to as “Coordinator.”
5. Flight Data (FD): That position commonly referred to as “Flight Data.”
6. Clearance Delivery (CD): That position commonly referred to as “Clearance.”
c. Primary responsibilities of the Tower Team Positions:
1. Tower Position(s) (LC or GC):
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate communications equipment.
(d) Utilize tower radar display(s).
(e) Utilize alphanumerics.
(f) Assist the Tower Associate Position with coordination.
(g) Scan tower cab environment.
(h) Ensure computer entries are completed for instructions or clearances issued or received.
(i) Ensure strip marking is completed for instructions or clearances issued or received.
(j) Process and forward flight plan information.
(k) Perform any functions of the Tower Team which will assist in meeting situation objectives.
2. Tower Associate Position(s):
(a) Ensure separation.
(b) Operate interphones.
(c) Maintain awareness of tower cab activities.
(d) Utilize alphanumerics.
(e) Utilize tower radar display(s).
(f) Assist Tower Position by accepting/initiating coordination for the continued smooth operation of the tower cab and ensure that the Tower Position is made immediately aware of any actions taken.
(g) Manage flight plan information.
(h) Ensure computer entries are completed for instructions issued or received and enter instructions issued or received by a Tower Position.
(i) Ensure strip marking is completed for instructions issued or received and enter instructions issued or received by a Tower Position.
3. Tower Coordinator Position:
(a) Perform interfacility/position coordination for traffic actions.
(b) Advise the tower and the Tower Associate Position(s) of tower cab actions required to accomplish overall objectives.
(c) Perform any of the functions of the Tower Team which will assist in meeting situation objectives.
NOTE- The Tower Positions have the responsibility for aircraft separation and traffic flows. The Tower Coordinator Position assumes responsibility for managing traffic flows and the Tower Positions retain responsibility for aircraft separation when the Tower Coordinator Position is staffed.
4. Flight Data:
(a) Operate interphones.
(b) Process and forward flight plan information.
(c) Compile statistical data.
(d) Assist tower cab in meeting situation objectives.
(e) Observe and report weather information.
(f) Utilize alphanumerics.
5. Clearance Delivery:
(a) Operate communications equipment.
(b) Process and forward flight plan information.
(c) Issue clearances and ensure accuracy of pilot read back.
(d) Assist tower cab in meeting situation objectives.
(e) Operate tower equipment.
(f) Utilize alphanumerics.
NOTE-The Tower Positions have the responsibility for aircraft separation and traffic flows. The Tower Coordinator Position assumes responsibility for managing traffic flows and the Tower Positions retain responsibility for aircraft separation when the Tower Coordinator Position is staffed.
12
Airport Traffic Control- Terminal
PROVIDE SERVICE
Provide airport traffic control service based only upon observed or known traffic and airport conditions.
NOTE- When operating in accordance with CFRs, it is the responsibility of the pilot to avoid collision with other aircraft. However, due to the limited space around terminal locations, traffic information can aid pilots in avoiding collision between aircraft operating
within Class B, Class C, or Class D surface areas and the terminal radar service areas, and transiting aircraft operating in proximity to terminal locations.
PREVENTIVE CONTROL
Provide preventive control service only to aircraft operating in accordance with a letter of agreement. When providing this service, issue advice or instructions only if a situation develops which requires corrective action.
NOTE- Preventive control differs from other airport traffic control in that repetitious, routine approval of pilot action is eliminated. Controllers intervene only when they observe a traffic conflict developing.
USE OF ACTIVE RUNWAYS
The local controller has primary responsibility for
operations conducted on the active runway and must control the use of those runways. Positive coordination and control is required as follows:
NOTE- Exceptions may be authorized only as provided in Constraints Governing Supplements and Procedural Deviations, and FAAO JO 7210.3, Facility Operation and Administration, para 10-1-7, Use of Active Runways, where justified by extraordinary circumstances at specific locations.
a. Ground control must obtain approval from local control before authorizing an aircraft or a vehicle to cross or use any portion of an active runway. The coordination shall include the point/intersection at the runway where the operation will occur.
PHRASEOLOGY- CROSS (runway) AT (point/intersection).
b. When the local controller authorizes another controller to cross an active runway, the local controller shall verbally specify the runway to be crossed and the point/intersection at the runway where the operation will occur preceded by the word “cross.”
PHRASEOLOGY- CROSS (runway) AT (point/intersection).
c. The ground controller shall advise the local controller when the coordinated runway operation is complete. This may be accomplished verbally or through visual aids as specified by a facility directive.
d. USA/USAF/USN NOT APPLICABLE. Authorization for aircraft/vehicles to taxi/proceed on or along an active runway, for purposes other than crossing, shall be provided via direct communications on the appropriate local control frequency. This authorization may be provided on the ground control frequency after coordination with local control is completed for those operations specifically described in a facility directive.
NOTE- The USA, USAF, and USN establish local operating procedures in accordance with, respectively, USA, USAF, and USN directives.
e. The local controller shall coordinate with the ground controller before using a runway not previously designated as active.
COORDINATION BETWEEN LOCAL AND GROUND CONTROLLERS
Local and ground controllers shall exchange information as necessary for the safe and efficient use of airport runways and movement areas. This may be accomplished via verbal means, flight progress strips, other written information, or automation displays. As a minimum, provide aircraft identification and applicable runway/intersection/taxiway information as follows:
a. Ground control shall notify local control when a departing aircraft has been taxied to a runway other than one previously designated as active.
b. Ground control must notify local control of any aircraft taxied to an intersection for takeoff. This notification may be accomplished by verbal means or by flight progress strips.
c. When the runways in use for landing/departing aircraft are not visible from the tower or the aircraft using them are not visible on radar, advise the local/ground controller of the aircraft’s location before releasing the aircraft to the other controller.
VEHICLES/EQUIPMENT/PERSONNEL ON RUNWAYS
a. Ensure that the runway to be used is free of all known ground vehicles, equipment, and personnel before a departing aircraft starts takeoff or a landing aircraft crosses the runway threshold.
b. Vehicles, equipment, and personnel in direct communications with the control tower may be authorized to operate up to the edge of an active runway surface when necessary. Provide advisories as specified Traffic Information, Precision Approach Critical Area, as appropriate.
PHRASEOLOGY- PROCEED AS REQUESTED; AND IF NECESSARY, (additional instructions or information).
NOTE- Establishing hold lines/signs is the responsibility of the airport manager. Standards for surface measurements, markings,
and signs are contained in the following Advisory Circulars;
AC 150/5300-13, Airport Design; AC 150/5340-1, Standards for Airport Markings, and AC 150/5340-18, Standards for Airport Sign Systems. The operator is responsible to properly position the aircraft, vehicle, or equipment at the appropriate hold line/sign or designated point. The requirements in, Visually Scanning Runways, remain valid as appropriate.
TRAFFIC INFORMATION
a. Describe vehicles, equipment, or personnel on or near the movement area in a manner which will assist pilots in recognizing them.
EXAMPLE- “Mower left of runway two seven.”
“Trucks crossing approach end of runway two five.”
“Workman on taxiway Bravo.”
“Aircraft left of runway one eight.”
b. Describe the relative position of traffic in an easy to understand manner, such as “to your right” or “ahead of you.”
EXAMPLE- “Traffic, U.S. Air MD-Eighty on downwind leg to your left.”
“King Air inbound from outer marker on straight-in approach to runway one seven.”
c. When using a CTRD, you may issue traffic advisories using the standard radar phraseology prescribed in, Traffic Advisories.
POSITION DETERMINATION : Determine the position of an aircraft before issuing taxi instructions or takeoff clearance.
NOTE- The aircraft’s position may be determined visually by the controller, by pilots, or through the use of the ASDE.
LOW LEVEL WIND SHEAR/MICROBURST ADVISORIES
a. When low level wind shear/microburst is reported by pilots, Integrated Terminal Weather System (ITWS), or detected on wind shear detection systems such as LLWAS NE++, LLWAS-RS, WSP, or TDWR, controllers shall issue the alert to all arriving and departing aircraft. Continue the alert to aircraft until it is broadcast on the ATIS and pilots indicate they have received the appropriate ATIS code. A statement shall be included on the ATIS for 20 minutes following the last report or indication of the wind shear/microburst.
PHRASEOLOGY- LOW LEVEL WIND SHEAR (or MICROBURST, as appropriate) ADVISORIES IN EFFECT.
b. At facilities without ATIS, ensure that wind shear/microburst information is broadcast to all arriving and departing aircraft for 20 minutes following the last report or indication of wind shear/microburst.
1. At locations equipped with LLWAS, the local controller shall provide wind information as follows:
NOTE- The LLWAS is designed to detect low level wind shear conditions around the periphery of an airport. It does not detect wind shear beyond that limitation.
(a) If an alert is received, issue the airport wind and the displayed field boundary wind.
PHRASEOLOGY- WIND SHEAR ALERT. AIRPORT WIND (direction) AT (velocity). (Location of sensor) BOUNDARY WIND (direction) AT (velocity).
(b) If multiple alerts are received, issue an advisory that there are wind shear alerts in two/several/all quadrants. After issuing the advisory, issue the airport wind in accordance with para 3-9-1, Departure Information, followed by the field boundary wind most appropriate to the aircraft operation.
PHRASEOLOGY- WIND SHEAR ALERTS TWO/SEVERAL/ALL QUADRANTS. AIRPORT WIND (direction) AT (velocity). (Location of sensor) BOUNDARY WIND (direction) AT (velocity).
(c) If requested by the pilot, issue specific field boundary wind information even though the LLWAS may not be in alert status.
NOTE- The requirements for issuance of wind information remain valid as appropriate under this paragraph, Departure Information, Landing Information.
2. Wind shear detection systems, including TDWR, WSP, LLWAS NE++ and LLWAS-RS provide the capability of displaying microburst alerts, wind shear alerts, and wind information oriented to the threshold or departure end of a runway. When detected, the associated ribbon display allows the controller to read the displayed alert without any need for interpretation.
(a) If a wind shear or microburst alert is received for the runway in use, issue the alert information for that runway to arriving and departing aircraft as it is displayed on the ribbon display.
PHRASEOLOGY- (Runway) (arrival/departure) WIND SHEAR/MICROBURST ALERT, (windspeed) KNOT GAIN/LOSS, (location).
EXAMPLE- 17A MBA 40K - 3MF
PHRASEOLOGY- RUNWAY 17 ARRIVAL MICROBURST ALERT 40 KNOT LOSS 3 MILE FINAL.
EXAMPLE- 17D WSA 25K+ 2MD
PHRASEOLOGY- RUNWAY 17 DEPARTURE WIND SHEAR ALERT 25 KNOT GAIN 2 MILE DEPARTURE.
(b) If requested by the pilot or deemed appropriate by the controller, issue the displayed wind information oriented to the threshold or departure end of the runway.
PHRASEOLOGY- (Runway) DEPARTURE/THRESHOLD WIND (direction) AT (velocity).
(c) LLWAS NE++ or LLWAS-RS may detect a possible wind shear/microburst at the edge of the system but may be unable to distinguish between a wind shear and a microburst. A wind shear alert message will be displayed, followed by an asterisk, advising of a possible wind shear outside of the system network.
NOTE- LLWAS NE++ when associated with TDWR can detect wind shear/microbursts outside the network if the TDWR fails.
PHRASEOLOGY- (Appropriate wind or alert information) POSSIBLE WIND SHEAR OUTSIDE THE NETWORK.
(d) If unstable conditions produce multiple alerts, issue an advisory of multiple wind shear/microburst alerts followed by specific alert or wind information most appropriate to the aircraft operation.
PHRASEOLOGY- MULTIPLE WIND SHEAR/MICROBURST ALERTS (specific alert or wind information).
(e) The LLWAS NE++ and LLWAS-RS are designed to operate with as many as 50 percent of the total sensors inoperative. When all three remote sensors designated for a specific runway arrival or departure wind display line are inoperative then the LLWAS NE++ and LLWAS-RS for that runway arrival/departure shall be considered out of service. When a specific runway arrival or departure wind display line is inoperative and wind shear/microburst activity is likely; (e.g.; frontal activity, convective storms, PIREPs), a statement shall be included on the ATIS, “WIND SHEAR AND MICROBURST INFORMATION FOR RUNWAY (runway number) ARRIVAL/DEPARTURE NOT AVAILABLE.”
NOTE- The geographic situation display (GSD) is a supervisory planning tool and is not intended to be a primary tool for microburst or wind shear.
USE OF TOWER RADAR DISPLAYS
a. Uncertified tower display workstations shall be used only as an aid to assist controllers in visually locating aircraft or in determining their spacial relationship to known geographical points. Radar services and traffic advisories are not to be provided using uncertified tower display workstations. General information may be given in an easy to understand manner, such as “to your right” or “ahead of you.”
EXAMPLE- “Follow the aircraft ahead of you passing the river at the stacks.” “King Air passing left to right.”
b. Local controllers may use certified tower radar displays for the following purposes:
1. To determine an aircraft’s identification, exact location, or spatial relationship to other aircraft.
NOTE- This authorization does not alter visual separation procedures. When employing visual separation, the provisions of, Visual Separation, apply unless otherwise authorized by the Vice President of Terminal Service.
2. To provide aircraft with radar traffic advisories.
3. To provide a direction or suggested headings to VFR aircraft as a method for radar identification or as an advisory aid to navigation.
PHRASEOLOGY- (Identification), PROCEED (direction)-BOUND, (other instructions or information as necessary), or (identification), SUGGESTED HEADING (degrees), (other instructions as necessary).
NOTE- It is important that the pilot be aware of the fact that the directions or headings being provided are suggestions or are advisory in nature. This is to keep the pilot from being inadvertently misled into assuming that radar vectors (and other associated radar services) are being provided when, in fact, they are not.
4. To provide information and instructions to aircraft operating within the surface area for which the tower has responsibility.
EXAMPLE- “TURN BASE LEG NOW.”
NOTE- Unless otherwise authorized, tower radar displays are intended to be an aid to local controllers in meeting their responsibilities to the aircraft operating on the runways or within the surface area. They are not intended to provide radar benefits to pilots except for those accrued through a more efficient and effective local control position. In addition, local controllers at nonapproach control towers must devote the majority of their time to visually scanning the runways and local area; an assurance of continued positive radar identification could place distracting and operationally inefficient requirements upon the local controller. Therefore, since the requirements of para 5-3-1, Application, cannot be assured, the radar functions prescribed above are not considered to be radar services and pilots should not be advised of being in “radar contact.”
c. Additional functions may be performed provided the procedures have been reviewed and authorized by appropriate management levels.
OBSERVED ABNORMALITIES
When requested by a pilot or when you deem it necessary, inform an aircraft of any observed abnormal aircraft condition.
PHRASEOLOGY- (Item) APPEAR/S (observed condition).
EXAMPLE- “Landing gear appears up.”
“Landing gear appears down and in place.”
“Rear baggage door appears open.”
SURFACE AREA RESTRICTIONS
a. If traffic conditions permit, approve a pilot’s request to cross Class C or Class D surface areas or exceed the Class C or Class D airspace speed limit. Do not, however, approve a speed in excess of 250 knots (288 mph) unless the pilot informs you a higher minimum speed is required.
NOTE- 14 CFR Section 91.117 permits speeds in excess of 250 knots (288 mph) when so required or recommended in the airplane flight manual or required by normal military operating procedures.
b. Do not approve a pilot’s request or ask a pilot to conduct unusual maneuvers within surface areas of Class B, C, or D airspace if they are not essential to the performance of the flight.
EXCEPTION. A pilot’s request to conduct aerobatic practice activities may be approved, when operating in accordance with a letter of agreement, and the activity will have no adverse effect on safety of the air traffic operation or result in a reduction of service to other users.
NOTE- These unusual maneuvers include unnecessary low passes, unscheduled flybys, practice instrument approaches to altitudes below specified minima (unless a landing or
touch-and-go is to be made), or any so-called “buzz jobs”
wherein a flight is conducted at a low altitude and/or a
high rate of speed for thrill purposes. Such maneuvers increase hazards to persons and property and contribute to noise complaints.
VISUALLY SCANNING RUNWAYS
a. Local controllers shall visually scan runways to the maximum extent possible.
b. Ground control shall assist local control in visually scanning runways, especially when runways are in close proximity to other movement areas.
ESTABLISHING TWO-WAY COMMUNICATIONS
Pilots are required to establish two-way radio communications before entering the Class D airspace. If the controller responds to a radio call with, “(a/c call sign) standby,” radio communications have been established and the pilot can enter the Class D
airspace. If workload or traffic conditions prevent immediate provision of Class D services, inform the pilot to remain outside the Class D airspace until conditions permit the services to be provided.
PHRASEOLOGY- (A/c call sign) REMAIN OUTSIDE DELTA AIRSPACE AND STANDBY.
GROUND OPERATIONS WHEN VOLCANIC ASH IS PRESENT
When volcanic ash is present on the airport surface, and to the extent possible:
a. Avoid requiring aircraft to come to a full stop while taxiing.
b. Provide for a rolling takeoff for all departures.
NOTE- When aircraft begin a taxi or takeoff roll on ash contaminated surfaces, large amounts of volcanic ash will again become airborne. This newly airborne ash will significantly reduce visibility and will be ingested by the engines of following aircraft.
Visual Signals
LIGHT SIGNALS : Use ATC light signals control aircraft and the movement of vehicles, equipment, and personnel on the movement area when radio communications cannot be employed.
WARNING SIGNAL : Direct a general warning signal, alternating red and green, to aircraft or vehicle operators, as appropriate, when:
NOTE- The warning signal is not a prohibitive signal and can be followed by any other light signal, as circumstances permit.
a. Aircraft are converging and a collision hazard exists.
b. Mechanical trouble exists of which the pilot might not be aware.
c. Other hazardous conditions are present which call for intensified pilot or operator alertness. These conditions may include obstructions, soft field, ice on the runway, etc.
RECEIVER-ONLY ACKNOWLEDGMENT
To obtain acknowledgment from an aircraft equipped with receiver only, request the aircraft to do the following:
a. Fixed-wing aircraft:
1. Between sunrise and sunset:
(a) Move ailerons or rudders while on the ground.
(b) Rock wings while in flight.
2. Between sunset and sunrise: Flash navigation or landing lights.
b. Helicopters:
1. Between sunrise and sunset:
(a) While hovering, either turn the helicopter toward the controlling facility and flash the landing light or rock the tip path plane.
(b) While in flight, either flash the landing light or rock the tip path plane.
2. Between sunset and sunrise: Flash landing light or search light.
ATC Light Signals
If you observe or are informed of any condition which affects the safe use of a landing area:
NOTE- 1. The airport management/military operations office is responsible for observing and reporting the condition of the landing area. 2. It is the responsibility of the agency operating the airport to provide the tower with current information regarding airport conditions. 3. A disabled aircraft on a runway, after occupants are clear, is normally handled by flight standards and airport management/military operations office personnel in the same manner as any obstruction; e.g., construction equipment.
NOTE- Civil airport managers are required to provide a list of airport employees who are authorized to issue information concerning conditions affecting the safe use of the airport.
EXAMPLE- “DISABLED AIRCRAFT ON RUNWAY.’’
NOTE- 1. Legally, only the airport management/military operations office can close a runway. 2. Military controllers are not authorized to issue NOTAMs. It is the responsibility of the military operations office.
EXAMPLE- “ALL RUNWAYS COVERED BY COMPACTED SNOW SIX INCHES DEEP.”
CLOSED/UNSAFE RUNWAY INFORMATION
If an aircraft requests to takeoff, land, or touch-and-go on a closed or unsafe runway, inform the pilot the runway is closed or unsafe, and
PHRASEOLOGY- RUNWAY (runway number) CLOSED/UNSAFE.
If appropriate, (quote NOTAM information), UNABLE TO ISSUE DEPARTURE/LANDING/TOUCH-AND-GO CLEARANCE. DEPARTURE/LANDING/TOUCH-AND-GO WILL BE AT YOUR OWN RISK.
c. Except as permitted, Side-step Maneuver, where parallel runways are served by separate ILS/MLS systems and one of the runways is closed, the ILS/MLS associated with the closed runway should not be used for approaches unless not using the ILS/MLS would have an adverse impact on the operational efficiency of the airport.
TIMELY INFORMATION: Issue airport condition information necessary for an aircraft’s safe operation in time for it to be useful to the pilot. Include the following, as appropriate:
a. Construction work on or immediately adjacent to the movement area.
b. Rough portions of the movement area.
c. Braking conditions caused by ice, snow, slush, or water.
d. Snowdrifts or piles of snow on or along the edges of the area and the extent of any plowed area.
e. Parked aircraft on the movement area.
f. Irregular operation of part or all of the airport lighting system.
g. Volcanic ash on any airport surface area and whether the ash is wet or dry (if known).
NOTE- Braking action on wet ash may be degraded. Dry ash on the runway may necessitate minimum use of reverse thrust.
h. Other pertinent airport conditions.
BRAKING ACTION
Furnish quality of braking action, as received from pilots or the airport management, to all aircraft as follows:
a. Describe the quality of braking action using the terms “good,” “fair,” “poor,” “nil,” or a combination of these terms. If the pilot or airport management reports braking action in other than the foregoing terms, ask him/her to categorize braking action in these terms.
NOTE- The term “nil” is used to indicate bad or no braking action.
b. Include type of aircraft or vehicle from which the report is received.
EXAMPLE- “Braking action fair to poor, reported by a heavy D-C Ten.”
“Braking action poor, reported by a Boeing Seven Twenty-Seven.”
c. If the braking action report affects only a portion of a runway, obtain enough information from the pilot or airport management to describe the braking action in terms easily understood by the pilot.
EXAMPLE- “Braking action poor first half of runway, reported by a Lockheed Ten Eleven.”
“Braking action poor beyond the intersection of runway two seven, reported by a Boeing Seven Twenty-Seven.”
NOTE- Descriptive terms, such as the first or the last half of the runway, should normally be used rather than landmark descriptions, such as opposite the fire station, south of a taxiway, etc. Landmarks extraneous to the landing runway are difficult to distinguish during low visibility, at night, or anytime a pilot is busy landing an aircraft.
d. Furnish runway friction measurement readings/values as received from airport management to aircraft as follows:
1. Furnish information as received from the airport management to pilots on the ATIS at locations where friction measuring devices, such as MU-Meter, Saab Friction Tester (SFT), and Skiddometer are in use only when the MU values are 40 or less. Use the runway followed by the MU number for each of the three runway segments, time of report, and a word describing the cause of the runway friction problem. Do not issue MU values when all three segments of the runway have values reported greater than 40.
EXAMPLE- “Runway two seven, MU forty-two, forty-one, twenty-eight at one zero one eight Zulu, ice.”
2. Issue the runway surface condition and/or the Runway Condition Reading (RCR), if provided, to all USAF and ANG aircraft. Issue the RCR to other aircraft upon pilot request.
EXAMPLE- “Ice on runway, RCR zero five, patchy.”
NOTE- 1. USAF has established RCR procedures for determining the average deceleration readings of runways under conditions of water, slush, ice, or snow. The use of the RCR code is dependent upon the pilot’s having a “stopping capability chart” specifically applicable to his/her aircraft. 2. USAF offices furnish RCR information at airports serving USAF and ANG aircraft.
BRAKING ACTION ADVISORIES
a. When runway braking action reports are received from pilots or the airport management which include the terms “fair,” “poor,” or “nil” or whenever weather conditions are conducive to deteriorating or rapidly changing runway conditions, include on the ATIS broadcast the statement “Braking Action Advisories are in effect.”
b. During the time Braking Action Advisories are in effect, take the following action:
1. Issue the latest braking action report for the runway in use to each arriving and departing aircraft early enough to be of benefit to the pilot. When possible, include reports from heavy jet aircraft when the arriving or departing aircraft is a heavy jet.
2. If no report has been received for the runway of intended use, issue an advisory to that effect.
PHRASEOLOGY- NO BRAKING ACTION REPORTS RECEIVED FOR RUNWAY (runway number).
3. Advise the airport management that runway braking action reports of “fair,” “poor,” or “nil” have been received.
4. Solicit PIREPs of runway braking action.
c. Include runway friction measurement/values received from airport management on the ATIS. Furnish the information when requested by the pilot in accordance with para 3-3-4, Braking Action.
ARRESTING SYSTEM OPERATION
a. For normal operations, arresting systems remotely controlled by ATC shall remain in the retracted or down position.
NOTE- 1. USN- Runway Arresting Gear- barriers are not operated by ATC personnel. Readiness/rigging of the equipment is the responsibility of the operations department. 2. A request to raise a barrier or hook cable means the barrier or cable on the departure end of the runway. If an approach end engagement is required, the pilot or military authority will specifically request that the approach end cable be raised.
b. Raise aircraft arresting systems whenever:
1. Requested by a pilot.
NOTE- The standard emergency phraseology for a pilot requesting an arresting system to be raised for immediate engagement is: “BARRIER - BARRIER - BARRIER” or “CABLE - CABLE - CABLE.”
2. Requested by military authority; e.g., airfield manager, supervisor of flying, mobile control officer, etc.
NOTE- USAF. Web barriers at the departure end of the runway may remain in the up position when requested by the senior operational commander. The IFR Enroute Supplement and AP-1 will describe specific barrier configuration. ATC will advise transient aircraft of the barrier configuration using the phraseology in subpara c, below.
3. A military jet aircraft is landing with known or suspected radio failure or conditions (drag chute/hydraulic/electrical failure, etc.) that indicate an arresting system may be needed. Exceptions are authorized for military aircraft which cannot engage an arresting system (C-9, C-141, C-5, T-39, etc.) and should be identified in a letter of agreement and/or appropriate military directive.
c. When requested by military authority due to freezing weather conditions or malfunction of the activating mechanism, the barrier/cable may remain in a raised position provided aircraft are advised.
PHRASEOLOGY- YOUR DEPARTURE/LANDING WILL BE TOWARD/OVER A RAISED BARRIER/CABLE ON RUNWAY (number), (location, distance, as appropriate).
d. Inform civil and U.S. Army aircraft whenever rubber supported cables are in place at the approach end of the landing runway, and include the distance of the cables from the threshold. This information may be omitted if it is published in the “Notices to Airmen” publication/DOD FLIP.
EXAMPLE- “Runway One Four arresting cable one thousand feet from threshold.”
e. When arresting system operation has been requested, inform the pilot of the indicated barrier/cable
position.
PHRASEOLOGY- (Identification), BARRIER/CABLE INDICATES UP/DOWN. CLEARED FOR TAKEOFF/TO LAND.
f. Time permitting, advise pilots of the availability of all arresting systems on the runway in question when a pilot requests barrier information.
g. If an aircraft engages a raised barrier/cable, initiate crash alarm procedures immediately.
h. For preplanned practice engagements not associated with emergencies, crash alarm systems need not be activated if, in accordance with local military operating procedures, all required notifications are made before the practice engagement.
FAR FIELD MONITOR (FFM) REMOTE STATUS UNIT
a. Background.
1. To meet the demand for more facilities capable of operating under CAT III weather, Type II equipment is being upgraded to Integrity Level 3. This integrity level will support operations which place a high degree of reliance on ILS guidance for positioning through touchdown.
2. Installation of the FFM remote status indicating units is necessary to attain the integrity necessary to meet internationally agreed upon reliability values in support of CAT III operations on Type II ILS equipment. The remote status indicating unit used in conjunction with Type II equipment adds a third integrity test; thereby, producing an approach aid which has integrity capable of providing Level 3 service.
3. The remote status sensing unit, when installed in the tower cab, will give immediate indications of localizer out-of-tolerance conditions. The alarm in the FFM remote status sensing unit indicates an inoperative or an out-of-tolerance localizer signal; e.g., the
course may have shifted due to equipment
malfunction or vehicle/aircraft encroachment into the critical area.
b. Procedures.
1. Operation of the FFM remote sensing unit will be based on the prevailing weather. The FFM remote sensing unit shall be operational when the weather is below CAT I ILS minimums.
2. When the weather is less than that required for CAT I operations, the GRN-27 FFM remote status sensing unit shall be set at:
(a) “CAT II” when the RVR is less than 2,400 feet.
(b) “CAT III” when the RVR is less than 1,200 feet.
3. When the remote status unit indicates that the localizer FFM is in alarm (aural warning following the preset delay) and:
(a) The aircraft is outside the middle marker (MM), check for encroachment those portions of the critical area that can be seen from the tower. It is understood that the entire critical area may not be visible due to low ceilings and poor visibility. The check is strictly to determine possible causal factors for the out-of-tolerance situation. If the alarm has not cleared prior to the aircraft’s arriving at the MM, immediately issue an advisory that the FFM remote status sensing unit indicates the localizer is unreliable.
(b) The aircraft is between the MM and the inner marker (IM), immediately issue an advisory that the FFM remote status sensing unit indicates the localizer is unreliable.
PHRASEOLOGY- CAUTION, MONITOR INDICATES RUNWAY (number) LOCALIZER UNRELIABLE.
(c) The aircraft has passed the IM, there is no action requirement. Although the FFM has been modified with filters which dampen the effect of false alarms, you may expect alarms when aircraft are located between the FFM and the localizer antenna either on landing or on takeoff.
Airport Lighting
EMERGENCY LIGHTING: Whenever you become
aware that an emergency has or will occur, take action to
provide for the operation of all appropriate airport lighting aids as required.
RUNWAY END IDENTIFIER LIGHTS : When separate on-off controls are provided, operate runway end identifier lights:
a. When the associated runway lights are lighted. Turn the REIL off after:
1. An arriving aircraft has landed.
2. A departing aircraft has left the traffic pattern area.
3. It is determined that the lights are of no further use to the pilot.
b. As required by facility directives to meet local conditions.
c. As requested by the pilot.
HELICOPTER LANDING CLEARANCE
a. Issue landing clearance for helicopters to movement areas other than active runways, or from diverse directions to points on active runways, with additional instructions, as necessary. Whenever possible, issue landing clearance in lieu of extended hover-taxi or air-taxi operations.
PHRASEOLOGY- MAKE APPROACH STRAIGHT-IN/CIRCLING LEFT/RIGHT TURN TO (location, runway, taxiway, helipad, Maltese cross) ARRIVAL/ARRIVAL ROUTE (number, name, or code).
HOLD SHORT OF (active runway, extended runway centerline, other).
REMAIN (direction/distance; e.g., 700 feet, 1 1/2 miles) FROM (runway, runway centerline, other helicopter/aircraft).
CAUTION (power lines, unlighted obstructions, wake turbulence, etc.).
CLEARED TO LAND.
CONTACT GROUND.
AIR TAXI TO RAMP.
b. If landing is requested to nonmovement areas and, in your judgment, the operation appears to be reasonable, use the following phraseology instead of the landing clearance in subpara a above.
PHRASEOLOGY- PROCEED AS REQUESTED, USE CAUTION (reason and additional instructions, as appropriate).
c. If landing is requested to an area not visible, an area not authorized for helicopter use, an unlighted nonmovement area at night, or an area off the airport, and traffic is not a factor, use the following phraseology.
PHRASEOLOGY- LANDING AT (requested location) WILL BE AT YOUR OWN RISK (reason and additional instructions, as necessary).
TRAFFIC (as applicable), or TRAFFIC NOT A FACTOR.
d. Unless requested by the pilot, do not issue downwind landings if the tailwind exceeds 5 knots.
NOTE- A pilot request to land at a given point from a given direction constitutes such a request.
Sea Lane Operations
APPLICATION : Where sea lanes are established and controlled, apply the provisions of this section.
DEPARTURE SEPARATION : Separate a departing aircraft from a preceding departing or arriving aircraft using the same sea lane by ensuring that it does not commence takeoff until:
a. The other aircraft has departed and crossed the end of the sea lane or turned to avert any conflict. If you can determine distances by reference to suitable landmarks, the other aircraft need only be airborne if the following minimum distance exists between aircraft:
1. When only Category I aircraft are involved- 1,500 feet.
2. When a Category I aircraft is preceded by a Category II aircraft- 3,000 feet.
3. When either the succeeding or both are Category II aircraft- 3,000 feet.
4. When either is a Category III aircraft- 6,000 feet.
b. A preceding landing aircraft has taxied out of the sea lane.
NOTE- Due to the absence of braking capability, caution should be exercised when instructing a float plane to hold a position as the aircraft will continue to move because of prop generated thrust. Clearance to taxi into position and hold should, therefore, be followed by takeoff or other clearance as soon as practicable.
ARRIVAL SEPARATION
Separate an arriving aircraft from another aircraft using
the same sea lane by ensuring that the arriving aircraft does not cross the landing threshold until one of the following conditions exists:
a. The other aircraft has landed and taxied out of the sea lane. Between sunrise and sunset, if you can determine distances by reference to suitable landmarks and the other aircraft has landed, it need not be clear of the sea lane if the following minimum distance from the landing threshold exists:
1. When a Category I aircraft is landing behind a Category I or II- 2,000 feet.
2. When a Category II aircraft is landing behind a Category I or II- 2,500 feet.
b. The other aircraft has departed and crossed the end of the sea lane or turned to avert any conflict. If you can determine distances by reference to suitable landmarks and the other aircraft is airborne, it need not have crossed the end of the sea lane if the following minimum distance from the landing threshold exists:
1. When only Category I aircraft are involved- 1,500 feet.
2. When either is a Category II aircraft- 3,000 feet.
3. When either is a Category III aircraft- 6,000 feet.
electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
flight data processing. This plots an aircraft’s expected position as calculated by computer from the aircraft flight plan (stored electronically by the Australian Advanced Air Traffic System).
frequency. A measure of how frequently an electromagnetic wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA).
Global Positioning System. The Global Positioning System (GPS) is a collection of 24 earth-orbiting satellites which allows any person who owns a GPS receiver to determine their location on the planet. More information on the Global Positioning System can be found How a GPS receiver works (How Stuff Works, USA) and The Global Positioning System: The role of atomic clocks (Beyond Discovery, National Academy of Sciences, USA).
radar. The use of reflected radio waves to determine the location of an object and its speed if it is moving. It is an acronym derived from radio detecting and ranging. For more information see How radar works (How Stuff Works, USA).
radio frequency. This is lowest of the electromagnetic radiation frequencies. Radio frequencies, or radio waves, have wavelengths ranging from less than a centimetre to as long as 100 kilometres. (See also electromagnetic radiation).
We divide the radio wave part of the electromagnetic spectrum into bands that are allocated to different uses. These include AM (amplitude modulation), FM (frequency modulation) and CB (citizens’ band) radio, television, aircraft communications, satellites, mobile phones and pagers. Within each band, no two transmissions can use the same part of the spectrum – or frequency - at the same time. For this reason, each band within the radio wave spectrum, itself a part of the broader electromagnetic spectrum, must be managed carefully to ensure the best use of this limited resource. For more information see How the radio spectrum works (How Stuff Works, USA).
VHF (very high frequency) radio. Radios that use frequencies in the range 30 to 300 megahertz (millions of oscillations per second). The wave length of these VHF radio waves range from 1 metre to 10 metres.
As used in this manual, the following abbreviations have the meanings indicated.
FAA Order JO 7110.65 Abbreviations
Abbreviation Meaning
AAR Airport acceptance rate
AC Advisory Circular
ACC Area Control Center
ACD ARTS Color Display
ACE-IDS ASOS Controller Equipment- Information Display System
ACL Aircraft list
ACLS Automatic Carrier Landing System
ADC Aerospace Defense Command
ADIZ Air Defense Identification Zone (to be pronounced “AY DIZ”)
ADS Automatic Dependent Surveillance
ADS-B Automatic Dependent Surveillance Broadcast
ADS-C Automatic Dependent Surveillance Contract
AFP Airspace Flow Program
AFSS Automated Flight Service Station
AIDC ATS Interfacility Data Communications
AIM Aeronautical Information Manual
AIRMET Airmen’s meteorological information
ALERFA Alert phase code (Alerting Service)
ALNOT Alert notice
ALS Approach Light System
ALTRV Altitude reservation
AMASS Airport Movement Area Safety System
AMB Ambiguity-A disparity greater than 2 miles exists between the position declared for a target by ATTS and another facility’s computer declared position during interfacility handoff
AMVER Automated Mutual Assistance Vessel Rescue System
ANG Air National Guard
APR ATC preferred route
APREQ Approval Request
ARINC Aeronautical Radio Incorporated
ARIP Air refueling initial point
ARSR Air route surveillance radar
ARTCC Air Route Traffic Control Center
ARTS Automated Radar Terminal System
ASD Aircraft Situation Display
ASDE Airport surface detection equipment
ASDE-X Airport Surface Detection Equipment System - Model X
ASF Airport Stream Filters
ASOS Automated Surface Observing System
ASR Airport surveillance radar
ATC Air traffic control
ATCAA ATC assigned airspace
ATCSCC David J. Hurley Air Traffic Control System Command Center
ATD Along-Track Distance
ATIS Automatic Terminal Information Service
ATO Air Traffic Organization
ATO COO Air Traffic Organization Chief Operating Officer
ATS Air Traffic Service
AWOS Automated Weather Observing System
BASE Cloud base
CA Conflict Alert
CARCAH Chief, Aerial Reconnaissance Coordination, All Hurricanes
CARF Central Altitude Reservation Function
CARTS Common ARTS
CAT Clear air turbulence
CDT Controlled departure time
CENRAP Center Radar ARTS Presentation
CEP Central East Pacific
CERAP Combined Center/RAPCON
CFR Code of Federal Regulations
CIC Controller-in-Charge
CNS Continuous
CPDLC Controller Pilot Data Link Communications
CPME Calibration Performance Monitor Equipment
CTA Control Area
CTRD Certified Tower Radar Display
CVFP Charted Visual Flight Procedure
CWA Center Weather Advisory
DARC Direct Access Radar Channel
DETRESFA Distress Phase code (Alerting Service)
DF Direction finder
DH Decision height
DL Departure List
DME Distance measuring equipment compatible with TACAN
DOE Department of Energy
DP Instrument Departure Procedure
DR Dead reckoning
DRT Diversion recovery tool
DSR Display System Replacement
DTAS Digital Terminal Automation Systems
DTM Digital Terrain Map
DVFR Defense Visual Flight Rules
DVRSN Diversion
EA Electronic Attack
EAS En Route Automation System
EDCT Expect Departure Clearance Time
EFC Expect further clearance
ELP Emergency Landing Pattern
ELT Emergency locator transmitter
EOS End Service
EOVM Emergency obstruction video map
ERIDS En Route Information Display System
ETA Estimated time of arrival
ETMS Enhanced Traffic Management System
FAA Federal Aviation Administration
FAAO FAA Order
FANS Future Air Navigation System
FDIO Flight Data Input/Output
FDP Flight data processing
FIR Flight Information Region
FL Flight level
FLIP Flight Information Publication
FLM Front-Line Manager
FLY Fly or flying
FMS Flight Management System
FMSP Flight Management System Procedure
FSM Flight Schedule Monitor
FSS Flight Service Station
GCA Ground controlled approach
GNSS Global Navigation Satellite System
GPD Graphics Plan Display
GPS Global Positioning System
GS Ground stop
HAR High Altitude Redesign
HERT Host Embedded Route Text
HF/RO High Frequency/Radio Operator
HIRL High intensity runway lights
IAFDOF Inappropriate Altitude for Direction of Flight
ICAO International Civil Aviation Organization
IDENT Aircraft identification
IDS Information Display System
IFR Instrument flight rules
IFSS International Flight Service Station
ILS Instrument Landing System
INCERFA Uncertainty Phase code (Alerting Service)
INREQ Information request
INS Inertial Navigation System
IR IFR military training route
IRU Inertial Reference Unit
ITWS Integrated Terminal Weather System
JATO Jet assisted takeoff
LAHSO Land and Hold Short Operations
LOA Letter of Agreement
LLWAS Low Level Wind Shear Alert System
LLWAS NE Low Level Wind Shear Alert System Network Expansion
LLWAS-RS Low Level Wind Shear Alert System Relocation/Sustainment
LLWS Low Level Wind Shear
L/MF Low/medium frequency
LORAN Long Range Navigation System
Mach Mach number
MALS Medium Intensity Approach Light System
MALSR Medium Approach Light System with runway alignment indicator lights
MAP Missed approach point
MARSA Military authority assumes responsibility for separation of aircraft
MCA Minimum crossing altitude
MCI Mode C Intruder
MDA Minimum descent altitude
MDM Main display monitor
MEA Minimum en route (IFR) altitude
MEARTS Micro En Route Automated Radar Tracking System
METAR Aviation Routine Weather Report
MIA Minimum IFR altitude
MIAWS Medium Intensity Airport Weather System
MIRL Medium intensity runway lights
MLS Microwave Landing System
MNPS Minimum Navigation Performance Specification
MNT Mach Number Technique
MOA Military operations area
MOCA Minimum obstruction clearance altitude
MRA Minimum reception altitude
MSAW Minimum Safe Altitude Warning
MSL Mean sea level
MTI Moving target indicator
MTR Military training route
MVA Minimum vectoring altitude
NADIN National Airspace Data Interchange Network
NAR National Automation Request
NAS National Airspace System
NAT ICAO North Atlantic Region
NBCAP National Beacon Code Allocation Plan
NDB Nondirectional radio beacon
NHOP National Hurricane Operations Plan
NIDS National Institute for Discovery Sciences
NM Nautical mile
NOAA National Oceanic and Atmospheric Administration
NOPAC North Pacific
NORAD North American Aerospace Defense Command
NOS National Ocean Service
NOTAM Notice to Airmen
NRP North American Route Program
NRR Nonrestrictive Route
NRS Navigation Reference System
NTZ No transgression zone
NWS National Weather Service
NWSOP National Winter Storm Operations Plan
ODALS Omnidirectional Approach Lighting System
ODP Obstacle Departure Procedure
OID Operator Interface Device
ONER Oceanic Navigational Error Report
OS Operations Supervisor
OTR Oceanic transition route
PAPI Precision Approach Path Indicators
PAR Precision approach radar
PAR Preferred arrival route
PBCT Proposed boundary crossing time
P/CG Pilot/Controller Glossary
PDAR Preferential departure arrival route
PDC Pre-Departure Clearance
PDR Preferential departure route
PIDP Programmable indicator data processor
PPI Plan position indicator
PTP Point-to-point
PVD Plan view display
RA Radar Associate
RAIL Runway alignment indicator lights
RAPCON Radar Approach Control Facility (USAF)
RATCF Radar Air Traffic Control Facility (USN)
RBS Radar bomb scoring
RCC Rescue Coordination Center
RCLS Runway Centerline System
RCR Runway condition reading
RDP Radar data processing
RE Recent (used to qualify weather phenomena such as rain, e.g. recent rain = RERA)
REIL Runway end identifier lights
RNAV Area navigation
RNP Required Navigation Performance
RTQC Real-Time Quality Control
RVR Runway visual range
RVSM Reduced Vertical Separation Minimum
RVV Runway visibility value
SAA Special Activity Airspace
SAR Search and rescue
SATCOM Satellite Communication
SELCAL Selective Calling System
SFA Single frequency approach
SFO Simulated flameout
SID Standard Instrument Departure
SIGMET Significant meteorological information
SPA Special Posting Area
SPECI Nonroutine (Special) Aviation Weather Report
STAR Standard terminal arrival
STARS Standard Terminal Automation Replacement System
STMC Supervisory Traffic Management Coordinator
STMCIC Supervisory Traffic Management Coordinator-in-charge
STOL Short takeoff and landing
SURPIC Surface Picture
SVFR Special Visual Flight Rules
TAA Terminal arrival area
TAS Terminal Automation Systems
TACAN TACAN UHF navigational aid (omnidirectional course and distance information)
TAWS Terrain Awareness Warning System
TCAS Traffic Alert and Collision Avoidance System
TCDD Tower cab digital display
TDLS Terminal Data Link System
TDW Tower display workstation
TDWR Terminal Doppler Weather Radar
TDZL Touchdown Zone Light System
TMC Traffic Management Coordinator
TMU Traffic Management Unit
TRACON Terminal Radar Approach Control
TRSA Terminal radar service area
UFO Unidentified flying object
UHF Ultra high frequency
URET User request evaluation tool
USA United States Army
USAF United States Air Force
USN United States Navy
UTC Coordinated universal time
UTM Unsuccessful transmission message
UUA Urgent pilot weather report
VFR Visual flight rules
VHF Very high frequency
VMC Visual meteorological conditions
VNAV Vertical Navigation
VOR VHF navigational aid (omnidirectional course information)
VOR/DME Collocated VOR and DME navigational aids (VHF course and UHF distance information)
VORTAC Collocated VOR and TACAN navigation aids (VHF and UHF course and UHF distance information)
VR VFR military training route
VSCS Voice Switching and Control System
WAAS Wide Area Augmentation System
WARP Weather and Radar Processing
WATRS West Atlantic Route System
WSO Weather Service Office
WSP Weather System Processor
WST Convective SIGMET
If an aircraft declares a state of “minimum fuel,” inform any facility to whom control jurisdiction is transferred of the minimum fuel problem and be alert for any occurrence which might delay the aircraft en route.
NOTE- Use of the term “minimum fuel” indicates recognition by a pilot that his/her fuel supply has reached a state where, upon reaching destination, he/she cannot accept any undue delay. This is not an emergency situation but merely an advisory that indicates an emergency situation is possible should any undue delay occur. A minimum fuel advisory does not imply a need for traffic priority. Common sense and good judgment will determine the extent of assistance to be given in minimum fuel situations. If, at any time, the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, the pilot should declare an emergency and report fuel remaining in minutes.
REPORTING ESSENTIAL FLIGHT INFORMATION
Report as soon as possible to the appropriate AFSS/FSS, airport manager’s office, ARTCC, approach control facility, operations office, or military operations office any information concerning components of the NAS or any flight conditions which may have an adverse effect on air safety.
NOTE- AFSSs/FSSs are responsible for classifying and disseminating Notices to Airmen.
NAVAID MALFUNCTIONS
a. When an aircraft reports a ground-based NAVAID malfunction, take the following actions:
1. Request a report from a second aircraft.
2. If the second aircraft reports normal operations, continue use and inform the first aircraft. Record the incident on FAA Form 7230-4 or appropriate military form.
3. If the second aircraft confirms the malfunction or in the absence of a second aircraft report, activate the standby equipment or request the monitor facility to activate.
4. If normal operation is reported after the standby equipment is activated, continue use, record the incident on FAA Form 7230-4 or appropriate military form, and notify technical operations personnel (the Systems Engineer of the ARTCC when an en route aid is involved).
5. If continued malfunction is reported after the standby equipment is activated or the standby equipment cannot be activated, inform technical operations personnel and request advice on whether or not the aid should be shut down. In the absence of a second aircraft report, advise the technical operations personnel of the time of the initial aircraft report and the estimated time a second aircraft report could be obtained.
b. When an aircraft reports a GPS anomaly, request the following information and/or take the following actions:
1. Record the following minimum information:
(a) Aircraft call sign and type.
(b) Location.
(c) Altitude.
(d) Date/time of occurrence.
2. Record the incident on FAA Form 7230-4 or appropriate military form.
3. Broadcast the anomaly report to other aircraft as necessary.
PHRASEOLOGY- ATTENTION ALL AIRCRAFT, GPS REPORTED UNRELIABLE IN VICINITY/AREA (position).
EXAMPLE- “Attention all aircraft, GPS reported unreliable in the area 30 miles south of Waco VOR.”
c. When an aircraft reports a Wide Area Augmentation System (WAAS) anomaly, request the following information and/or take the following actions:
1. Determine if the pilot has lost all WAAS service.
PHRASEOLOGY- ARE YOU RECEIVING ANY WAAS SERVICE?
2. If the pilot reports receipt of any WAAS service, acknowledge the report and continue normal operations.
3. If the pilot reports loss of all WAAS service, report as a GPS anomaly using procedures in subpara 2-1-10b.
USE OF MARSA
a. MARSA may only be applied to military operations specified in a letter of agreement or other appropriate FAA or military document.
NOTE- Application of MARSA is a military command prerogative. It will not be invoked indiscriminately by individual units or pilots. It will be used only for IFR operations requiring its use. Commands authorizing MARSA will ensure that its implementation and terms of use are documented and coordinated with the control agency having jurisdiction over the area in which the operations are conducted. Terms of use will assign responsibility and provide for separation among participating aircraft.
b. ATC facilities do not invoke or deny MARSA. Their sole responsibility concerning the use of MARSA is to provide separation between military aircraft engaged in MARSA operations and other nonparticipating IFR aircraft.
c. DOD shall ensure that military pilots requesting special-use airspace/ATCAAs have coordinated with the scheduling agency, have obtained approval for entry, and are familiar with the appropriate MARSA procedures. ATC is not responsible for determining which military aircraft are authorized to enter special-use airspace/ATCAAs.
MILITARY PROCEDURES
Military procedures in the form of additions, modifications, and exceptions to the basic FAA procedure are prescribed herein when a common procedure has not been attained or to fulfill a specific requirement. They shall be applied by:
a. ATC facilities operated by that military service.
EXAMPLE- 1. An Air Force facility providing service for an Air Force base would apply USAF procedures to all traffic regardless of class. 2. A Navy facility providing service for a Naval Air Station would apply USN procedures to all traffic regardless of class.
b. ATC facilities, regardless of their parent organization (FAA, USAF, USN, USA), supporting a designated military airport exclusively. This designation determines which military procedures are to be applied.
EXAMPLE- 1. An FAA facility supports a USAF base exclusively; USAF procedures are applied to all traffic at that base. 2. An FAA facility provides approach control service for a Naval Air Station as well as supporting a civil airport; basic FAA procedures are applied at both locations by the FAA facility. 3. A USAF facility supports a USAF base and provides approach control service to a satellite civilian airport; USAF procedures are applied at both locations by the USAF facility.
c. Other ATC facilities when specified in a letter of agreement.
EXAMPLE- A USAF unit is using a civil airport supported by an FAA facility- USAF procedures will be applied as specified in a letter of agreement between the unit and the FAA facility to the aircraft of the USAF unit. Basic FAA procedures will be applied to all other aircraft.
FORMATION FLIGHTS
a. Control formation flights as a single aircraft. When individual control is requested, issue advisory information which will assist the pilots in attaining separation. When pilot reports indicate separation has been established, issue control instructions as required.
NOTE- 1. Separation responsibility between aircraft within the formation during transition to individual control rests with the pilots concerned until standard separation has been attained. 2. Formation join-up and breakaway will be conducted in VFR weather conditions unless prior authorization has been obtained from ATC or individual control has been approved.
b. Military and civil formation flights in RVSM airspace.
1. Utilize RVSM separation standards for a formation flight, which consists of all RVSM approved aircraft.
2. Utilize non-RVSM separation standards for a formation flight above FL 290, which does not consist of all RVSM approved aircraft.
3. If aircraft are requesting to form a formation flight to FL 290 or above, the controller who issues the clearance creating the formation flight is responsible for ensuring that the proper equipment suffix is entered for the lead aircraft.
4. If the flight departs as a formation, and is requesting FL 290 or above, the first center sector shall ensure that the proper equipment suffix is entered.
5. If the formation flight is below FL 290 and later requests FL 290 or above, the controller receiving the RVSM altitude request shall ensure the proper equipment suffix is entered.
6. Upon break-up of the formation flight, the controller initiating the break-up shall ensure that all aircraft or flights are assigned their proper equipment suffix.
COORDINATE USE OF AIRSPACE
a. Ensure that the necessary coordination has been accomplished before you allow an aircraft under
your control to enter another controller’s area of jurisdiction.
b. Before you issue control instructions directly or relay through another source to an aircraft which is within another controller’s area of jurisdiction that will change that aircraft’s heading, route, speed, or altitude, ensure that coordination has been accomplished with each of the controllers listed below whose area of jurisdiction is affected by those instructions unless otherwise specified by a letter of agreement or a facility directive:
1. The controller within whose area of jurisdiction the control instructions will be issued.
2. The controller receiving the transfer of control.
3. Any intervening controller(s) through whose area of jurisdiction the aircraft will pass.
c. If you issue control instructions to an aircraft through a source other than another controller (e.g., ARINC, AFSS/FSS, another pilot) ensure that the necessary coordination has been accomplished with any controllers listed in subparas b1, 2, and 3, whose area of jurisdiction is affected by those instructions unless otherwise specified by a letter of agreement or a facility directive.
CONTROL TRANSFER
a. Transfer control of an aircraft in accordance with the following conditions:
1. At a prescribed or coordinated location, time, fix, or altitude; or,
2. At the time a radar handoff and frequency change to the receiving controller have been completed and when authorized by a facility directive or letter of agreement which specifies the type and extent of control that is transferred.
b. Transfer control of an aircraft only after eliminating any potential conflict with other aircraft for which you have separation responsibility.
c. Assume control of an aircraft only after it is in your area of jurisdiction unless specifically coordinated or as specified by letter of agreement or a facility directive.
SURFACE AREAS
a. Coordinate with the appropriate nonapproach control tower on an individual aircraft basis before issuing a clearance which would require flight within a surface area for which the tower has responsibility unless otherwise specified in a letter of agreement.
b. Coordinate with the appropriate control tower for transit authorization when you are providing radar traffic advisory service to an aircraft that will enter another facility’s airspace.
NOTE- The pilot is not expected to obtain his/her own authorization through each area when in contact with a radar facility.
c. Transfer communications to the appropriate facility, if required, prior to operation within a surface area for which the tower has responsibility.
RADIO COMMUNICATIONS TRANSFER
a. Transfer radio communications before an aircraft enters the receiving controller’s area of jurisdiction unless otherwise coordinated or specified by a letter of agreement or a facility directive.
b. Transfer radio communications by specifying the
following:
NOTE- Radio communications transfer procedures may be specified by a letter of agreement or contained in the route description of an MTR as published in the DOD Planning AP/1B (AP/3).
1. The facility name or location name and terminal function to be contacted. TERMINAL: Omit the location name when transferring communications to another controller within your facility; except when instructing the aircraft to change frequency for final approach guidance include the name of the facility.
2. Frequency to use except the following may be omitted:
(a) FSS frequency.
(b) Departure frequency if previously given or published on a SID chart for the procedure issued.
(c) TERMINAL: (1) Ground or local control frequency if in your opinion the pilot knows which frequency is in use. (2) The numbers preceding the decimal point if the ground control frequency is in the 121 MHz bandwidth.
EXAMPLE-
“Contact Tower.”
“Contact Ground.”
“Contact Ground Point Seven.”
“Contact Ground, One Two Zero Point Eight.”
“Contact Huntington Radio.”
“Contact Departure.”
“Contact Los Angeles Center, One Two Three Point Four.”
3. Time, fix, altitude, or specifically when to contact a facility. You may omit this when compliance is expected upon receipt.
NOTE- AIM, para 5-3-1, ARTCC Communications, informs pilots that they are expected to maintain a listening watch on the transferring controller’s frequency until the time, fix, or altitude specified.
PHRASEOLOGY- CONTACT (facility name or location name and terminal function), (frequency). If required, AT (time, fix, or altitude).
c. In situations where an operational advantage will be gained, and following coordination with the receiving controller, you may instruct aircraft on the ground to monitor the receiving controller’s frequency.
EXAMPLE-
“Monitor Tower.”
“Monitor Ground.”
“Monitor Ground Point Seven.”
“Monitor Ground, One Two Zero Point Eight.”
d. In situations where a sector has multiple frequencies or when sectors are combined using multiple frequencies and the aircraft will remain under your jurisdiction, transfer radio communication by specifying the following:
PHRASEOLOGY- (Identification) CHANGE TO MY FREQUENCY (state frequency).
EXAMPLE- “United two twenty-two change to my frequency one two three point four.”
e. Avoid issuing a frequency change to helicopters known to be single-piloted during air-taxiing, hovering, or low-level flight. Whenever possible, relay necessary control instructions until the pilot is able to change frequency.
NOTE- Most light helicopters are flown by one pilot and require the constant use of both hands and feet to maintain control. Although Flight Control Friction Devices assist the pilot, changing frequency near the ground could result in inadvertent ground contact and consequent loss of control. Pilots are expected to advise ATC of their single-pilot status if unable to comply with a frequency change.
f. In situations where the controller does not want the pilot to change frequency but the pilot is expecting or may want a frequency change, use the following phraseology.
PHRASEOLOGY- REMAIN THIS FREQUENCY.
OPERATIONAL REQUESTS Respond to a request from another controller, a pilot or vehicle operator by one of the following verbal means:
a. Restate the request in complete or abbreviated terms followed by the word “APPROVED.” The phraseology “APPROVED AS REQUESTED” may be substituted in lieu of a lengthy readback.
PHRASEOLOGY- (Requested operation) APPROVED. or APPROVED AS REQUESTED.
b. State restrictions followed by the word “APPROVED.”
PHRASEOLOGY- (Restriction and/or additional instructions, requested operation) APPROVED.
c. State the word “UNABLE” and, time permitting, a reason.
PHRASEOLOGY- UNABLE (requested operation). and when necessary, (reason and/or additional instructions.)
d. State the words “STAND BY.”
NOTE- “STAND BY” is not an approval or denial. The controller acknowledges the request and will respond at a later time.
WAKE TURBULENCE
a. Apply wake turbulence procedures to aircraft operating behind heavy jets/B757s and, where indicated, to small aircraft behind large aircraft.
NOTE- Para 5-5-4, Minima, specifies increased radar separation for small type aircraft landing behind large, heavy, or B757 aircraft because of the possible effects of wake turbulence.
b. The separation minima shall continue to touchdown for all IFR aircraft not making a visual approach or maintaining visual separation.
WAKE TURBULENCE CAUTIONARY ADVISORIES
a. Issue wake turbulence cautionary advisories and the position, altitude if known, and direction of flight of the heavy jet or B757 to:
1. TERMINAL. VFR aircraft not being radar vectored but are behind heavy jets or B757s.
2. IFR aircraft that accept a visual approach or visual separation.
3. TERMINAL. VFR arriving aircraft that have previously been radar vectored and the vectoring has been discontinued.
b. Issue cautionary information to any aircraft if in your opinion, wake turbulence may have an adverse effect on it. When traffic is known to be a heavy aircraft, include the word heavy in the description.
NOTE- Wake turbulence may be encountered by aircraft in flight as well as when operating on the airport movement area. Because wake turbulence is unpredictable, the controller is not responsible for anticipating its existence or effect. Although not mandatory during ground operations, controllers may use the words jet blast, propwash, or rotorwash, in lieu of wake turbulence, when issuing a caution advisory.
PHRASEOLOGY-CAUTION WAKE TURBULENCE (traffic information).
TRAFFIC ADVISORIES
Unless an aircraft is operating within Class A airspace or omission is requested by the pilot, issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima. Where no separation minima applies, such as for VFR aircraft outside of Class B/Class C airspace, or a TRSA, issue traffic advisories to those aircraft on your frequency when in your judgment their proximity warrants it. Provide this service as follows:
a. To radar identified aircraft:
1. Azimuth from aircraft in terms of the 12-hour clock, or
2. When rapidly maneuvering aircraft prevent accurate issuance of traffic as in 1 above, specify the direction from an aircraft’s position in terms of the eight cardinal compass points (N, NE, E, SE, S, SW, W, and NW). This method shall be terminated at the pilot’s request.
3. Distance from aircraft in miles.
4. Direction in which traffic is proceeding and/or relative movement of traffic.
NOTE- Relative movement includes closing, converging, parallel same direction, opposite direction, diverging, overtaking, crossing left to right, crossing right to left.
5. If known, type of aircraft and altitude.
PHRASEOLOGY- TRAFFIC, (number) O’CLOCK, or when appropriate, (direction) (number) MILES, (direction)-BOUND and/or (relative movement), and if known, (type of aircraft and altitude). or When appropriate, (type of aircraft and relative position), (number of feet) FEET ABOVE/BELOW YOU. If altitude is unknown, ALTITUDE UNKNOWN.
EXAMPLE- “Traffic, eleven o’clock, one zero miles, southbound, converging, Boeing Seven Twenty Seven, one seven thousand.” “Traffic, twelve o’clock, one five miles, opposite direction, altitude unknown.” “Traffic, ten o’clock, one two miles, southeast bound, one thousand feet below you.”
6. When requested by the pilot, issue radar vectors to assist in avoiding the traffic, provided the aircraft to be vectored is within your area of jurisdiction or coordination has been effected with the sector/facility in whose area the aircraft is operating.
7. If unable to provide vector service, inform the pilot.
8. Inform the pilot of the following when traffic you have issued is not reported in sight:
(a) The traffic is no factor.
(b) The traffic is no longer depicted on radar.
PHRASEOLOGY-TRAFFIC NO FACTOR/NO LONGER OBSERVED, or (number) O’CLOCK TRAFFIC NO FACTOR/NO LONGER OBSERVED, or (direction) TRAFFIC NO FACTOR/NO LONGER OBSERVED.
b. To aircraft that are not radar identified:
1. Distance and direction from fix.
2. Direction in which traffic is proceeding.
3. If known, type of aircraft and altitude.
4. ETA over the fix the aircraft is approaching, if appropriate.
PHRASEOLOGY- TRAFFIC, (number) MILES/MINUTES (direction) OF (airport or fix), (direction)-BOUND, and if known, (type of aircraft and altitude), ESTIMATED (fix) (time), or TRAFFIC, NUMEROUS AIRCRAFT VICINITY (location). If altitude is unknown, ALTITUDE UNKNOWN.
EXAMPLE- “Traffic, one zero miles east of Forsythe V-O-R, Southbound, M-D Eighty, descending to one six thousand.”
“Traffic, reported one zero miles west of Downey V-O-R, northbound, Apache, altitude unknown, estimated Joliet V-O-R one three one five.”
“Traffic, eight minutes west of Chicago Heights V-O-R, westbound, Mooney, eight thousand, estimated Joliet V-O-R two zero three five.”
“Traffic, numerous aircraft, vicinity of Delia airport.”
c. For aircraft displaying Mode C, not radar identified, issue indicated altitude.
EXAMPLE- “Traffic, one o’clock, six miles, eastbound, altitude indicates six thousand five hundred.”
BIRD ACTIVITY INFORMATION
a. Issue advisory information on pilot-reported, tower-observed, or radar-observed and pilot-verified bird activity. Include position, species or size of birds, if known, course of flight, and altitude. Do this for at least 15 minutes after receipt of such information from pilots or from adjacent facilities unless visual observation or subsequent reports reveal the activity is no longer a factor.
EXAMPLE- “Flock of geese, one o’clock, seven miles, northbound, last reported at four thousand.”
“Flock of small birds, southbound along Mohawk River, last reported at three thousand.”
“Numerous flocks of ducks, vicinity Lake Winnebago, altitude unknown.”
b. Relay bird activity information to adjacent facilities and to AFSSs/FSSs whenever it appears it will become a factor in their areas.
TRANSFER OF POSITION RESPONSIBILITY
The transfer of position responsibility shall be accomplished in accordance with the “Standard Operating Practice (SOP) for the Transfer of Position Responsibility,” and appropriate facility directives each time operational responsibility for a position is transferred from one specialist to another.
WHEELS DOWN CHECK
USA/USAF/USN : Remind aircraft to check wheels down on each approach unless the pilot has previously reported wheels down for that approach.
NOTE- The intent is solely to remind the pilot to lower the wheels, not to place responsibility on the controller.
a. Tower shall issue the wheels down check at an appropriate place in the pattern.
PHRASEOLOGY- CHECK WHEELS DOWN.
b. Approach/arrival control, GCA shall issue the wheels down check as follows:
1. To aircraft conducting ASR, PAR, or radar monitored approaches, before the aircraft starts descent on final approach.
2. To aircraft conducting instrument approaches
and remaining on the radar facility’s frequency, before the aircraft passes the outer marker/final approach fix.
PHRASEOLOGY- WHEELS SHOULD BE DOWN.
SUPERVISORY NOTIFICATION
Ensure supervisor/controller-in-charge (CIC) is aware of conditions which impact sector/position operations including, but not limited to, the following:
a. Weather.
b. Equipment status.
c. Potential sector overload.
d. Emergency situations.
e. Special flights/operations.
PILOT DEVIATION NOTIFICATION
When it appears that the actions of a pilot constitute a pilot deviation, notify the pilot, workload permitting.
PHRASEOLOGY- (Identification) POSSIBLE PILOT DEVIATION ADVISE YOU CONTACT (facility) AT (telephone number).
TCAS RESOLUTION ADVISORIES
a. When an aircraft under your control jurisdiction informs you that it is responding to a TCAS Resolution Advisory (RA), do not issue control instructions that are contrary to the RA procedure that a crew member has advised you that they are executing. Provide safety alerts regarding terrain or obstructions and traffic advisories for the aircraft responding to the RA and all other aircraft under your control jurisdiction, as appropriate.
b. Unless advised by other aircraft that they are also responding to a TCAS RA, do not assume that other aircraft in the proximity of the responding aircraft are involved in the RA maneuver or are aware of the responding aircraft’s intended maneuvers. Continue to provide control instructions, safety alerts, and traffic advisories as appropriate to such aircraft.
c. Once the responding aircraft has begun a maneuver in response to an RA, the controller is not responsible for providing standard separation between the aircraft that is responding to an RA and any other aircraft, airspace, terrain or obstructions. Responsibility for standard separation resumes when one of the following conditions are met:
1. The responding aircraft has returned to its assigned altitude, or
2. A crew member informs you that the TCAS maneuver is completed and you observe that standard separation has been reestablished, or
3. The responding aircraft has executed an alternate clearance and you observe that standard separation has been reestablished.
NOTE- 1. AC 120-55A, Air Carrier Operational Approval and Use of TCAS II, suggests pilots use the following phraseology to notify controllers during TCAS events. When a TCAS RA may affect an ATC clearance, inform ATC when beginning the maneuver, or as soon as workload permits.
EXAMPLE- 1. “New York Center, United 321, TCAS climb.”
NOTE- 2. When the RA has been resolved, the flight crew should advise ATC they are returning to their previously assigned clearance or subsequent amended clearance.
EXAMPLE- 2. “New York Center, United 321, clear of conflict, returning to assigned altitude.”
RVSM OPERATIONS
Controller responsibilities shall include but not be limited to the following:
a. Non-RVSM aircraft operating in RVSM airspace.
1. Ensure non-RVSM aircraft are not permitted in RVSM airspace unless they meet the criteria of excepted aircraft and are previously approved by the operations supervisor/controller-in-charge (CIC). The following aircraft are excepted: DOD, Lifeguard, manufacturer aircraft being flown for development/certification, and Foreign State aircraft. These exceptions are accommodated on a workload or traffic-permitting basis.
NOTE- The operations supervisor/CIC is responsible for system acceptance of a non-RVSM aircraft beyond the initial sector to sector coordination following the pilot request to access the airspace. Operations supervisor/CIC responsibilities are defined in FAA Order 7210.3, Chapter 6, Section 9, Reduced Vertical Separation Minimum (RVSM).
2. A non-RVSM exception designated by the DOD for special consideration via the DOD Priority Mission website shall be referred to as a STORM flight.
3. Ensure sector-to-sector coordination for all non-RVSM aircraft operations within RVSM airspace.
4. Inform the operational supervisor/CIC when a non-RVSM exception flight is denied clearance into RVSM airspace or is removed from RVSM airspace.
b. Non-RVSM aircraft transitioning RVSM airspace.
Ensure that operations supervisors/CICs are made aware when non-RVSM aircraft are transitioning through RVSM airspace.
c. Apply appropriate separation standards and remove any aircraft from RVSM airspace that advises it is unable RVSM due to equipment while en route.
d. Use “negative RVSM” in all verbal ground-to-ground communications involving non-RVSM aircraft while cleared to operate within RVSM airspace.
EXAMPLE- “Point out Baxter21 climbing to FL 360, negative RVSM.”
e. For the following situations, use the associated phraseology:
1. To deny clearance into RVSM airspace.
PHRASEOLOGY- “UNABLE CLEARANCE INTO RVSM AIRSPACE.”
2. To request a pilot to report when able to resume RVSM.
PHRASEOLOGY- “REPORT ABLE TO RESUME RVSM.”
f. In the event of a change to an aircraft’s navigational capability amend the equipment suffix in order to properly identify non-RVSM aircraft on the controller display.
TERRAIN AWARENESS WARNING SYSTEM (TAWS) ALERTS
a. When an aircraft under your control jurisdiction informs you that it is responding to a TAWS (or other on-board low altitude) alert, do not issue control instructions that are contrary to the TAWS procedure that a crew member has advised you that they are executing. Provide safety alerts regarding terrain or obstructions and traffic advisories for the aircraft responding to the TAWS alert and all other aircraft under your control jurisdiction, as appropriate.
b. Once the responding aircraft has begun a maneuver in response to TAWS alert, the controller is not responsible for providing standard separation between the aircraft that is responding to a TAWS alert and any other aircraft, airspace, terrain or obstructions. Responsibility for standard separation resumes when one of the following conditions are met:
1. The responding aircraft has returned to its assigned altitude, or
2. A crew member informs you that the TAWS maneuver is completed and you observe that standard separation has been reestablished, or
3. The responding aircraft has executed an alternate clearance and you observe that standard separation has been reestablished.
Flight Plans and Control Information
RECORDING INFORMATION
a. Record flight plan information required by the type of flight plan and existing circumstances. Use authorized abbreviations when possible.
NOTE- Generally, all military overseas flights are required to clear through a specified military base operations office (BASOPS). Pilots normally will not file flight plans directly with an FAA facility unless a BASOPS is not available. BASOPS will, in turn, forward the IFR flight notification message to the appropriate center.
b. EN ROUTE. When flight plans are filed directly with the center, record all items given by the pilot either on a flight progress strip/flight data entry or on a voice recorder. If the latter, enter in box 26 of the initial flight progress strip the sector or position number to identify where the information may be found in the event search and rescue (SAR) activities become necessary.
FORWARDING INFORMATION
a. Except during EAS FDP operation, forward the flight plan information to the appropriate ATC facility, AFSS/FSS, or BASOPS and record the time of filing and delivery on the form.
b. EN ROUTE. During EAS FDP operation, the above manual actions are required in cases where the data is not forwarded automatically by the computer.
NOTE- During EAS FDP operation, data is exchanged between interfaced automated facilities and both the data and time of transmission are recorded automatically.
c. EN ROUTE. Forward proposed tower en route flight plans and any related amendments to the appropriate departure terminal facility.
FORWARDING VFR DATA
TERMINAL : Forward aircraft departure times to AFSSs/FSSs or military operations offices when they have requested them. Forward other VFR flight plan data only if requested by the pilot.
MILITARY DVFR DEPARTURES
TERMINAL : Forward departure times on all military DVFR departures from joint-use airports to the military operations office.
NOTE- 1. Details for handling air carrier, nonscheduled civil, and military DVFR flight data are contained in FAAO JO 7610.4, Special Operations. 2. Military pilots departing DVFR from a joint-use airport will include the phrase “DVFR to (destination)” in their initial call-up to an FAA operated tower.
IFR TO VFR FLIGHT PLAN CHANGE
Request a pilot to contact the appropriate AFSS/FSS if the pilot informs you of a desire to change from an IFR to a VFR flight plan.
IFR FLIGHT PROGRESS DATA
Forward control information from controller to controller within a facility, then to the receiving facility as the aircraft progresses along its route. Where appropriate, use computer equipment in lieu of manual coordination procedures. Do not use the remarks section of flight progress strips in lieu of voice coordination to pass control information. Ensure that flight plan and control information is correct and up-to-date. When covered by a letter of agreement/facility directive, the time requirements of subpara a may be reduced, and the time requirements of subpara b1 and para 2-2-11, Forwarding Amended and UTM Data, subpara a may be increased up to 15 minutes when facilitated by automated systems or mandatory radar handoffs; or if operationally necessary because of manual data processing or nonradar operations, the time requirements of subpara a may be increased.
NOTE- 1. The procedures for preparing flight plan and control information related to altitude reservations (ALTRVs) are contained in FAAO JO 7210.3, para 8-1-2, Facility Operation and Administration, ALTRV Flight Data Processing. Development of the methods for assuring the accuracy and completeness of ALTRV flight plan and control information is the responsibility of the military liaison and security officer. 2. The term facility in this paragraph refers to centers and terminal facilities when operating in an en route capacity.
a. Forward the following information at least 15 minutes before the aircraft is estimated to enter the receiving facility’s area:
1. Aircraft identification.
2. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
3. Assigned altitude and ETA over last reporting point/fix in transferring facility’s area or assumed departure time when the departure point is the last point/fix in the transferring facility’s area.
4. Altitude at which aircraft will enter the receiving facility’s area if other than the assigned altitude.
5. True airspeed.
6. Point of departure.
7. Route of flight remaining.
8. Destination airport and clearance limit if other than destination airport.
9. ETA at destination airport (not required for military or scheduled air carrier aircraft).
10. Altitude requested by the aircraft if assigned altitude differs from requested altitude (within a facility only).
NOTE- When an aircraft has crossed one facility’s area and assignment at a different altitude is still desired, the pilot will reinitiate the request with the next facility.
11. When flight plan data must be forwarded manually and an aircraft has been assigned a beacon code by the computer, include the code as part of the flight plan.
NOTE- When an IFR aircraft, or a VFR aircraft that has been assigned a beacon code by the EAS and whose flight plan will terminate in another facility’s area, cancels ATC service or does not activate the flight plan, send a remove strips (RS) message on that aircraft via the EAS keyboard, the FDIO keyboard or call via service F.
12. Longitudinal separation being used between aircraft at the same altitude if it results in these aircraft having less than 10 minutes separation at the facilities’ boundary.
13. Any additional nonroutine operational information pertinent to flight safety.
NOTE- EN ROUTE. This includes alerting the receiving controller that the flight is conducting celestial navigation training.
b. Forward position report over last reporting point in the transferring facility’s area if any of the following conditions exist:
1. Time differs more than 3 minutes from estimate given.
2. Requested by receiving facility.
3. Agreed to between facilities.
MANUAL INPUT OF COMPUTER-ASSIGNED BEACON CODES
When a flight plan is manually entered into the computer and a computer-assigned beacon code has been forwarded with the flight plan data, insert the beacon code in the appropriate field as part of the input message.
ALTRV INFORMATION
EN ROUTE : When an aircraft is a part of an approved ALTRV, forward only those items necessary to properly identify the flight, update flight data contained in the ALTRV APVL, or revise previously given information.
COMPUTER MESSAGE VERIFICATION
EN ROUTE : Unless your facility is equipped to automatically obtain acknowledgment of receipt of transferred data, when you transfer control information by computer message, obtain, via Service F, acknowledgment that the receiving center has received the message and verification of the following:
a. Within the time limits specified by a letter of agreement or when not covered by a letter of agreement, at least 15 minutes before the aircraft is estimated to enter the receiving facility’s area, or at the time of a radar handoff, or coordination for transfer of control:
1. Aircraft identification.
2. Assigned altitude.
3. Departure or coordination fix time.
b. Any cancellation of IFR or EAS generated VFR flight plan.
TRANSMIT PROPOSED FLIGHT PLAN
EN ROUTE
a. Transmit proposed flight plans which fall within an ARTCC’s Proposed Boundary Crossing Time (PBCT) parameter to adjacent ARTCC’s via the Computer B network during hours of inter-center computer operation. In addition, when the route of flight of any proposed flight plan exceeds 20 elements external to the originating ARTCC’s area, NADIN shall be used to forward the data to all affected centers.
b. During nonautomated operation, the proposed flight plans shall be sent via NADIN to the other centers involved when any of the following conditions are met:
1. The route of flight external to the originating center’s area consists of 10 or more elements and the flight will enter 3 or more other center areas.
NOTE- An element is defined as either a fix or route as specified in FAAO JO 7110.10, Flight Services, para 6-3-3, IFR Flight Plan Control Messages.
2. The route of flight beyond the first point of exit from the originating center’s area consists of 10 or more elements, which are primarily fixes described in fix-radial-distance or latitude/longitude format, regardless of the number of other center areas entered.
3. The flight plan remarks are too lengthy for interphone transmission.
FORWARDING AMENDED AND UTM DATA
a. Forward any amending data concerning previously forwarded flight plans except that revisions to ETA information in para 2-2-6, IFR Flight Progress Data, need only be forwarded when the time differs by more than 3 minutes from the estimate given.
PHRASEOLOGY- (Identification), REVISED (revised information).
EXAMPLE- “American Two, revised flight level, three three zero.”
“United Eight Ten, revised estimate, Front Royal two zero zero five.”
“Douglas Five Zero One Romeo, revised altitude, eight thousand.”
“U.S. Air Eleven Fifty-one, revised type, heavy Boeing Seven Sixty-seven.”
b. Computer acceptance of an appropriate input message fulfills the requirement for sending amended data. During EAS FDP operations, the amendment data are considered acknowledged on receipt of a computer update message or a computer-generated flight progress strip containing the amended data.
NOTE- 1. The successful utilization of automation equipment requires timely and accurate insertion of changes and/or new data. 2. If a pilot is not issued a computer-generated PDR/PDAR/PAR and if amendment data is not entered into the computer, the next controller will have incorrect route information.
c. Forward any amended control information and record the action on the appropriate flight progress strip. Additionally, when a route or altitude in a previously issued clearance is amended within 15 minutes of an aircraft’s proposed departure time, the facility that amended the clearance shall coordinate the amendment with the receiving facility via verbal AND automated means to ensure timely passage of the information.
NOTE- The term “receiving” facility means the ATC facility that is expected to transmit the amended clearance to the intended aircraft/pilot.
d. EN ROUTE. Effect manual coordination on any interfacility flight plan data that is not passed through automated means.
AIRBORNE MILITARY FLIGHTS
Forward to AFSSs/FSSs the following information received from airborne military aircraft:
a. IFR flight plans and changes from VFR to IFR flight plans.
b. Changes to an IFR flight plan as follows:
1. Change in destination:
(a) Aircraft identification and type.
(b) Departure point.
(c) Original destination.
(d) Position and time.
(e) New destination.
(f) ETA.
(g) Remarks including change in fuel exhaustion time.
(h) Revised ETA.
2. Change in fuel exhaustion time.
NOTE- This makes current information available to AFSSs/FSSs for relay to military bases concerned and for use by centers in the event of two-way radio communications failure.
FORWARDING FLIGHT PLAN DATA BETWEEN U.S. ARTCCs AND CANADIAN ACCs
EN ROUTE
a. Domestic. (Continental U.S./Canadian airspace except Alaska) Proposed departure flight plans and en route estimates will be handled on a 30 minute lead time (or as bilaterally agreed) between any ACC and ARTCC.
b. International. Any route changes (except SIDs) must be forwarded to the appropriate Oceanic/Pre-oceanic ACC or ARTCC with an optimum lead time of 30 minutes or as soon as this information becomes available.
c. Initially, if a flight goes from U.S. airspace into Canadian airspace and returns to U.S. airspace, the ACC will be responsible for forwarding the flight plan data to the appropriate ARTCC by voice transmission except for flights which traverse mutually agreed on airways/fixes. These airways/fixes will be determined on a case-by-case basis and will be based on time and distance considerations at the service area office.
TELETYPE FLIGHT DATA FORMAT- U.S. ARTCCs - CANADIAN ACCs
EN ROUTE : The exchange of flight plan data between Canadian ACCs and U.S. ARTCCs shall be made as follows:
a. The U.S. ARTCCs will transmit flight data to the Canadian ACCs in one of the following formats:
1. NADIN II input format as described in the NAS Management Directives (MDs) for:
(a) Flight Plan Messages: (1) Active. (2) Proposed.
(b) Amendment messages.
(c) Cancellation messages.
(d) Response Messages to Canadian Input:
(1) Acknowledgment messages. (2) Error messages. (3) Rejection messages.
2. Transport Canada (TC) ACC Flight Strip Format: Where the data to be printed on the ACC strip form exceeds the strip form field size, the NADIN II input format in 1 above will be used. Input sequentially fields 1 through 8 in para 2-2-6, IFR Flight Progress Data, subpara a.
b. TC’s ACCs will transmit flight data to the FAA ARTCCs in the following format:
1. NADIN II input format as described in NAS MDs for:
(a) Flight Plan Messages: (1) Active. (2) Proposed.
(b) Amendment messages.
(c) Cancellation messages.
(d) Correction messages.
NORTH AMERICAN ROUTE PROGRAM (NRP) INFORMATION
a. “NRP” shall be retained in the remarks section of the flight plan if the aircraft is moved due to weather, traffic, or other tactical reasons.
NOTE- Every effort should be made to ensure the aircraft is returned to the original filed flight plan/altitude as soon as conditions warrant.
b. If the route of flight is altered due to a pilot request, “NRP” shall be removed from the remarks section of the flight plan.
c. “NRP” shall not be entered in the remarks section of a flight plan, unless prior coordination is accomplished with the ATCSCC or as prescribed by international NRP flight operations procedures.
d. The en route facility within which an international flight entering the conterminous U.S. requests to participate in the NRP shall enter “NRP” in the remarks section of the flight plan.
Flight Progress Strips
GENERAL - Unless otherwise authorized in a facility directive, use flight progress strips to post current data on air traffic and clearances required for control and other air traffic control services. To prevent misinterpretation when data is hand printed, use standard hand-printed characters.
En route: Flight progress strips shall be posted.
a. Maintain only necessary current data and remove the strips from the flight progress boards when no longer required for control purposes. To correct, update, or preplan information:
1. Do not erase or overwrite any item. Use an “X” to delete a climb/descend and maintain arrow, an at or above/below symbol, a cruise symbol, and unwanted altitude information. Write the new altitude information immediately adjacent to it and within the same space.
2. Do not draw a horizontal line through an altitude being vacated until after the aircraft has reported or is observed (valid Mode C) leaving the altitude.
3. Preplanning may be accomplished in red pencil.
b. Manually prepared strips shall conform to the format of machine-generated strips and manual strip preparation procedures will be modified simultaneously with the operational implementation of changes in the machine-generated format.
c. Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e. 5,000 feet as 5, and 2,800 as 2.8.
NOTE- A slant line crossing through the number zero and underline of the letter “s” on handwritten portions of flight progress strips are required only when there is reason to believe the lack of these markings could lead to misunderstanding. A slant line crossing through the number zero is required on all weather data.
EN ROUTE DATA ENTRIES
a. Information recorded on the flight progress strips (FAA Forms 7230-19) shall be entered in the correspondingly numbered spaces:
Block Information Recorded
1. Verification symbol if required.
2. Revision number.DSR-Not used.
3. Aircraft identification.
4. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
5. Filed true airspeed.
6. Sector number.
7. Computer identification number if required.
8. Estimated ground speed.
9. Revised ground speed or strip request (SR) originator.
10. Strip number.DSR- Strip number/Revision number.
11. Previous fix.
12. Estimated time over previous fix.
13. Revised estimated time over previous fix.
14. Actual time over previous fix, or actual departure time entered on first fix posting after departure.
14a. Plus time expressed in minutes from the previous fix to the posted fix.
15. Center-estimated time over fix (in hours and minutes), or clearance information for departing aircraft.
16. Arrows to indicate if aircraft is departing (‘!) or arriving (“!).
17. Pilot-estimated time over fix.
18. Actual time over fix, time leaving holding fix, arrival time at nonapproach control airport, or symbol indicating cancellation of IFR flight plan for arriving aircraft, or departure time (actual or assumed).
19. Fix. For departing aircraft, add proposed departure time.
20. Altitude information (in hundreds of feet) or as noted below.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e. FL 330 as 33, 5,000 feet as 5, and 2,800 as 2.8.
20a. OPTIONAL USE, when voice recorders are operational;REQUIRED USE, when the voice recorders are not operating and strips are being use at the facility. This space is used to record reported RA events. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
21. Next posted fix or coordination fix.
22. Pilot’s estimated time over next fix.
23. Arrows to indicate north (‘!), south (“!), east (’!), or west (!) direction of flight if required.
24. Requested altitude.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e., FL 330 as 33, 5,000 feet as 5, and 2,800 as 2.8.
25. Point of origin, route as required for control and data relay, and destination.
26. Pertinent remarks, minimum fuel, point out/radar vector/speed adjustment information or sector/position number (when applicable in accordance with para 2-2-1, Recording Information), or NRP. High Altitude Redesign (HAR) or Point-to-point (PTP) may be used at facilities actively using these programs.
27. Mode 3/A beacon code if applicable.
28. Miscellaneous control data (expected further clearance time, time cleared for approach, etc.).
29-30. Transfer of control data and coordination indicators.
b. Latitude/longitude coordinates may be used to define waypoints and may be substituted for nonadapted NAVAIDs in space 25 of domestic en route flight progress strips provided it is necessary to accommodate a random RNAV or GNSS route request.
c. Facility air traffic managers may authorize the optional use of spaces 13, 14, 14a, 22, 23, 24, and 28 for point out information, radar vector information, speed adjustment information, or transfer of control data.
OCEANIC DATA ENTRIES
a. The Ocean21 system displays information on electronic flight progress strips and, in the event of a catastrophic system failure, will print flight progress strips with data in the corresponding numbered spaces:
Block Information Recorded
1. Mode 3/A beacon code, if applicable.
2. Number of aircraft, if more than one, and type of aircraft.
3. Aircraft identification.
4. Reduced separation flags. Indicators are available for:
M - Mach Number Technique (MNT), R - Reduced MNT,D or 3 - Distance-based longitudinal separation using 50 NM (D) or 30 NM (3), andW- Reduced Vertical Separation Minimum (RVSM).These flags are selectable for aircraft whose flight plans contain the required equipment qualifiers for each separation criteria.
5. Controlling sector number.
6. Filed airspeed or assigned Mach number/True airspeed.
7. Reported flight level. May contain an indicator for a flight that is climbing (‘!) or descending (“!). Reports from Mode C, ADS or position reports are displayed in that order of preference.
8. Cleared flight level. May contain an indicator for a future conditional altitude ( * ) that cannot be displayed.
9. Requested flight level, if applicable.
10. Previously reported position.
11. Actual time over previously reported position.
12. Last reported position.
13. Actual time over last reported position.
14. Next reporting position.
15. In-conformance pilot’s estimate or controller-accepted pilot’s estimate for next reporting position.
16. Future reporting position(s).
17. System estimate for future reporting position(s).
18. Departure airport or point of origin.
19. Destination airport or filed point of flight termination.
20. Indicators. Indicators and toggles for displaying or suppressing the display of the route of flight (F), second flight profile (2), radar contact (A), annotations (&), degraded Required Navigation Performance (RNP, indicator R) and clearance restrictions (X).
21. Coordination indicator(s).
22. Annotations.
23. Clearance restrictions and conditions (may be multiple lines).
24. Strip number and total number of strips (printed strips only).
b. Standard annotations and abbreviations for Field 22 may be specified by facility directives.
TERMINAL DATA ENTRIES
a. Arrivals: Information recorded on the flight progress strips (FAA Forms 7230-7.1, 7230-7.2, and 7230-8) shall be entered in the correspondingly numbered spaces. Facility managers can authorize omissions and/or optional use of spaces 2A, 8A, 8B, 9A, 9B, 9C, and 10-18, if no misunderstanding will result. These omissions and/or optional uses shall be specified in a facility directive.
Block Information Recorded
1. Aircraft identification.
2. Revision number (FDIO locations only).
2A. Strip request originator. (At FDIO locations this indicates the sector or position that requested a strip be printed.)
3. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
4. Computer identification number if required.
5. Secondary radar (beacon) code assigned.
6. (FDIO Locations.) The previous fix will be printed.(Non-FDIO Locations.) Use of the inbound airway. This function is restricted to facilities where flight data is received via interphone when agreed upon by the center and terminal facilities.
7. Coordination fix.
8. Estimated time of arrival at the coordination fix or destination airport.
8A. OPTIONAL USE.
8B. OPTIONAL USE, when voice recorders are operational; REQUIRED USE, when the voice recorders are not operating and strips are being used at the facility. This space is used to record reported RA events when the voice recorders are not operational and strips are being used at the facility. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
9. Altitude (in hundreds of feet) and remarks.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i. e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
9A. Minimum fuel, destination airport/point out/radar vector/speed adjustment information. Air traffic managers may authorize in a facility directive the omission of any of these items, except minimum fuel, if no misunderstanding will result.
NOTE- Authorized omissions and optional use of spaces shall be specified in the facility directive concerning strip marking procedures.
9B. OPTIONAL USE.
9C. OPTIONAL USE.
10-18. Enter data as specified by a facility directive. Radar facility personnel need not enter data in these spaces except when nonradar procedures are used or when radio recording equipment is inoperative.
b. Departures: Information recorded on the flight progress strips (FAA Forms 7230-7.1, 7230-7.2, and 7230-8) shall be entered in the correspondingly numbered spaces. Facility managers can authorize omissions and/or optional use of spaces 2A, 8A, 8B, 9A, 9B, 9C, and 10-18, if no misunderstanding will result. These omissions and/or optional uses shall be specified in a facility directive.
Block Information Recorded
1. Aircraft identification.
2. Revision number (FDIO locations only).
2A. Strip request originator. (At FDIO locations this indicates the sector or position that requested a strip be printed.)
3. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
4. Computer identification number if required.
5. Secondary radar (beacon) code assigned.
6. Proposed departure time.
7. Requested altitude.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i. e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
8. Departure airport.
8A. OPTIONAL USE.
8B. OPTIONAL USE, when voice recorders are operational;
REQUIRED USE, when the voice recorders are not operating and strips are being used at the facility. This space is used to record reported RA events when the voice recorders are not operational and strips are being used at the facility. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
9. Computer-generated: Route, destination, and remarks. Manually enter altitude/altitude restrictions in the order flown, if appropriate, and remarks.
9. Hand-prepared: Clearance limit, route, altitude/altitude restrictions in the order flown, if appropriate, and remarks.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
9A. OPTIONAL USE.
9B. OPTIONAL USE.
9C. OPTIONAL USE.
10-18. Enter data as specified by a facility directive. Items, such as departure time, runway used for takeoff, check marks to indicate information forwarded or relayed, may be entered in these spaces.
c. Overflights: Information recorded on the flight progress strips (FAA Forms 7230-7.1, 7230-7.2, and 7230-8) shall be entered in the correspondingly numbered spaces. Facility managers can authorize omissions and/or optional use of spaces 2A, 8A, 8B, 9A, 9B, 9C, and 10-18, if no misunderstanding will result. These omissions and/or optional uses shall be specified in a facility directive.
Block Information Recorded
1. Aircraft identification.
2. Revision number (FDIO locations only).
2A. Strip request originator. (At FDIO locations this indicates the sector or position that requested a strip be printed.)
3. Number of aircraft if more than one, heavy aircraft indicator “H/” if appropriate, type of aircraft, and aircraft equipment suffix.
4. Computer identification number if required.
5. Secondary radar (beacon) code assigned.
6. Coordination fix.
7. Overflight coordination indicator (FDIO locations only).
NOTE- The overflight coordination indicator identifies the facility to which flight data has been forwarded.
8. Estimated time of arrival at the coordination fix.
8A. OPTIONAL USE.
8B. OPTIONAL USE, when voice recorders are operational;
REQUIRED USE, when the voice recorders are not operating and strips are being used at the facility. This space is used to record reported RA events when the voice recorders are not operational and strips are being used at the facility. The letters RA followed by a climb or descent arrow (if the climb or descent action is reported) and the time (hhmm) the event is reported.
9. Altitude and route of flight through the terminal area.
NOTE- Altitude information may be written in thousands of feet provided the procedure is authorized by the facility manager, and is defined in a facility directive, i.e., FL 230 as 23, 5,000 feet as 5, and 2,800 as 2.8.
9A. OPTIONAL USE.
9B. OPTIONAL USE.
9C. OPTIONAL USE.
10-18. Enter data as specified by a facility directive.
NOTE- National standardization of items (10 through 18) is not practical because of regional and local variations in operating methods; e.g., single fix, multiple fix, radar, tower en route control, etc.
d. Air traffic managers at automated terminal radar facilities may waive the requirement to use flight progress strips provided:
1. Backup systems such as multiple radar sites/systems or single site radars with CENRAP are utilized.
2. Local procedures are documented in a facility directive. These procedures should include but not be limited to:
(a) Departure areas and/or procedures.
(b) Arrival procedures.
(c) Overflight handling procedures.
(d) Transition from radar to nonradar.
(e) Transition from ARTS to non-ARTS.
(f) Transition from ASR to CENRAP.
(g) Transition to or from ESL.
3. No misunderstanding will occur as a result of no strip usage.
4. Unused flight progress strips, facility developed forms and/or blank notepads shall be provided for controller use.
5. Facilities shall revert to flight progress strip usage if backup systems referred to in subpara d1 are not available.
e. Air traffic managers at FDIO locations may authorize reduced lateral spacing between fields so as to print all FDIO data to the left of the strip perforation. When using FAA Form 7230-7.2, all items will retain the same relationship to each other as they do when the full length strip (FAA Form 7230-7.1) is used.
AIRCRAFT IDENTITY
Indicate aircraft identity by one of the following using combinations not to exceed seven alphanumeric characters:
a. Civil aircraft, including air-carrier aircraft letter-digit registration number including the letter “T” prefix for air taxi aircraft, the letter “L” for lifeguard aircraft, 3-letter aircraft company designator specified in FAAO JO 7340.2, Contractions, followed by the trip or flight number. Use the operating air carrier’s company name in identifying equipment interchange flights.
EXAMPLE-
“N12345.”
“TN5552Q.”
“AAl192.”
“LN751B.”
NOTE- The letter “L” is not to be used for air carrier/air taxi lifeguard aircraft.
b. Military Aircraft.
1. Prefixes indicating branch of service and/or type of mission followed by the last 5 digits of the serial number (the last 4 digits for CFC and CTG).
2. Pronounceable words of 3, 4, 5, and 6 letters followed by a 4-, 3-, 2-, or 1-digit number.
EXAMPLE- “SAMP Three One Six.”
3. Assigned double-letter 2-digit flight number.
4. Navy or Marine fleet and training command aircraft, one of the following:
(a) The service prefix and 2 letters (use phonetic alphabet equivalent) followed by 2 or 3 digits.
Branch of Service Prefix
Prefix Branch
A U.S. Air Force
C U.S. Coast Guard
G Air or Army National Guard
R U.S. Army
VM U.S. Marine Corps
VV U.S. Navy
CFC Canadian Forces
CTG Canadian Coast Guard
Military Mission Prefix
Prefix Mission
E Medical Air Evacuation
F Flight Check
L LOGAIR (USAF Contract)
RCH AMC (Air Mobility Command)
S Special Air Mission
(b) The service prefix and a digit and a letter (use phonetic alphabet equivalent) followed by 2 or 3 digits.
c. Special-use. Approved special-use identifiers.
REDUCED VERTICAL SEPARATION MINIMUM (RVSM). Prior to conducting RVSM operations within the U.S., the operator must obtain authorization from the FAA or from the responsible authority, as appropriate.
/J /E with RVSM
/K /F with RVSM
/L /G with RVSM
/Q /R with RVSM
/W RVSM
Clearance Abbreviations
Abbreviation Meaning
A Cleared to airport (point of intended landing)
B Center clearance delivered
C ATC clears (when clearance relayed through non-ATC facility)
CAF Cleared as filed
D Cleared to depart from the fix
F Cleared to the fix
H Cleared to hold and instructions issued
L Cleared to land
N Clearance not delivered
O Cleared to the outer marker
PD Cleared to climb/descend at pilot’s discretion
Q Cleared to fly specified sectors of a NAVAID defined in terms of courses, bearings, radials or quadrants within a designated radius.
T Cleared through (for landing and takeoff through intermediate point)
V Cleared over the fix
X Cleared to cross (airway, route, radial) at (point)
Z Tower jurisdiction
Miscellaneous Abbreviations
Abbreviation Meaning
BC Back course approach
CT Contact approach
FA Final approach
FMS Flight management system approach
GPS GPS approach
I Initial approach
ILS ILS approach
MA Missed approach
MLS MLS approach
NDB Nondirectional radio beacon approach
OTP VFR conditions-on-top
PA Precision approach
PT Procedure turn
RA Resolution advisory (Pilot reported TCAS event)
RH Runway heading
RNAV Area navigation approach
RP Report immediately upon passing (fix/altitude)
RX Report crossing
SA Surveillance approach
SI Straight-in approach
TA TACAN approach
TL Turn left
TR Turn right
VA Visual approach
VR VOR approach
11
Radio and Interphone Communications
RADIO COMMUNICATIONS
Use radio frequencies for the special purposes for which they are intended. A single frequency may be used for more than one function except as follows:
TERMINAL. When combining positions in the tower, do not use ground control frequency for airborne communications.
NOTE- Due to the limited number of frequencies assigned to towers for the ground control function, it is very likely that airborne use of a ground control frequency could cause interference to other towers or interference to your aircraft from another tower. When combining these functions, it is recommended combining them on local control. The ATIS may be used to specify the desired frequency.
MONITORING
Monitor interphones and assigned radio frequencies continuously.
NOTE- Although all FAA facilities, including RAPCONs and RATCFs, are required to monitor all assigned frequencies continuously, USAF facilities may not monitor all unpublished discrete frequencies.
PILOT ACKNOWLEDGMENT/READ BACK
a. When issuing clearances or instructions ensure acknowledgment by the pilot.
NOTE- Pilots may acknowledge clearances, instructions, or other information by using “Wilco,” “Roger,” “Affirmative,” or other words or remarks.
b. If altitude, heading, or other items are read back by the pilot, ensure the read back is correct. If incorrect or incomplete, make corrections as appropriate.
AUTHORIZED INTERRUPTIONS
As necessary, authorize a pilot to interrupt his/her communications guard.
NOTE- Some users have adopted procedures to insure uninterrupted receiving capability with ATC when a pilot with only one operative communications radio must interrupt his/her communications guard because of a safety related problem requiring airborne communications with his/her company. In this event, pilots will request approval to abandon guard on the assigned ATC frequency for a mutually agreeable time period. Additionally, they will inform controllers of the NAVAID voice facility and the company frequency they will monitor.
AUTHORIZED TRANSMISSIONS
Transmit only those messages necessary for air traffic control or otherwise contributing to air safety.
FALSE OR DECEPTIVE COMMUNICATIONS
Take action to detect, prevent, and report false, deceptive, or phantom controller communications to an aircraft or controller. The following shall be accomplished when false or deceptive communications occur:
a. Correct false information.
b. Broadcast an alert to aircraft operating on all frequencies within the area where deceptive or phantom transmissions have been received.
EXAMPLE- “Attention all aircraft. False ATC instructions have been received in the area of Long Beach Airport. Exercise extreme caution on all frequencies and verify instructions.”
c. Collect pertinent information regarding the incident.
d. Notify the operations supervisor of the false, deceptive, or phantom transmission and report all relevant information pertaining to the incident.
AUTHORIZED RELAYS
a. Relay operational information to aircraft or aircraft operators as necessary. Do not agree to handle such messages on a regular basis. Give the source of any such message you relay.
b. Relay official FAA messages as required.
NOTE- The FAA Administrator and Deputy Administrator will sometimes use code phrases to identify themselves in air-to-ground communications as follows:
Administrator: “SAFEAIR ONE.”
Deputy Administrator: “SAFEAIR TWO.”
EXAMPLE- “Miami Center, Jetstar One, this is SAFEAIR ONE, (message).”
c. Relay operational information to military aircraft operating on, or planning to operate on IRs.
RADIO MESSAGE FORMAT
Use the following format for radio communications with an aircraft:
a. Sector/position on initial radio contact:
1. Identification of aircraft.
2. Identification of ATC unit.
3. Message (if any).
4. The word “over” if required.
b. Subsequent radio transmissions from the same sector/position shall use the same format, except the identification of the ATC unit may be omitted.
TERMINAL. You may omit aircraft identification after initial contact when conducting the final portion of a radar approach.
ABBREVIATED TRANSMISSIONS
Transmissions may be abbreviated as follows:
a. Use the identification prefix and the last 3 digits or letters of the aircraft identification after communications have been established. Do not abbreviate similar sounding aircraft identifications or the identification of an air carrier or other civil aircraft having an FAA authorized call sign.
b. Omit the facility identification after communication has been established.
c. Transmit the message immediately after the callup (without waiting for the aircraft’s reply) when the message is short and receipt is generally assured.
d. Omit the word “over” if the message obviously requires a reply.
INTERPHONE TRANSMISSION PRIORITIES
Give priority to interphone transmissions as follows:
a. First priority. Emergency messages including essential information on aircraft accidents or suspected accidents. After an actual emergency has passed, give a lower priority to messages relating to that accident.
b. Second priority. Clearances and control instructions.
c. Third priority. Movement and control messages using the following order of preference when possible:
1. Progress reports.
2. Departure or arrival reports.
3. Flight plans.
d. Fourth priority. Movement messages on VFR aircraft.
PRIORITY INTERRUPTION
Use the words “emergency” or “control” for interrupting lower priority messages when you have an emergency or control message to transmit.
INTERPHONE MESSAGE FORMAT
Use the following format for interphone intra/interfacility communications:
a. Both the caller and receiver identify their facility and/or position in a manner that insures they will not be confused with another position.
NOTE- Other means of identifying a position, such as substituting departure or arrival gate/fix names for position identification, may be used. However, it must be operationally beneficial, and the procedure fully covered in a letter of agreement or a facility directive, as appropriate.
EXAMPLE- Caller: “Albuquerque Center Sixty Three, Amarillo Departure.”
Receiver: “Albuquerque Center.”
b. Between two facilities which utilize numeric position identification, the caller must identify both facility and position.
EXAMPLE- Caller: “Albuquerque Sixty Three, Fort Worth Eighty Two.”
c. Caller states the type of coordination to be accomplished when advantageous. For example, handoff or APREQ.
d. The caller states the message.
e. The receiver states the response to the caller’s message followed by the receiver’s operating initials.
f. The caller states his or her operating initials.
EXAMPLE-
1. Caller: “Denver High, R Twenty-five.”
Receiver: “Denver High.”
Caller: “Request direct Denver for Northwest Three Twenty-eight.”
Receiver: “Northwest Three Twenty-eight direct Denver approved. H.F.”
Caller: “G.M.”
2. Receiver: “Denver High, Go ahead override.”
Caller: “R Twenty-five, Request direct Denver for Northwest Three Twenty-eight.”
Receiver: “Northwest Three Twenty-eight direct Denver approved. H.F.”
Caller: “G.M.”
3. Caller: (“Bolos” is a departure gate in Houston ARTCC’s Sabine sector)-”Bolos, Houston local.”
Receiver: “Bolos.”
Caller: “Request Flight Level three five zero for American Twenty-five.”
Receiver: “American Twenty-five Flight Level three five zero approved, A.C.”
Caller: “G.M.”
4. Caller: “Sector Twelve, Ontario Approach, APREQ.”
Receiver: “Sector Twelve.”
Caller: “Cactus Five forty-two heading one three zero and climbing to one four thousand.”
Receiver: “Cactus Five forty-two heading one three zero and climbing to one four thousand approved. B.N.”
Caller: “A.M.”
5. Caller: “Zanesville, Columbus, seventy-three line, handoff.”
Receiver: “Zanesville.”
Caller: “Five miles east of Appleton VOR, United Three Sixty-six.”
Receiver: “United Three Sixty-six, radar contact, A.Z.”
Caller: “M.E.”
g. Identify the interphone voice line on which the call is being made when two or more such lines are collocated at the receiving operating position.
EXAMPLE- “Washington Center, Washington Approach on the Fifty Seven line.”
“Chicago Center, O’Hare Tower handoff on the Departure West line.”
h. TERMINAL. The provisions of subparas a, b, c, e, f, g, Interphone Message Termination, may be omitted provided:
1. Abbreviated standard coordination procedures are contained in a facility directive describing the specific conditions and positions that may utilize an abbreviated interphone message format; and
2. There will be no possibility of misunderstanding which positions are using the abbreviated procedures.
INTERPHONE MESSAGE TERMINATION
Terminate interphone messages with your operating initials.
WORDS AND PHRASES
a. Use the words or phrases in radiotelephone and interphone communication as contained in the P/CG or, within areas where Controller Pilot Data Link Communications (CPDLC) is in use, the phraseology contained in the applicable CPDLC message set.
b. The word “heavy” shall be used as part of the identification of heavy jet aircraft as follows:
TERMINAL. In all communications with or about heavy jet aircraft.
EN ROUTE. The use of the word heavy may be omitted except as follows:
1. In communications with a terminal facility about heavy jet operations.
2. In communications with or about heavy jet aircraft with regard to an airport where the en route center is providing approach control service.
3. In communications with or about heavy jet aircraft when the separation from a following aircraft may become less than 5 miles by approved procedure.
4. When issuing traffic advisories.
EXAMPLE- “United Fifty-Eight Heavy.”
NOTE- Most airlines will use the word “heavy” following the company prefix and flight number when establishing communications or when changing frequencies within a terminal facility’s area.
5. When in radio communications with “Air Force One” or “Air Force Two,” do not add the heavy designator to the call sign. State only the call sign “Air Force One/Two” regardless of the type aircraft.
EMPHASIS FOR CLARITY
Emphasize appropriate digits, letters, or similar sounding words to aid in distinguishing between similar sounding aircraft identifications. Additionally:
a. Notify each pilot concerned when communicating with aircraft having similar sounding identifications.
EXAMPLE- “United Thirty-one United, Miami Center, U.S. Air Thirty-one is also on this frequency, acknowledge.”
“U.S. Air Thirty-one U.S. Air, Miami Center, United Thirty-one is also on this frequency, acknowledge.”
b. Notify the operations supervisor-in-charge of any duplicate flight identification numbers or phonetically similar-sounding call signs when the aircraft are operating simultaneously within the same sector.
NOTE- This is especially important when this occurs on a repetitive, rather than an isolated, basis.
WEATHER AND CHAFF SERVICES
a. Issue pertinent information on observed/reported weather and chaff areas. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas.
1. Issue weather and chaff information by defining the area of coverage in terms of azimuth (by referring to the 12-hour clock) and distance from the aircraft or by indicating the general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.
PHRASEOLOGY- WEATHER/CHAFF AREA BETWEEN (number)O’CLOCK AND (number) O’CLOCK (number) MILES, or (number) MILE BAND OF WEATHER/CHAFF FROM (fix or number of miles and direction from fix) TO (fix or number of miles and direction from fix).
2. When a deviation cannot be approved as requested and the situation permits, suggest an alternative course of action.
PHRASEOLOGY- UNABLE DEVIATION (state possible alternate course of action).
FLY HEADING (heading), or PROCEED DIRECT (name of NAVAID).
b. In areas of significant weather, plan ahead and be prepared to suggest, upon pilot request, the use of alternative routes/altitudes.
PHRASEOLOGY- DEVIATION APPROVED, (restrictions if necessary), ADVISE WHEN ABLE TO:
RETURN TO COURSE, or RESUME OWN NAVIGATION, or FLY HEADING (heading), or PROCEED DIRECT (name of NAVAID).
NOTE- Weather significant to the safety of aircraft includes such conditions as funnel cloud activity, lines of thunderstorms, embedded thunderstorms, large hail, wind shear, microbursts, moderate to extreme turbulence (including CAT), and light to severe icing.
c. Inform any tower for which you provide approach control services of observed precipitation on radar which is likely to affect their operations.
d. Use the term “precipitation” when describing radar-derived weather. Issue the precipitation intensity from the lowest descriptor (LIGHT) to the highest descriptor (EXTREME) when that information is available. Do not use the word “turbulence” in describing radar-derived weather.
1. LIGHT.
2. MODERATE.
3. HEAVY.
4. EXTREME.
NOTE- Weather and Radar Processor (WARP) does not display light intensity.
PHRASEOLOGY- (Intensity) PRECIPITATION BETWEEN (number) O’CLOCK AND (number) O’CLOCK, (number) MILES. MOVING (direction) AT (number) KNOTS, TOPS (altitude). PRECIPITATION AREA IS (number) MILES IN DIAMETER.
EXAMPLE- 1. “Extreme precipitation between eleven o’clock and one o’clock, one zero miles moving east at two zero knots, tops flight level three niner zero.” 2. “Heavy precipitation between ten o’clock and two o’clock, one five miles. Precipitation area is two five miles in diameter.” 3. “Heavy to Extreme precipitation between ten o’clock and two o’clock, one five miles. Precipitation area is two five miles in diameter.”
e. When precipitation intensity information is not available.
PHRASEOLOGY- PRECIPITATION BETWEEN (number) O’CLOCK AND (number) O’CLOCK, (number) MILES. MOVING (direction) AT (number) KNOTS, TOPS (altitude), PRECIPITATION AREA IS (number) MILES IN DIAMETER, INTENSITY UNKNOWN.
EXAMPLE- “Precipitation area between one o’clock and three o’clock three five miles. Precipitation area is three zero miles in diameter, intensity unknown.”
NOTE- Phraseology using precipitation intensity descriptions is only applicable when the radar precipitation intensity information is determined by NWS radar equipment or NAS ground based digitized radar equipment with weather capabilities. This precipitation may not reach the surface.
f. EN ROUTE. When issuing Air Route Surveillance Radar (ARSR) precipitation intensity use the following:
1. Describe the lowest displayable precipitation intensity as MODERATE.
2. Describe the highest displayable precipitation intensity as HEAVY to EXTREME.
PHRASEOLOGY- (Intensity) PRECIPITATION BETWEEN (number) O’CLOCK AND (number) O’CLOCK, (number) MILES MOVING (direction) AT (number) KNOTS, TOPS (altitude) PRECIPITATION AREA IS (number) MILES IN DIAMETER.
EXAMPLE- “Moderate precipitation between ten o’clock and one o’clock, three zero miles. Precipitation area is five zero miles in diameter.”
“Moderate to extreme precipitation twelve o’clock and three o’clock, seven zero miles. Precipitation area is one zero zero miles in diameter.”
g. When operational/equipment limitations exist, controllers shall ensure that the highest available level of precipitation intensity within their area of jurisdiction is displayed.
h. The supervisory traffic management coordinator-in-charge/operations supervisor/controller-in-charge shall verify the digitized radar weather information by the best means available (e.g., pilot reports, local tower personnel, etc.) if the weather data displayed by digitized radar is reported as questionable or erroneous. Errors in weather radar presentation shall be reported to the technical operations technician and the air traffic supervisor shall determine if the digitized radar derived weather data is to be displayed and a NOTAM distributed.
NOTE- Anomalous propagation (AP) is a natural occurrence affecting radar and does not in itself constitute a weather circuit failure.
CALM WIND CONDITIONS
TERMINAL. Describe the wind as calm when the wind velocity is less than three knots.
REPORTING WEATHER CONDITIONS
a. When the prevailing visibility at the usual point of observation, or at the tower level, is less than 4 miles, tower personnel shall take prevailing visibility observations and apply the observations as follows:
1. Use the lower of the two observations (tower or surface) for aircraft operations.
2. Forward tower visibility observations to the weather observer.
3. Notify the weather observer when the tower observes the prevailing visibility decrease to less than 4 miles or increase to 4 miles or more.
b. Forward current weather changes to the appropriate control facility as follows:
1. When the official weather changes to a condition which is below 1,000-foot ceiling or below the highest circling minimum, whichever is greater, or less than 3 miles visibility, and when it improves to a condition which is better than those above.
2. Changes which are classified as special weather observations during the time that weather conditions are below 1,000-foot ceiling or the highest circling minimum, whichever is greater, or less than 3 miles visibility.
c. Towers at airports where military turbo-jet en route descents are routinely conducted shall also report the conditions to the ARTCC even if it is not the controlling facility.
d. If the receiving facility informs you that weather reports are not required for a specific time period, discontinue the reports. The time period specified should not exceed the duration of the receiving controller’s tour of duty.
e. EN ROUTE. When you determine that weather reports for an airport will not be required for a specific time period, inform the AFSS/FSS or tower of this determination. The time period specified should not exceed the duration of receiving controller’s tour of duty.
DISSEMINATING WEATHER INFORMATION
TERMINAL. Observed elements of weather information shall be disseminated as follows:
a. General weather information, such as “large breaks in the overcast,” “visibility lowering to the south,” or similar statements which do not include specific values, and any elements derived directly from instruments, pilots, or radar may be transmitted to pilots or other ATC facilities without consulting the weather reporting station.
b. Specific values, such as ceiling and visibility, may be transmitted if obtained by one of the following means:
1. You are properly certificated and acting as official weather observer for the elements being reported.
NOTE- USAF controllers do not serve as official weather observers.
2. You have obtained the information from the official observer for the elements being reported.
3. The weather report was composed or verified by the weather station.
4. The information is obtained from an official Automated Weather Observation System (AWOS) or an Automated Surface Observation System (ASOS).
c. Differences between weather elements observed from the tower and those reported by the weather station shall be reported to the official observer for the element concerned.
Altimeter Settings
CURRENT SETTINGS
a. Current altimeter settings shall be obtained from direct-reading instruments or directly from weather reporting stations.
b. If a pilot requests the altimeter setting in millibars, ask the nearest weather reporting station for the equivalent millibar setting.
c. USAF/USA. Use the term “Estimated Altimeter” for altimeter settings reported or received as estimated.
ALTIMETER SETTING ISSUANCE BELOW LOWEST USABLE FL
a. TERMINAL. Identify the source of an altimeter setting when issued for a location other than the aircraft’s departure or destination airport.
b. EN ROUTE. Identify the source of all altimeter settings when issued.
PHRASEOLOGY- THE (facility name) (time of report if more than one hour old) ALTIMETER (setting).
c. Issue the altimeter setting:
1. To en route aircraft at least one time while operating in your area of jurisdiction. Issue the setting for the nearest reporting station along the aircraft’s route of flight:
2. TERMINAL. To all departures. Unless specifically requested by the pilot, the altimeter setting need not be issued to local aircraft operators who have requested this omission in writing or to scheduled air carriers.
3. TERMINAL. To arriving aircraft on initial contact or as soon as possible thereafter. The tower may omit the altimeter if the aircraft is sequenced or vectored to the airport by the approach control having jurisdiction at that facility.
4. EN ROUTE. For the destination airport to arriving aircraft, approximately 50 miles from the destination, if an approach control facility does not serve the airport.
5. In addition to the altimeter setting provided on initial contact, issue changes in altimeter setting to aircraft executing a nonprecision instrument approach as frequently as practical when the official weather report includes the remarks “pressure falling rapidly.”
d. If the altimeter setting must be obtained by the pilot of an arriving aircraft from another source, instruct the pilot to obtain the altimeter setting from that source.
NOTE- 1. The destination altimeter setting, whether from a local or remote source, is the setting upon which the instrument approach is predicated. 2. Approach charts for many locations specify the source of altimeter settings as non-FAA facilities, such as UNICOMs.
e. When issuing clearance to descend below the lowest usable flight level, advise the pilot of the altimeter setting of the weather reporting station nearest the point the aircraft will descend below that flight level.
f. Department of Defense (DOD) aircraft which operate on “single altimeter settings” (CFR Exemption 2861A) shall be issued altimeter settings in accordance with standard procedures while the aircraft are en route to and from their restricted areas, MOAs, and ATC assigned airspace areas.
g. When the barometric pressure is greater than 31.00 inches Hg., issue the altimeter setting and:
1. En Route/Arrivals. Advise pilots to remain set on altimeter 31.00 until reaching final approach segment.
2. Departures. Advise pilots to set altimeter 31.00 prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower.
PHRASEOLOGY- ALTIMETER, THREE ONE TWO FIVE, SET THREE ONE ZERO ZERO UNTIL REACHING THE FINAL APPROACH FIX. or ALTIMETER, THREE ONE ONE ZERO, SET THREE ONE ZERO ZERO PRIOR TO REACHING ONE THOUSAND THREE HUNDRED.
NOTE- 1. Aircraft with Mode C altitude reporting will be displayed on the controller’s radar scope with a uniform altitude offset above the assigned altitude. With an actual altimeter of 31.28 inches Hg, the Mode C equipped aircraft will show 3,300 feet when assigned 3,000 feet. This will occur unless local directives authorize entering the altimeter setting 31.00 into the computer system regardless of the actual barometric pressure. 2. Flight Standards will implement high barometric pressure procedures by NOTAM defining the geographic area affected. 3. Airports unable to accurately measure barometric pressures above 31.00 inches Hg. will report the barometric pressure as “missing” or “in excess of 31.00 inches of Hg.” Flight operations to or from those airports are restricted to VFR weather conditions.
Runway Visibility Reporting- Terminal
FURNISH RVR/RVV VALUES
Where RVR or RVV equipment is operational, irrespective of subsequent operation or nonoperation of navigational or visual aids for the application of RVR/RVV as a takeoff or landing minima, furnish the values for the runway in use in accordance Terminology.
NOTE- Readout capability of different type/model RVR equipment varies. For example, older equipment minimum readout value is 600 feet. Newer equipment may have minimum readout capability as low as 100 feet. Readout value increments also may differ. Older equipment have minimum readout increments of 200 feet. New equipment increments below 800 feet are 100 feet.
ARRIVAL/DEPARTURE RUNWAY VISIBILITY
a. Issue current touchdown RVR/RVV for the runway(s) in use:
1. When prevailing visibility is 1 mile or less regardless of the value indicated.
2. When RVR/RVV indicates a reportable value regardless of the prevailing visibility.
NOTE- Reportable values are: RVR 6,000 feet or less; RVV 11/2 miles or less.
3. When it is determined from a reliable source that the indicated RVR value differs by more than 400 feet from the actual conditions within the area of the transmissometer, the RVR data is not acceptable and shall not be reported.
NOTE- A reliable source is considered to be a certified weather observer, automated weather observing system, air traffic controller, flight service specialist, or pilot.
4. When the observer has reliable reports, or has otherwise determined that the instrument values are not representative of the associated runway, the data shall not be used.
b. Issue both mid-point and roll-out RVR when the value of either is less than 2,000 feet and the touchdown RVR is greater than the mid-point or roll-out RVR.
c. Local control shall issue the current RVR/RVV to each aircraft prior to landing or departure in accordance with subparas a and b.
TERMINOLOGY
a. Provide RVR/RVV information by stating the runway, the abbreviation RVR/RVV, and the indicated value. When issued along with other weather elements, transmit these values in the normal sequence used for weather reporting.
EXAMPLE- “Runway One Four RVR Two Thousand Four Hundred.”
“Runway Three Two RVV Three Quarters.”
b. When two or more RVR systems serve the runway in use, report the indicated values for the different systems in terms of touchdown, mid, and rollout as appropriate.
EXAMPLE- “Runway Two Two Left RVR Two Thousand, rollout One Thousand Eight Hundred.”
“Runway Two Seven Right RVR One Thousand, mid Eight Hundred, rollout Six Hundred.”
c. When there is a requirement to issue an RVR or RVV value and a visibility condition greater or less than the reportable values of the equipment is indicated, state the condition as “MORE THAN” or “LESS THAN” the appropriate minimum or maximum readable value.
EXAMPLE- “Runway Three Six RVR more than Six Thousand.”
“Runway Niner RVR One Thousand, rollout less than Six Hundred.”
d. When a readout indicates a rapidly varying visibility condition (1,000 feet or more for RVR; one or more reportable values for RVV), report the current value followed by the range of visibility variance.
EXAMPLE- “Runway Two Four RVR Two Thousand, variable One Thousand Six Hundred to Three Thousand.”
“Runway Three One RVV Three-quarters, variable One-quarter to One.”
Automatic Terminal Information Service Procedures
APPLICATION: Use the ATIS, where available, to provide advance noncontrol airport/terminal area and meteorological information to aircraft.
a. Identify each ATIS message by a phonetic letter code word at both the beginning and the end of the message. Automated systems will have the phonetic letter code automatically appended. Exceptions may be made where omissions are required because of special programs or equipment.
1. Each alphabet letter phonetic word shall be used sequentially, except as authorized in subpara a2, beginning with “Alpha,” ending with “Zulu,” and repeated without regard to the beginning of a new day. Identify the first resumed broadcast message with “Alpha” or the first assigned alphabet letter word in the event of a broadcast interruption of more than 12 hours.
2. Specific sequential portions of the alphabet may be assigned between facilities or an arrival and departure ATIS when designated by a letter of agreement or facility directive.
b. The ATIS recording shall be reviewed for completeness, accuracy, speech rate, and proper enunciation before being transmitted.
c. Arrival and departure messages, when broadcast separately, need only contain information appropriate for that operation.
OPERATING PROCEDURES
Maintain an ATIS message that reflects the most current arrival and departure information.
a. Make a new recording when any of the following occur:
1. Upon receipt of any new official weather regardless of whether there is or is not a change in values.
2. When runway braking action reports are received that indicate runway braking is worse than that which is included in the current ATIS broadcast.
3. When there is a change in any other pertinent data, such as runway change, instrument approach in use, new or canceled NOTAMs/PIREPs/HIWAS update, etc.
b. When a pilot acknowledges that he/she has received the ATIS broadcast, controllers may omit those items contained in the broadcasts if they are current. Rapidly changing conditions will be issued by ATC, and the ATIS will contain the following:
EXAMPLE- “Latest ceiling/visibility/altimeter/wind/(other conditions) will be issued by approach control/tower.”
c. Broadcast on all appropriate frequencies to advise aircraft of a change in the ATIS code/message.
d. Controllers shall ensure that pilots receive the most current pertinent information. Ask the pilot to confirm receipt of the current ATIS information if the pilot does not initially state the appropriate ATIS code. Controllers shall ensure that changes to pertinent operational information is provided after the initial confirmation of ATIS information is established. Issue the current weather, runway in use, approach information, and pertinent NOTAMs to pilots who are unable to receive the ATIS.
EXAMPLE- “Verify you have information ALPHA.”
“Information BRAVO now current, visibility three miles.”
“Information CHARLIE now current, Ceiling 1500 Broken.”
“Information CHARLIE now current, advise when you have CHARLIE.”
CONTENT: Include the following in ATIS broadcast as appropriate:
a. Airport/facility name, phonetic letter code, time of weather sequence (UTC). Weather information consisting of wind direction and velocity, visibility, obstructions to vision, present weather, sky condition, temperature, dew point, altimeter, a density altitude advisory when appropriate and other pertinent remarks included in the official weather observation. Wind direction, velocity, and altimeter shall be reported from certified direct reading instruments. Temperature and dew point should be reported from certified direct reading sensors when available. Always include weather observation remarks of lightning, cumulonimbus, and towering cumulus clouds.
NOTE- ASOS/AWOS is to be considered the primary source of wind direction, velocity, and altimeter data for weather observation purposes at those locations that are so equipped. The ASOS Operator Interface Device (OID) displays the magnetic wind as “MAG WND” in the auxiliary data location in the lower left-hand portion of the screen. Other OID displayed winds are true and are not to be used for operational purposes.
b. Man-Portable Air Defense Systems (MANPADS) alert and advisory. Specify the nature and location of threat or incident, whether reported or observed and by whom, time (if known), and notification to pilots to advise ATC if they need to divert.
EXAMPLE- 1. “MANPADS alert. Exercise extreme caution. MANPADS threat reported by TSA, Chicago area.” “Advise on initial contact if you want to divert.” 2. “MANPADS alert. Exercise extreme caution. MANPADS attack observed by tower one-half mile northwest of airfield at one-two-five-zero Zulu.” “Advise on initial contact if you want to divert.”
c. Terminal facilities shall include reported unauthorized laser illumination events on the ATIS broadcast for one hour following the last report. Include the time, location, altitude, color, and direction of the laser as reported by the pilot.
PHRASEOLOGY- UNAUTHORIZED LASER ILLUMINATION EVENT, (UTC time), (location), (altitude), (color), (direction).
EXAMPLE- UNAUTHORIZED LASER ILLUMINATION EVENT, AT 0100z, 8 MILE FINAL RUNWAY 18R AT 3,000 FEET, GREEN LASER FROM THE SOUTHWEST.
d. The ceiling/sky condition, visibility, and obstructions to vision may be omitted if the ceiling is above 5,000 feet and the visibility is more than 5 miles.
EXAMPLE- A remark may be made, “The weather is better than five thousand and five.”
e. Instrument/visual approach/s in use. Specify landing runway/s unless the runway is that to which the instrument approach is made.
f. Departure runway/s (to be given only if different from landing runway/s or in the instance of a “departure only” ATIS).
g. Taxiway closures which affect the entrance or exit of active runways, other closures which impact airport operations, other NOTAMs and PIREPs pertinent to operations in the terminal area. Inform pilots of where hazardous weather is occurring and how the information may be obtained. Include available information of known bird activity.
h. Runway braking action or friction reports when provided. Include the time of the report and a word describing the cause of the runway friction problem.
PHRASEOLOGY- RUNWAY (number) MU (first value, second value, third value) AT (time), (cause).
EXAMPLE- “Runway Two Seven, MU forty-two, forty-one, twenty-eight at one zero one eight Zulu, ice.”
i. Other optional information as local conditions dictate in coordination with ATC. This may include such items as VFR arrival frequencies, temporary airport conditions, LAHSO operations being con-ducted, or other perishable items that may appear only for a matter of hours or a few days on the ATIS message.
j. Low level wind shear/microburst when reported by pilots or is detected on a wind shear detection system.
k. A statement which advises the pilot to read back instructions to hold short of a runway. The air traffic manager may elect to remove this requirement 60 days after implementation provided that removing the statement from the ATIS does not result in increased requests from aircraft for read back of hold short instructions.
l. Instructions for the pilot to acknowledge receipt of the ATIS message by informing the controller on initial contact.
EXAMPLE- “Boston Tower Information Delta. One four zero zero Zulu. Wind two five zero at one zero. Visibility one zero. Ceiling four thousand five hundred broken. Temperature three four. Dew point two eight. Altimeter three zero one zero. ILS-DME Runway Two Seven Approach in use. Departing Runway Two Two Right. Hazardous Weather Information for (geographical area) available on HIWAS, Flight Watch, or Flight Service Frequencies. Advise on initial contact you have Delta.”
Team Position Responsibilities
EN ROUTE SECTOR TEAM POSITION RESPONSIBILITIES
a. En Route Sector Team Concept and Intent:
1. There are no absolute divisions of responsibilities regarding position operations. The tasks to be completed remain the same whether one, two, or three people are working positions within a sector. The team, as a whole, has responsibility for the safe and efficient operation of that sector.
2. The intent of the team concept is not to hold the team accountable for the action of individual members, in the event of an operational accident/incident.
b. Terms. The following terms will be used in en route facilities for the purpose of standardization:
1. Sector. The area of control responsibility (delegated airspace) of the en route sector team, and the team as a whole.
2. Radar Position (R). That position which is in direct communication with the aircraft and which uses radar information as the primary means of separation.
3. Radar Associate (RA). That position sometimes referred to as “D-Side” or “Manual Controller.”
4. Radar Coordinator Position (RC). That position sometimes referred to as “Coordinator,” “Tracker,” or “Handoff Controller” (En Route).
5. Radar Flight Data (FD). That position commonly referred to as “Assistant Controller” or “A-Side” position.
6. Nonradar Position (NR). That position which is usually in direct communication with the aircraft and which uses nonradar procedures as the primary means of separation.
c. Primary responsibilities of the En Route Sector Team Positions:
1. Radar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate automated handoffs.
(e) Assist the radar associate position with nonautomated handoff actions when needed.
(f) Assist the radar associate position in coordination when needed.
(g) Scan radar display. Correlate with flight progress strip information or User Request Evaluation Tool (URET) data, as applicable.
(h) Ensure computer entries are completed on instructions or clearances you issue or receive.
(i) Ensure strip marking and/or URET entries are completed on instructions or clearances you issue or receive.
(j) Adjust equipment at radar position to be usable by all members of the team.
(k) The radar controller shall not be responsible for G/G communications when precluded by VSCS split functionality.
2. Radar Associate Position:
(a) Ensure separation.
(b) At URET facilities, use URET information to plan, organize, and expedite the flow of traffic.
(c) Initiate control instructions.
(d) Operate interphones.
(e) Accept and initiate nonautomated handoffs,
and ensure radar position is made aware of the actions.
(f) Assist the radar position by accepting or initiating automated handoffs which are necessary for the continued smooth operation of the sector, and ensure that the radar position is made immediately aware of any action taken.
(g) Coordinate, including pointouts.
(h) Monitor radios when not performing higher priority duties.
(i) Scan flight progress strips and/or URET data. Correlate with radar data.
(j) Manage flight progress strips and/or URET flight data.
(k) Ensure computer entries are completed on instructions issued or received. Enter instructions issued or received by the radar position when aware of those instructions.
(l) As appropriate, ensure strip marking and/or URET entries are completed on instructions issued or received, and record instructions issued or received by the radar position when aware of them.
(m) Adjust equipment at radar associate position to be usable by all members of the team.
(n) Where authorized, perform URET data entries to keep the activation status of designated URET Airspace Configuration Elements current.
3. Radar Coordinator Position:
(a) Perform interfacility/intrafacility/sector/position coordination of traffic actions.
(b) Advise the radar position and the radar associate position of sector actions required to accomplish overall objectives.
(c) Perform any of the functions of the en route sector team which will assist in meeting situation objectives.
(d) The RC controller shall not be responsible for monitoring or operating radios when precluded by VSCS split functionality.
NOTE- The Radar Position has the responsibility for managing the overall sector operations, including aircraft separation and traffic flows. The Radar Coordinator Position assumes responsibility for managing traffic flows and the Radar Position retains responsibility for aircraft separation when the Radar Coordinator Position is staffed.
4. Radar Flight Data:
(a) Operate interphone.
(b) Assist Radar Associate Position in managing flight progress strips.
(c) Receive/process and distribute flight progress strips.
(d) Ensure flight data processing equipment is operational, except for URET capabilities.
(e) Request/receive and disseminate weather, NOTAMs, NAS status, traffic management, and Special Use Airspace status messages.
(f) Manually prepare flight progress strips when automation systems are not available.
(g) Enter flight data into computer.
(h) Forward flight data via computer.
(i) Assist facility/sector in meeting situation objectives.
5. En Route Nonradar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate transfer of control, communications, and flight data.
(e) Ensure computer entries are completed on instructions or clearances issued or received.
(f) Ensure strip marking is completed on instructions or clearances issued or received.
(g) Facilities utilizing nonradar positions may modify the standards contained in the radar associate, radar coordinator, and radar flight data sections to accommodate facility/sector needs, i.e., nonradar coordinator, nonradar data positions.
TERMINAL RADAR/NONRADAR TEAM POSITION RESPONSIBILITIES
a. Terminal Radar Team Concept and Intent:
1. There are no absolute divisions of responsibilities regarding position operations. The tasks to be completed remain the same whether one, two, or three people are working positions within a facility/sector. The team, as a whole, has responsibility for the safe and efficient operation of that facility/sector.
2. The intent of the team concept is not to hold the team accountable for the action of individual members in the event of an operational error/deviation.
b. Terms. The following terms will be used in terminal facilities for the purposes of standardization.
1. Facility/Sector. The area of control responsibility (delegated airspace) of the radar team, and the team as a whole.
2. Radar Position (R). That position which is in direct communication with the aircraft and which uses radar information as the primary means of separation.
3. Radar Associate Position (RA). That position commonly referred to as “Handoff Controller” or “Radar Data Controller.”
4. Radar Coordinator Position (RC). That position commonly referred to as “Coordinator,” “Tracker,” “Sequencer,” or “Overhead.”
5. Radar Flight Data (FD). That position commonly referred to as “Flight Data.”
6. Nonradar Position (NR). That position which is usually in direct communication with the aircraft and which uses nonradar procedures as the primary means of separation.
c. Primary Responsibilities of the Terminal Radar Team Positions:
1. Radar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate automated handoffs.
(e) Assist the Radar Associate Position with nonautomated handoff actions when needed.
(f) Assist the Radar Associate Position in coordination when needed.
(g) Scan radar display. Correlate with flight progress strip information.
(h) Ensure computer entries are completed on instructions or clearances you issue or receive.
(i) Ensure strip marking is completed on instructions or clearances you issue or receive.
(j) Adjust equipment at Radar Position to be usable by all members of the team.
2. Radar Associate Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Operate interphones.
(d) Maintain awareness of facility/sector activities.
(e) Accept and initiate nonautomated handoffs.
(f) Assist the Radar Position by accepting or initiating automated handoffs which are necessary for the continued smooth operation of the facility/sector and ensure that the Radar Position is made immediately aware of any actions taken.
(g) Coordinate, including point outs.
(h) Scan flight progress strips. Correlate with radar data.
(i) Manage flight progress strips.
(j) Ensure computer entries are completed on instructions issued or received, and enter instructions issued or received by the Radar Position when aware of those instructions.
(k) Ensure strip marking is completed on instructions issued or received, and write instructions issued or received by the Radar Position when aware of them.
(l) Adjust equipment at Radar Associate Position to be usable by all members of the Radar Team.
3. Radar Coordinator Position:
(a) Perform interfacility/sector/position coordination of traffic actions.
(b) Advise the Radar Position and the Radar Associate Position of facility/sector actions required to accomplish overall objectives.
(c) Perform any of the functions of the Radar Team which will assist in meeting situation objectives.
NOTE-The Radar Position has the responsibility of managing the overall sector operations, including aircraft separation and traffic flows. The Radar Coordinator Position assumes responsibility for managing traffic flows and the Radar Position retains responsibility for aircraft separation when the Radar Coordinator Position is staffed.
4. Radar Flight Data:
(a) Operate interphones.
(b) Process and forward flight plan information.
(c) Compile statistical data.
(d) Assist facility/sector in meeting situation objectives.
5. Terminal Nonradar Position:
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate radios.
(d) Accept and initiate transfer of control, communications and flight data.
(e) Ensure computer entries are completed on instructions or clearances issued or received.
(f) Ensure strip marking is completed on instructions or clearances issued or received.
(g) Facilities utilizing nonradar positions may modify the standards contained in the radar associate, radar coordinator, and radar flight data sections to accommodate facility/sector needs, i.e., nonradar coordinator, nonradar data positions.
TOWER TEAM POSITION RESPONSIBILITIES
a. Tower Team Concept and Intent:
1. There are no absolute divisions of responsibilities regarding position operations. The tasks to be completed remain the same whether one, two, or three people are working positions within a tower cab. The team as a whole has responsibility for the safe and efficient operation of that tower cab.
2. The intent of the team concept is not to hold the team accountable for the action of individual members in the event of an operational error/deviation.
b. Terms: The following terms will be used in terminal facilities for the purpose of standardization.
1. Tower Cab: The area of control responsibility (delegated airspace and/or airport surface areas) of the tower team, and the team as a whole.
2. Tower Position(s) (LC or GC): That position which is in direct communications with the aircraft and ensures separation of aircraft in/on the area of jurisdiction.
3. Tower Associate Position(s): That position commonly referred to as “Local Assist,” “Ground Assist,” “Local Associate,” or “Ground Associate.”
4. Tower Cab Coordinator Position (CC): That position commonly referred to as “Coordinator.”
5. Flight Data (FD): That position commonly referred to as “Flight Data.”
6. Clearance Delivery (CD): That position commonly referred to as “Clearance.”
c. Primary responsibilities of the Tower Team Positions:
1. Tower Position(s) (LC or GC):
(a) Ensure separation.
(b) Initiate control instructions.
(c) Monitor and operate communications equipment.
(d) Utilize tower radar display(s).
(e) Utilize alphanumerics.
(f) Assist the Tower Associate Position with coordination.
(g) Scan tower cab environment.
(h) Ensure computer entries are completed for instructions or clearances issued or received.
(i) Ensure strip marking is completed for instructions or clearances issued or received.
(j) Process and forward flight plan information.
(k) Perform any functions of the Tower Team which will assist in meeting situation objectives.
2. Tower Associate Position(s):
(a) Ensure separation.
(b) Operate interphones.
(c) Maintain awareness of tower cab activities.
(d) Utilize alphanumerics.
(e) Utilize tower radar display(s).
(f) Assist Tower Position by accepting/initiating coordination for the continued smooth operation of the tower cab and ensure that the Tower Position is made immediately aware of any actions taken.
(g) Manage flight plan information.
(h) Ensure computer entries are completed for instructions issued or received and enter instructions issued or received by a Tower Position.
(i) Ensure strip marking is completed for instructions issued or received and enter instructions issued or received by a Tower Position.
3. Tower Coordinator Position:
(a) Perform interfacility/position coordination for traffic actions.
(b) Advise the tower and the Tower Associate Position(s) of tower cab actions required to accomplish overall objectives.
(c) Perform any of the functions of the Tower Team which will assist in meeting situation objectives.
NOTE- The Tower Positions have the responsibility for aircraft separation and traffic flows. The Tower Coordinator Position assumes responsibility for managing traffic flows and the Tower Positions retain responsibility for aircraft separation when the Tower Coordinator Position is staffed.
4. Flight Data:
(a) Operate interphones.
(b) Process and forward flight plan information.
(c) Compile statistical data.
(d) Assist tower cab in meeting situation objectives.
(e) Observe and report weather information.
(f) Utilize alphanumerics.
5. Clearance Delivery:
(a) Operate communications equipment.
(b) Process and forward flight plan information.
(c) Issue clearances and ensure accuracy of pilot read back.
(d) Assist tower cab in meeting situation objectives.
(e) Operate tower equipment.
(f) Utilize alphanumerics.
NOTE-The Tower Positions have the responsibility for aircraft separation and traffic flows. The Tower Coordinator Position assumes responsibility for managing traffic flows and the Tower Positions retain responsibility for aircraft separation when the Tower Coordinator Position is staffed.
12
Airport Traffic Control- Terminal
PROVIDE SERVICE
Provide airport traffic control service based only upon observed or known traffic and airport conditions.
NOTE- When operating in accordance with CFRs, it is the responsibility of the pilot to avoid collision with other aircraft. However, due to the limited space around terminal locations, traffic information can aid pilots in avoiding collision between aircraft operating
within Class B, Class C, or Class D surface areas and the terminal radar service areas, and transiting aircraft operating in proximity to terminal locations.
PREVENTIVE CONTROL
Provide preventive control service only to aircraft operating in accordance with a letter of agreement. When providing this service, issue advice or instructions only if a situation develops which requires corrective action.
NOTE- Preventive control differs from other airport traffic control in that repetitious, routine approval of pilot action is eliminated. Controllers intervene only when they observe a traffic conflict developing.
USE OF ACTIVE RUNWAYS
The local controller has primary responsibility for
operations conducted on the active runway and must control the use of those runways. Positive coordination and control is required as follows:
NOTE- Exceptions may be authorized only as provided in Constraints Governing Supplements and Procedural Deviations, and FAAO JO 7210.3, Facility Operation and Administration, para 10-1-7, Use of Active Runways, where justified by extraordinary circumstances at specific locations.
a. Ground control must obtain approval from local control before authorizing an aircraft or a vehicle to cross or use any portion of an active runway. The coordination shall include the point/intersection at the runway where the operation will occur.
PHRASEOLOGY- CROSS (runway) AT (point/intersection).
b. When the local controller authorizes another controller to cross an active runway, the local controller shall verbally specify the runway to be crossed and the point/intersection at the runway where the operation will occur preceded by the word “cross.”
PHRASEOLOGY- CROSS (runway) AT (point/intersection).
c. The ground controller shall advise the local controller when the coordinated runway operation is complete. This may be accomplished verbally or through visual aids as specified by a facility directive.
d. USA/USAF/USN NOT APPLICABLE. Authorization for aircraft/vehicles to taxi/proceed on or along an active runway, for purposes other than crossing, shall be provided via direct communications on the appropriate local control frequency. This authorization may be provided on the ground control frequency after coordination with local control is completed for those operations specifically described in a facility directive.
NOTE- The USA, USAF, and USN establish local operating procedures in accordance with, respectively, USA, USAF, and USN directives.
e. The local controller shall coordinate with the ground controller before using a runway not previously designated as active.
COORDINATION BETWEEN LOCAL AND GROUND CONTROLLERS
Local and ground controllers shall exchange information as necessary for the safe and efficient use of airport runways and movement areas. This may be accomplished via verbal means, flight progress strips, other written information, or automation displays. As a minimum, provide aircraft identification and applicable runway/intersection/taxiway information as follows:
a. Ground control shall notify local control when a departing aircraft has been taxied to a runway other than one previously designated as active.
b. Ground control must notify local control of any aircraft taxied to an intersection for takeoff. This notification may be accomplished by verbal means or by flight progress strips.
c. When the runways in use for landing/departing aircraft are not visible from the tower or the aircraft using them are not visible on radar, advise the local/ground controller of the aircraft’s location before releasing the aircraft to the other controller.
VEHICLES/EQUIPMENT/PERSONNEL ON RUNWAYS
a. Ensure that the runway to be used is free of all known ground vehicles, equipment, and personnel before a departing aircraft starts takeoff or a landing aircraft crosses the runway threshold.
b. Vehicles, equipment, and personnel in direct communications with the control tower may be authorized to operate up to the edge of an active runway surface when necessary. Provide advisories as specified Traffic Information, Precision Approach Critical Area, as appropriate.
PHRASEOLOGY- PROCEED AS REQUESTED; AND IF NECESSARY, (additional instructions or information).
NOTE- Establishing hold lines/signs is the responsibility of the airport manager. Standards for surface measurements, markings,
and signs are contained in the following Advisory Circulars;
AC 150/5300-13, Airport Design; AC 150/5340-1, Standards for Airport Markings, and AC 150/5340-18, Standards for Airport Sign Systems. The operator is responsible to properly position the aircraft, vehicle, or equipment at the appropriate hold line/sign or designated point. The requirements in, Visually Scanning Runways, remain valid as appropriate.
TRAFFIC INFORMATION
a. Describe vehicles, equipment, or personnel on or near the movement area in a manner which will assist pilots in recognizing them.
EXAMPLE- “Mower left of runway two seven.”
“Trucks crossing approach end of runway two five.”
“Workman on taxiway Bravo.”
“Aircraft left of runway one eight.”
b. Describe the relative position of traffic in an easy to understand manner, such as “to your right” or “ahead of you.”
EXAMPLE- “Traffic, U.S. Air MD-Eighty on downwind leg to your left.”
“King Air inbound from outer marker on straight-in approach to runway one seven.”
c. When using a CTRD, you may issue traffic advisories using the standard radar phraseology prescribed in, Traffic Advisories.
POSITION DETERMINATION : Determine the position of an aircraft before issuing taxi instructions or takeoff clearance.
NOTE- The aircraft’s position may be determined visually by the controller, by pilots, or through the use of the ASDE.
LOW LEVEL WIND SHEAR/MICROBURST ADVISORIES
a. When low level wind shear/microburst is reported by pilots, Integrated Terminal Weather System (ITWS), or detected on wind shear detection systems such as LLWAS NE++, LLWAS-RS, WSP, or TDWR, controllers shall issue the alert to all arriving and departing aircraft. Continue the alert to aircraft until it is broadcast on the ATIS and pilots indicate they have received the appropriate ATIS code. A statement shall be included on the ATIS for 20 minutes following the last report or indication of the wind shear/microburst.
PHRASEOLOGY- LOW LEVEL WIND SHEAR (or MICROBURST, as appropriate) ADVISORIES IN EFFECT.
b. At facilities without ATIS, ensure that wind shear/microburst information is broadcast to all arriving and departing aircraft for 20 minutes following the last report or indication of wind shear/microburst.
1. At locations equipped with LLWAS, the local controller shall provide wind information as follows:
NOTE- The LLWAS is designed to detect low level wind shear conditions around the periphery of an airport. It does not detect wind shear beyond that limitation.
(a) If an alert is received, issue the airport wind and the displayed field boundary wind.
PHRASEOLOGY- WIND SHEAR ALERT. AIRPORT WIND (direction) AT (velocity). (Location of sensor) BOUNDARY WIND (direction) AT (velocity).
(b) If multiple alerts are received, issue an advisory that there are wind shear alerts in two/several/all quadrants. After issuing the advisory, issue the airport wind in accordance with para 3-9-1, Departure Information, followed by the field boundary wind most appropriate to the aircraft operation.
PHRASEOLOGY- WIND SHEAR ALERTS TWO/SEVERAL/ALL QUADRANTS. AIRPORT WIND (direction) AT (velocity). (Location of sensor) BOUNDARY WIND (direction) AT (velocity).
(c) If requested by the pilot, issue specific field boundary wind information even though the LLWAS may not be in alert status.
NOTE- The requirements for issuance of wind information remain valid as appropriate under this paragraph, Departure Information, Landing Information.
2. Wind shear detection systems, including TDWR, WSP, LLWAS NE++ and LLWAS-RS provide the capability of displaying microburst alerts, wind shear alerts, and wind information oriented to the threshold or departure end of a runway. When detected, the associated ribbon display allows the controller to read the displayed alert without any need for interpretation.
(a) If a wind shear or microburst alert is received for the runway in use, issue the alert information for that runway to arriving and departing aircraft as it is displayed on the ribbon display.
PHRASEOLOGY- (Runway) (arrival/departure) WIND SHEAR/MICROBURST ALERT, (windspeed) KNOT GAIN/LOSS, (location).
EXAMPLE- 17A MBA 40K - 3MF
PHRASEOLOGY- RUNWAY 17 ARRIVAL MICROBURST ALERT 40 KNOT LOSS 3 MILE FINAL.
EXAMPLE- 17D WSA 25K+ 2MD
PHRASEOLOGY- RUNWAY 17 DEPARTURE WIND SHEAR ALERT 25 KNOT GAIN 2 MILE DEPARTURE.
(b) If requested by the pilot or deemed appropriate by the controller, issue the displayed wind information oriented to the threshold or departure end of the runway.
PHRASEOLOGY- (Runway) DEPARTURE/THRESHOLD WIND (direction) AT (velocity).
(c) LLWAS NE++ or LLWAS-RS may detect a possible wind shear/microburst at the edge of the system but may be unable to distinguish between a wind shear and a microburst. A wind shear alert message will be displayed, followed by an asterisk, advising of a possible wind shear outside of the system network.
NOTE- LLWAS NE++ when associated with TDWR can detect wind shear/microbursts outside the network if the TDWR fails.
PHRASEOLOGY- (Appropriate wind or alert information) POSSIBLE WIND SHEAR OUTSIDE THE NETWORK.
(d) If unstable conditions produce multiple alerts, issue an advisory of multiple wind shear/microburst alerts followed by specific alert or wind information most appropriate to the aircraft operation.
PHRASEOLOGY- MULTIPLE WIND SHEAR/MICROBURST ALERTS (specific alert or wind information).
(e) The LLWAS NE++ and LLWAS-RS are designed to operate with as many as 50 percent of the total sensors inoperative. When all three remote sensors designated for a specific runway arrival or departure wind display line are inoperative then the LLWAS NE++ and LLWAS-RS for that runway arrival/departure shall be considered out of service. When a specific runway arrival or departure wind display line is inoperative and wind shear/microburst activity is likely; (e.g.; frontal activity, convective storms, PIREPs), a statement shall be included on the ATIS, “WIND SHEAR AND MICROBURST INFORMATION FOR RUNWAY (runway number) ARRIVAL/DEPARTURE NOT AVAILABLE.”
NOTE- The geographic situation display (GSD) is a supervisory planning tool and is not intended to be a primary tool for microburst or wind shear.
USE OF TOWER RADAR DISPLAYS
a. Uncertified tower display workstations shall be used only as an aid to assist controllers in visually locating aircraft or in determining their spacial relationship to known geographical points. Radar services and traffic advisories are not to be provided using uncertified tower display workstations. General information may be given in an easy to understand manner, such as “to your right” or “ahead of you.”
EXAMPLE- “Follow the aircraft ahead of you passing the river at the stacks.” “King Air passing left to right.”
b. Local controllers may use certified tower radar displays for the following purposes:
1. To determine an aircraft’s identification, exact location, or spatial relationship to other aircraft.
NOTE- This authorization does not alter visual separation procedures. When employing visual separation, the provisions of, Visual Separation, apply unless otherwise authorized by the Vice President of Terminal Service.
2. To provide aircraft with radar traffic advisories.
3. To provide a direction or suggested headings to VFR aircraft as a method for radar identification or as an advisory aid to navigation.
PHRASEOLOGY- (Identification), PROCEED (direction)-BOUND, (other instructions or information as necessary), or (identification), SUGGESTED HEADING (degrees), (other instructions as necessary).
NOTE- It is important that the pilot be aware of the fact that the directions or headings being provided are suggestions or are advisory in nature. This is to keep the pilot from being inadvertently misled into assuming that radar vectors (and other associated radar services) are being provided when, in fact, they are not.
4. To provide information and instructions to aircraft operating within the surface area for which the tower has responsibility.
EXAMPLE- “TURN BASE LEG NOW.”
NOTE- Unless otherwise authorized, tower radar displays are intended to be an aid to local controllers in meeting their responsibilities to the aircraft operating on the runways or within the surface area. They are not intended to provide radar benefits to pilots except for those accrued through a more efficient and effective local control position. In addition, local controllers at nonapproach control towers must devote the majority of their time to visually scanning the runways and local area; an assurance of continued positive radar identification could place distracting and operationally inefficient requirements upon the local controller. Therefore, since the requirements of para 5-3-1, Application, cannot be assured, the radar functions prescribed above are not considered to be radar services and pilots should not be advised of being in “radar contact.”
c. Additional functions may be performed provided the procedures have been reviewed and authorized by appropriate management levels.
OBSERVED ABNORMALITIES
When requested by a pilot or when you deem it necessary, inform an aircraft of any observed abnormal aircraft condition.
PHRASEOLOGY- (Item) APPEAR/S (observed condition).
EXAMPLE- “Landing gear appears up.”
“Landing gear appears down and in place.”
“Rear baggage door appears open.”
SURFACE AREA RESTRICTIONS
a. If traffic conditions permit, approve a pilot’s request to cross Class C or Class D surface areas or exceed the Class C or Class D airspace speed limit. Do not, however, approve a speed in excess of 250 knots (288 mph) unless the pilot informs you a higher minimum speed is required.
NOTE- 14 CFR Section 91.117 permits speeds in excess of 250 knots (288 mph) when so required or recommended in the airplane flight manual or required by normal military operating procedures.
b. Do not approve a pilot’s request or ask a pilot to conduct unusual maneuvers within surface areas of Class B, C, or D airspace if they are not essential to the performance of the flight.
EXCEPTION. A pilot’s request to conduct aerobatic practice activities may be approved, when operating in accordance with a letter of agreement, and the activity will have no adverse effect on safety of the air traffic operation or result in a reduction of service to other users.
NOTE- These unusual maneuvers include unnecessary low passes, unscheduled flybys, practice instrument approaches to altitudes below specified minima (unless a landing or
touch-and-go is to be made), or any so-called “buzz jobs”
wherein a flight is conducted at a low altitude and/or a
high rate of speed for thrill purposes. Such maneuvers increase hazards to persons and property and contribute to noise complaints.
VISUALLY SCANNING RUNWAYS
a. Local controllers shall visually scan runways to the maximum extent possible.
b. Ground control shall assist local control in visually scanning runways, especially when runways are in close proximity to other movement areas.
ESTABLISHING TWO-WAY COMMUNICATIONS
Pilots are required to establish two-way radio communications before entering the Class D airspace. If the controller responds to a radio call with, “(a/c call sign) standby,” radio communications have been established and the pilot can enter the Class D
airspace. If workload or traffic conditions prevent immediate provision of Class D services, inform the pilot to remain outside the Class D airspace until conditions permit the services to be provided.
PHRASEOLOGY- (A/c call sign) REMAIN OUTSIDE DELTA AIRSPACE AND STANDBY.
GROUND OPERATIONS WHEN VOLCANIC ASH IS PRESENT
When volcanic ash is present on the airport surface, and to the extent possible:
a. Avoid requiring aircraft to come to a full stop while taxiing.
b. Provide for a rolling takeoff for all departures.
NOTE- When aircraft begin a taxi or takeoff roll on ash contaminated surfaces, large amounts of volcanic ash will again become airborne. This newly airborne ash will significantly reduce visibility and will be ingested by the engines of following aircraft.
Visual Signals
LIGHT SIGNALS : Use ATC light signals control aircraft and the movement of vehicles, equipment, and personnel on the movement area when radio communications cannot be employed.
WARNING SIGNAL : Direct a general warning signal, alternating red and green, to aircraft or vehicle operators, as appropriate, when:
NOTE- The warning signal is not a prohibitive signal and can be followed by any other light signal, as circumstances permit.
a. Aircraft are converging and a collision hazard exists.
b. Mechanical trouble exists of which the pilot might not be aware.
c. Other hazardous conditions are present which call for intensified pilot or operator alertness. These conditions may include obstructions, soft field, ice on the runway, etc.
RECEIVER-ONLY ACKNOWLEDGMENT
To obtain acknowledgment from an aircraft equipped with receiver only, request the aircraft to do the following:
a. Fixed-wing aircraft:
1. Between sunrise and sunset:
(a) Move ailerons or rudders while on the ground.
(b) Rock wings while in flight.
2. Between sunset and sunrise: Flash navigation or landing lights.
b. Helicopters:
1. Between sunrise and sunset:
(a) While hovering, either turn the helicopter toward the controlling facility and flash the landing light or rock the tip path plane.
(b) While in flight, either flash the landing light or rock the tip path plane.
2. Between sunset and sunrise: Flash landing light or search light.
ATC Light Signals
Airport Conditions
LANDING AREA CONDITIONIf you observe or are informed of any condition which affects the safe use of a landing area:
NOTE- 1. The airport management/military operations office is responsible for observing and reporting the condition of the landing area. 2. It is the responsibility of the agency operating the airport to provide the tower with current information regarding airport conditions. 3. A disabled aircraft on a runway, after occupants are clear, is normally handled by flight standards and airport management/military operations office personnel in the same manner as any obstruction; e.g., construction equipment.
- Relay the information to the airport manager/military operations office concerned.
- Copy verbatim any information received and record the name of the person submitting it.
- Confirm information obtained from other than authorized airport or FAA personnel unless this function is the responsibility of the military operations office.
NOTE- Civil airport managers are required to provide a list of airport employees who are authorized to issue information concerning conditions affecting the safe use of the airport.
- If you are unable to contact the airport management or operator, issue a NOTAM publicizing an unsafe condition and inform the management or operator as soon as practicable.
EXAMPLE- “DISABLED AIRCRAFT ON RUNWAY.’’
NOTE- 1. Legally, only the airport management/military operations office can close a runway. 2. Military controllers are not authorized to issue NOTAMs. It is the responsibility of the military operations office.
- Issue to aircraft only factual information, as reported by the airport management concerning the condition of the runway surface, describing the accumulation of precipitation.
EXAMPLE- “ALL RUNWAYS COVERED BY COMPACTED SNOW SIX INCHES DEEP.”
CLOSED/UNSAFE RUNWAY INFORMATION
If an aircraft requests to takeoff, land, or touch-and-go on a closed or unsafe runway, inform the pilot the runway is closed or unsafe, and
- The pilot persists in his/her request, quote him/her the appropriate parts of the NOTAM applying to the runway and inform him/her that a clearance cannot be issued.
- Then, if the pilot insists and in your opinion the intended operation would not adversely affect other traffic, inform him/her that the operation will be at his/her own risk.
PHRASEOLOGY- RUNWAY (runway number) CLOSED/UNSAFE.
If appropriate, (quote NOTAM information), UNABLE TO ISSUE DEPARTURE/LANDING/TOUCH-AND-GO CLEARANCE. DEPARTURE/LANDING/TOUCH-AND-GO WILL BE AT YOUR OWN RISK.
c. Except as permitted, Side-step Maneuver, where parallel runways are served by separate ILS/MLS systems and one of the runways is closed, the ILS/MLS associated with the closed runway should not be used for approaches unless not using the ILS/MLS would have an adverse impact on the operational efficiency of the airport.
TIMELY INFORMATION: Issue airport condition information necessary for an aircraft’s safe operation in time for it to be useful to the pilot. Include the following, as appropriate:
a. Construction work on or immediately adjacent to the movement area.
b. Rough portions of the movement area.
c. Braking conditions caused by ice, snow, slush, or water.
d. Snowdrifts or piles of snow on or along the edges of the area and the extent of any plowed area.
e. Parked aircraft on the movement area.
f. Irregular operation of part or all of the airport lighting system.
g. Volcanic ash on any airport surface area and whether the ash is wet or dry (if known).
NOTE- Braking action on wet ash may be degraded. Dry ash on the runway may necessitate minimum use of reverse thrust.
h. Other pertinent airport conditions.
BRAKING ACTION
Furnish quality of braking action, as received from pilots or the airport management, to all aircraft as follows:
a. Describe the quality of braking action using the terms “good,” “fair,” “poor,” “nil,” or a combination of these terms. If the pilot or airport management reports braking action in other than the foregoing terms, ask him/her to categorize braking action in these terms.
NOTE- The term “nil” is used to indicate bad or no braking action.
b. Include type of aircraft or vehicle from which the report is received.
EXAMPLE- “Braking action fair to poor, reported by a heavy D-C Ten.”
“Braking action poor, reported by a Boeing Seven Twenty-Seven.”
c. If the braking action report affects only a portion of a runway, obtain enough information from the pilot or airport management to describe the braking action in terms easily understood by the pilot.
EXAMPLE- “Braking action poor first half of runway, reported by a Lockheed Ten Eleven.”
“Braking action poor beyond the intersection of runway two seven, reported by a Boeing Seven Twenty-Seven.”
NOTE- Descriptive terms, such as the first or the last half of the runway, should normally be used rather than landmark descriptions, such as opposite the fire station, south of a taxiway, etc. Landmarks extraneous to the landing runway are difficult to distinguish during low visibility, at night, or anytime a pilot is busy landing an aircraft.
d. Furnish runway friction measurement readings/values as received from airport management to aircraft as follows:
1. Furnish information as received from the airport management to pilots on the ATIS at locations where friction measuring devices, such as MU-Meter, Saab Friction Tester (SFT), and Skiddometer are in use only when the MU values are 40 or less. Use the runway followed by the MU number for each of the three runway segments, time of report, and a word describing the cause of the runway friction problem. Do not issue MU values when all three segments of the runway have values reported greater than 40.
EXAMPLE- “Runway two seven, MU forty-two, forty-one, twenty-eight at one zero one eight Zulu, ice.”
2. Issue the runway surface condition and/or the Runway Condition Reading (RCR), if provided, to all USAF and ANG aircraft. Issue the RCR to other aircraft upon pilot request.
EXAMPLE- “Ice on runway, RCR zero five, patchy.”
NOTE- 1. USAF has established RCR procedures for determining the average deceleration readings of runways under conditions of water, slush, ice, or snow. The use of the RCR code is dependent upon the pilot’s having a “stopping capability chart” specifically applicable to his/her aircraft. 2. USAF offices furnish RCR information at airports serving USAF and ANG aircraft.
BRAKING ACTION ADVISORIES
a. When runway braking action reports are received from pilots or the airport management which include the terms “fair,” “poor,” or “nil” or whenever weather conditions are conducive to deteriorating or rapidly changing runway conditions, include on the ATIS broadcast the statement “Braking Action Advisories are in effect.”
b. During the time Braking Action Advisories are in effect, take the following action:
1. Issue the latest braking action report for the runway in use to each arriving and departing aircraft early enough to be of benefit to the pilot. When possible, include reports from heavy jet aircraft when the arriving or departing aircraft is a heavy jet.
2. If no report has been received for the runway of intended use, issue an advisory to that effect.
PHRASEOLOGY- NO BRAKING ACTION REPORTS RECEIVED FOR RUNWAY (runway number).
3. Advise the airport management that runway braking action reports of “fair,” “poor,” or “nil” have been received.
4. Solicit PIREPs of runway braking action.
c. Include runway friction measurement/values received from airport management on the ATIS. Furnish the information when requested by the pilot in accordance with para 3-3-4, Braking Action.
ARRESTING SYSTEM OPERATION
a. For normal operations, arresting systems remotely controlled by ATC shall remain in the retracted or down position.
NOTE- 1. USN- Runway Arresting Gear- barriers are not operated by ATC personnel. Readiness/rigging of the equipment is the responsibility of the operations department. 2. A request to raise a barrier or hook cable means the barrier or cable on the departure end of the runway. If an approach end engagement is required, the pilot or military authority will specifically request that the approach end cable be raised.
b. Raise aircraft arresting systems whenever:
1. Requested by a pilot.
NOTE- The standard emergency phraseology for a pilot requesting an arresting system to be raised for immediate engagement is: “BARRIER - BARRIER - BARRIER” or “CABLE - CABLE - CABLE.”
2. Requested by military authority; e.g., airfield manager, supervisor of flying, mobile control officer, etc.
NOTE- USAF. Web barriers at the departure end of the runway may remain in the up position when requested by the senior operational commander. The IFR Enroute Supplement and AP-1 will describe specific barrier configuration. ATC will advise transient aircraft of the barrier configuration using the phraseology in subpara c, below.
3. A military jet aircraft is landing with known or suspected radio failure or conditions (drag chute/hydraulic/electrical failure, etc.) that indicate an arresting system may be needed. Exceptions are authorized for military aircraft which cannot engage an arresting system (C-9, C-141, C-5, T-39, etc.) and should be identified in a letter of agreement and/or appropriate military directive.
c. When requested by military authority due to freezing weather conditions or malfunction of the activating mechanism, the barrier/cable may remain in a raised position provided aircraft are advised.
PHRASEOLOGY- YOUR DEPARTURE/LANDING WILL BE TOWARD/OVER A RAISED BARRIER/CABLE ON RUNWAY (number), (location, distance, as appropriate).
d. Inform civil and U.S. Army aircraft whenever rubber supported cables are in place at the approach end of the landing runway, and include the distance of the cables from the threshold. This information may be omitted if it is published in the “Notices to Airmen” publication/DOD FLIP.
EXAMPLE- “Runway One Four arresting cable one thousand feet from threshold.”
e. When arresting system operation has been requested, inform the pilot of the indicated barrier/cable
position.
PHRASEOLOGY- (Identification), BARRIER/CABLE INDICATES UP/DOWN. CLEARED FOR TAKEOFF/TO LAND.
f. Time permitting, advise pilots of the availability of all arresting systems on the runway in question when a pilot requests barrier information.
g. If an aircraft engages a raised barrier/cable, initiate crash alarm procedures immediately.
h. For preplanned practice engagements not associated with emergencies, crash alarm systems need not be activated if, in accordance with local military operating procedures, all required notifications are made before the practice engagement.
FAR FIELD MONITOR (FFM) REMOTE STATUS UNIT
a. Background.
1. To meet the demand for more facilities capable of operating under CAT III weather, Type II equipment is being upgraded to Integrity Level 3. This integrity level will support operations which place a high degree of reliance on ILS guidance for positioning through touchdown.
2. Installation of the FFM remote status indicating units is necessary to attain the integrity necessary to meet internationally agreed upon reliability values in support of CAT III operations on Type II ILS equipment. The remote status indicating unit used in conjunction with Type II equipment adds a third integrity test; thereby, producing an approach aid which has integrity capable of providing Level 3 service.
3. The remote status sensing unit, when installed in the tower cab, will give immediate indications of localizer out-of-tolerance conditions. The alarm in the FFM remote status sensing unit indicates an inoperative or an out-of-tolerance localizer signal; e.g., the
course may have shifted due to equipment
malfunction or vehicle/aircraft encroachment into the critical area.
b. Procedures.
1. Operation of the FFM remote sensing unit will be based on the prevailing weather. The FFM remote sensing unit shall be operational when the weather is below CAT I ILS minimums.
2. When the weather is less than that required for CAT I operations, the GRN-27 FFM remote status sensing unit shall be set at:
(a) “CAT II” when the RVR is less than 2,400 feet.
(b) “CAT III” when the RVR is less than 1,200 feet.
3. When the remote status unit indicates that the localizer FFM is in alarm (aural warning following the preset delay) and:
(a) The aircraft is outside the middle marker (MM), check for encroachment those portions of the critical area that can be seen from the tower. It is understood that the entire critical area may not be visible due to low ceilings and poor visibility. The check is strictly to determine possible causal factors for the out-of-tolerance situation. If the alarm has not cleared prior to the aircraft’s arriving at the MM, immediately issue an advisory that the FFM remote status sensing unit indicates the localizer is unreliable.
(b) The aircraft is between the MM and the inner marker (IM), immediately issue an advisory that the FFM remote status sensing unit indicates the localizer is unreliable.
PHRASEOLOGY- CAUTION, MONITOR INDICATES RUNWAY (number) LOCALIZER UNRELIABLE.
(c) The aircraft has passed the IM, there is no action requirement. Although the FFM has been modified with filters which dampen the effect of false alarms, you may expect alarms when aircraft are located between the FFM and the localizer antenna either on landing or on takeoff.
Airport Lighting
EMERGENCY LIGHTING: Whenever you become
aware that an emergency has or will occur, take action to
provide for the operation of all appropriate airport lighting aids as required.
RUNWAY END IDENTIFIER LIGHTS : When separate on-off controls are provided, operate runway end identifier lights:
a. When the associated runway lights are lighted. Turn the REIL off after:
1. An arriving aircraft has landed.
2. A departing aircraft has left the traffic pattern area.
3. It is determined that the lights are of no further use to the pilot.
b. As required by facility directives to meet local conditions.
c. As requested by the pilot.
HELICOPTER LANDING CLEARANCE
a. Issue landing clearance for helicopters to movement areas other than active runways, or from diverse directions to points on active runways, with additional instructions, as necessary. Whenever possible, issue landing clearance in lieu of extended hover-taxi or air-taxi operations.
PHRASEOLOGY- MAKE APPROACH STRAIGHT-IN/CIRCLING LEFT/RIGHT TURN TO (location, runway, taxiway, helipad, Maltese cross) ARRIVAL/ARRIVAL ROUTE (number, name, or code).
HOLD SHORT OF (active runway, extended runway centerline, other).
REMAIN (direction/distance; e.g., 700 feet, 1 1/2 miles) FROM (runway, runway centerline, other helicopter/aircraft).
CAUTION (power lines, unlighted obstructions, wake turbulence, etc.).
CLEARED TO LAND.
CONTACT GROUND.
AIR TAXI TO RAMP.
b. If landing is requested to nonmovement areas and, in your judgment, the operation appears to be reasonable, use the following phraseology instead of the landing clearance in subpara a above.
PHRASEOLOGY- PROCEED AS REQUESTED, USE CAUTION (reason and additional instructions, as appropriate).
c. If landing is requested to an area not visible, an area not authorized for helicopter use, an unlighted nonmovement area at night, or an area off the airport, and traffic is not a factor, use the following phraseology.
PHRASEOLOGY- LANDING AT (requested location) WILL BE AT YOUR OWN RISK (reason and additional instructions, as necessary).
TRAFFIC (as applicable), or TRAFFIC NOT A FACTOR.
d. Unless requested by the pilot, do not issue downwind landings if the tailwind exceeds 5 knots.
NOTE- A pilot request to land at a given point from a given direction constitutes such a request.
Sea Lane Operations
APPLICATION : Where sea lanes are established and controlled, apply the provisions of this section.
DEPARTURE SEPARATION : Separate a departing aircraft from a preceding departing or arriving aircraft using the same sea lane by ensuring that it does not commence takeoff until:
a. The other aircraft has departed and crossed the end of the sea lane or turned to avert any conflict. If you can determine distances by reference to suitable landmarks, the other aircraft need only be airborne if the following minimum distance exists between aircraft:
1. When only Category I aircraft are involved- 1,500 feet.
2. When a Category I aircraft is preceded by a Category II aircraft- 3,000 feet.
3. When either the succeeding or both are Category II aircraft- 3,000 feet.
4. When either is a Category III aircraft- 6,000 feet.
b. A preceding landing aircraft has taxied out of the sea lane.
NOTE- Due to the absence of braking capability, caution should be exercised when instructing a float plane to hold a position as the aircraft will continue to move because of prop generated thrust. Clearance to taxi into position and hold should, therefore, be followed by takeoff or other clearance as soon as practicable.
ARRIVAL SEPARATION
Separate an arriving aircraft from another aircraft using
the same sea lane by ensuring that the arriving aircraft does not cross the landing threshold until one of the following conditions exists:
a. The other aircraft has landed and taxied out of the sea lane. Between sunrise and sunset, if you can determine distances by reference to suitable landmarks and the other aircraft has landed, it need not be clear of the sea lane if the following minimum distance from the landing threshold exists:
1. When a Category I aircraft is landing behind a Category I or II- 2,000 feet.
2. When a Category II aircraft is landing behind a Category I or II- 2,500 feet.
b. The other aircraft has departed and crossed the end of the sea lane or turned to avert any conflict. If you can determine distances by reference to suitable landmarks and the other aircraft is airborne, it need not have crossed the end of the sea lane if the following minimum distance from the landing threshold exists:
1. When only Category I aircraft are involved- 1,500 feet.
2. When either is a Category II aircraft- 3,000 feet.
3. When either is a Category III aircraft- 6,000 feet.
Glossary and Abbreviations
automatic dependent surveillance. A computer on board the plane uses the Global Positioning System to determine its position. It then sends this information regularly via satellite or a VHF (very high frequency) radio link to the Australian Advanced Air Traffic System, which then plots the aircraft’s position on the controller’s screen. This surveillance is used when an aircraft is out of radar range. Not all aircraft currently have this facility, but it seems likely that it will be installed on most international passenger aircraft.electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
flight data processing. This plots an aircraft’s expected position as calculated by computer from the aircraft flight plan (stored electronically by the Australian Advanced Air Traffic System).
frequency. A measure of how frequently an electromagnetic wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA).
Global Positioning System. The Global Positioning System (GPS) is a collection of 24 earth-orbiting satellites which allows any person who owns a GPS receiver to determine their location on the planet. More information on the Global Positioning System can be found How a GPS receiver works (How Stuff Works, USA) and The Global Positioning System: The role of atomic clocks (Beyond Discovery, National Academy of Sciences, USA).
radar. The use of reflected radio waves to determine the location of an object and its speed if it is moving. It is an acronym derived from radio detecting and ranging. For more information see How radar works (How Stuff Works, USA).
radio frequency. This is lowest of the electromagnetic radiation frequencies. Radio frequencies, or radio waves, have wavelengths ranging from less than a centimetre to as long as 100 kilometres. (See also electromagnetic radiation).
We divide the radio wave part of the electromagnetic spectrum into bands that are allocated to different uses. These include AM (amplitude modulation), FM (frequency modulation) and CB (citizens’ band) radio, television, aircraft communications, satellites, mobile phones and pagers. Within each band, no two transmissions can use the same part of the spectrum – or frequency - at the same time. For this reason, each band within the radio wave spectrum, itself a part of the broader electromagnetic spectrum, must be managed carefully to ensure the best use of this limited resource. For more information see How the radio spectrum works (How Stuff Works, USA).
VHF (very high frequency) radio. Radios that use frequencies in the range 30 to 300 megahertz (millions of oscillations per second). The wave length of these VHF radio waves range from 1 metre to 10 metres.
As used in this manual, the following abbreviations have the meanings indicated.
FAA Order JO 7110.65 Abbreviations
Abbreviation Meaning
AAR Airport acceptance rate
AC Advisory Circular
ACC Area Control Center
ACD ARTS Color Display
ACE-IDS ASOS Controller Equipment- Information Display System
ACL Aircraft list
ACLS Automatic Carrier Landing System
ADC Aerospace Defense Command
ADIZ Air Defense Identification Zone (to be pronounced “AY DIZ”)
ADS Automatic Dependent Surveillance
ADS-B Automatic Dependent Surveillance Broadcast
ADS-C Automatic Dependent Surveillance Contract
AFP Airspace Flow Program
AFSS Automated Flight Service Station
AIDC ATS Interfacility Data Communications
AIM Aeronautical Information Manual
AIRMET Airmen’s meteorological information
ALERFA Alert phase code (Alerting Service)
ALNOT Alert notice
ALS Approach Light System
ALTRV Altitude reservation
AMASS Airport Movement Area Safety System
AMB Ambiguity-A disparity greater than 2 miles exists between the position declared for a target by ATTS and another facility’s computer declared position during interfacility handoff
AMVER Automated Mutual Assistance Vessel Rescue System
ANG Air National Guard
APR ATC preferred route
APREQ Approval Request
ARINC Aeronautical Radio Incorporated
ARIP Air refueling initial point
ARSR Air route surveillance radar
ARTCC Air Route Traffic Control Center
ARTS Automated Radar Terminal System
ASD Aircraft Situation Display
ASDE Airport surface detection equipment
ASDE-X Airport Surface Detection Equipment System - Model X
ASF Airport Stream Filters
ASOS Automated Surface Observing System
ASR Airport surveillance radar
ATC Air traffic control
ATCAA ATC assigned airspace
ATCSCC David J. Hurley Air Traffic Control System Command Center
ATD Along-Track Distance
ATIS Automatic Terminal Information Service
ATO Air Traffic Organization
ATO COO Air Traffic Organization Chief Operating Officer
ATS Air Traffic Service
AWOS Automated Weather Observing System
BASE Cloud base
CA Conflict Alert
CARCAH Chief, Aerial Reconnaissance Coordination, All Hurricanes
CARF Central Altitude Reservation Function
CARTS Common ARTS
CAT Clear air turbulence
CDT Controlled departure time
CENRAP Center Radar ARTS Presentation
CEP Central East Pacific
CERAP Combined Center/RAPCON
CFR Code of Federal Regulations
CIC Controller-in-Charge
CNS Continuous
CPDLC Controller Pilot Data Link Communications
CPME Calibration Performance Monitor Equipment
CTA Control Area
CTRD Certified Tower Radar Display
CVFP Charted Visual Flight Procedure
CWA Center Weather Advisory
DARC Direct Access Radar Channel
DETRESFA Distress Phase code (Alerting Service)
DF Direction finder
DH Decision height
DL Departure List
DME Distance measuring equipment compatible with TACAN
DOE Department of Energy
DP Instrument Departure Procedure
DR Dead reckoning
DRT Diversion recovery tool
DSR Display System Replacement
DTAS Digital Terminal Automation Systems
DTM Digital Terrain Map
DVFR Defense Visual Flight Rules
DVRSN Diversion
EA Electronic Attack
EAS En Route Automation System
EDCT Expect Departure Clearance Time
EFC Expect further clearance
ELP Emergency Landing Pattern
ELT Emergency locator transmitter
EOS End Service
EOVM Emergency obstruction video map
ERIDS En Route Information Display System
ETA Estimated time of arrival
ETMS Enhanced Traffic Management System
FAA Federal Aviation Administration
FAAO FAA Order
FANS Future Air Navigation System
FDIO Flight Data Input/Output
FDP Flight data processing
FIR Flight Information Region
FL Flight level
FLIP Flight Information Publication
FLM Front-Line Manager
FLY Fly or flying
FMS Flight Management System
FMSP Flight Management System Procedure
FSM Flight Schedule Monitor
FSS Flight Service Station
GCA Ground controlled approach
GNSS Global Navigation Satellite System
GPD Graphics Plan Display
GPS Global Positioning System
GS Ground stop
HAR High Altitude Redesign
HERT Host Embedded Route Text
HF/RO High Frequency/Radio Operator
HIRL High intensity runway lights
IAFDOF Inappropriate Altitude for Direction of Flight
ICAO International Civil Aviation Organization
IDENT Aircraft identification
IDS Information Display System
IFR Instrument flight rules
IFSS International Flight Service Station
ILS Instrument Landing System
INCERFA Uncertainty Phase code (Alerting Service)
INREQ Information request
INS Inertial Navigation System
IR IFR military training route
IRU Inertial Reference Unit
ITWS Integrated Terminal Weather System
JATO Jet assisted takeoff
LAHSO Land and Hold Short Operations
LOA Letter of Agreement
LLWAS Low Level Wind Shear Alert System
LLWAS NE Low Level Wind Shear Alert System Network Expansion
LLWAS-RS Low Level Wind Shear Alert System Relocation/Sustainment
LLWS Low Level Wind Shear
L/MF Low/medium frequency
LORAN Long Range Navigation System
Mach Mach number
MALS Medium Intensity Approach Light System
MALSR Medium Approach Light System with runway alignment indicator lights
MAP Missed approach point
MARSA Military authority assumes responsibility for separation of aircraft
MCA Minimum crossing altitude
MCI Mode C Intruder
MDA Minimum descent altitude
MDM Main display monitor
MEA Minimum en route (IFR) altitude
MEARTS Micro En Route Automated Radar Tracking System
METAR Aviation Routine Weather Report
MIA Minimum IFR altitude
MIAWS Medium Intensity Airport Weather System
MIRL Medium intensity runway lights
MLS Microwave Landing System
MNPS Minimum Navigation Performance Specification
MNT Mach Number Technique
MOA Military operations area
MOCA Minimum obstruction clearance altitude
MRA Minimum reception altitude
MSAW Minimum Safe Altitude Warning
MSL Mean sea level
MTI Moving target indicator
MTR Military training route
MVA Minimum vectoring altitude
NADIN National Airspace Data Interchange Network
NAR National Automation Request
NAS National Airspace System
NAT ICAO North Atlantic Region
NBCAP National Beacon Code Allocation Plan
NDB Nondirectional radio beacon
NHOP National Hurricane Operations Plan
NIDS National Institute for Discovery Sciences
NM Nautical mile
NOAA National Oceanic and Atmospheric Administration
NOPAC North Pacific
NORAD North American Aerospace Defense Command
NOS National Ocean Service
NOTAM Notice to Airmen
NRP North American Route Program
NRR Nonrestrictive Route
NRS Navigation Reference System
NTZ No transgression zone
NWS National Weather Service
NWSOP National Winter Storm Operations Plan
ODALS Omnidirectional Approach Lighting System
ODP Obstacle Departure Procedure
OID Operator Interface Device
ONER Oceanic Navigational Error Report
OS Operations Supervisor
OTR Oceanic transition route
PAPI Precision Approach Path Indicators
PAR Precision approach radar
PAR Preferred arrival route
PBCT Proposed boundary crossing time
P/CG Pilot/Controller Glossary
PDAR Preferential departure arrival route
PDC Pre-Departure Clearance
PDR Preferential departure route
PIDP Programmable indicator data processor
PPI Plan position indicator
PTP Point-to-point
PVD Plan view display
RA Radar Associate
RAIL Runway alignment indicator lights
RAPCON Radar Approach Control Facility (USAF)
RATCF Radar Air Traffic Control Facility (USN)
RBS Radar bomb scoring
RCC Rescue Coordination Center
RCLS Runway Centerline System
RCR Runway condition reading
RDP Radar data processing
RE Recent (used to qualify weather phenomena such as rain, e.g. recent rain = RERA)
REIL Runway end identifier lights
RNAV Area navigation
RNP Required Navigation Performance
RTQC Real-Time Quality Control
RVR Runway visual range
RVSM Reduced Vertical Separation Minimum
RVV Runway visibility value
SAA Special Activity Airspace
SAR Search and rescue
SATCOM Satellite Communication
SELCAL Selective Calling System
SFA Single frequency approach
SFO Simulated flameout
SID Standard Instrument Departure
SIGMET Significant meteorological information
SPA Special Posting Area
SPECI Nonroutine (Special) Aviation Weather Report
STAR Standard terminal arrival
STARS Standard Terminal Automation Replacement System
STMC Supervisory Traffic Management Coordinator
STMCIC Supervisory Traffic Management Coordinator-in-charge
STOL Short takeoff and landing
SURPIC Surface Picture
SVFR Special Visual Flight Rules
TAA Terminal arrival area
TAS Terminal Automation Systems
TACAN TACAN UHF navigational aid (omnidirectional course and distance information)
TAWS Terrain Awareness Warning System
TCAS Traffic Alert and Collision Avoidance System
TCDD Tower cab digital display
TDLS Terminal Data Link System
TDW Tower display workstation
TDWR Terminal Doppler Weather Radar
TDZL Touchdown Zone Light System
TMC Traffic Management Coordinator
TMU Traffic Management Unit
TRACON Terminal Radar Approach Control
TRSA Terminal radar service area
UFO Unidentified flying object
UHF Ultra high frequency
URET User request evaluation tool
USA United States Army
USAF United States Air Force
USN United States Navy
UTC Coordinated universal time
UTM Unsuccessful transmission message
UUA Urgent pilot weather report
VFR Visual flight rules
VHF Very high frequency
VMC Visual meteorological conditions
VNAV Vertical Navigation
VOR VHF navigational aid (omnidirectional course information)
VOR/DME Collocated VOR and DME navigational aids (VHF course and UHF distance information)
VORTAC Collocated VOR and TACAN navigation aids (VHF and UHF course and UHF distance information)
VR VFR military training route
VSCS Voice Switching and Control System
WAAS Wide Area Augmentation System
WARP Weather and Radar Processing
WATRS West Atlantic Route System
WSO Weather Service Office
WSP Weather System Processor
WST Convective SIGMET
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