Summary

The nation's air traffic control system is responsible for managing a complex mixture of air traffic from commercial, general, corporate, and military aviation. Despite the strong safety record achieved over the last several decades, the system does suffer occasional serious disruption, often the result of outdated and failed equipment. When equipment failures occur, the safety of passengers and airplanes depends entirely on the skills of controllers and pilots.

Pressures to increase the number of flights that can be moved through the national airspace system safely and efficiently have led to proposals to provide more reliable and powerful equipment and at the same time increase the level of automation in air traffic control facilities—that is, to use advances in technology to take over tasks that are currently performed by humans. Such proposals have raised concern that automation may compromise the safety of the system by marginalizing the human controller's ability to provide the necessary backup when disruptions occur.

A second concern revolves around current planning toward a concept in which pilots, airline dispatchers, and managers assume more authority for air traffic control. This concept, referred to as free flight, has many implications for the controller's performance that parallel the implications of high levels of automation.

The Panel on Human Factors in Air Traffic Control Automation was convened at the request of the Federal Aviation Administration (FAA) to study the air traffic control system, the national airspace system, and future automation alternatives from a human factors perspective. The central premise of the analysis



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The Future of Air Traffic Control: Human Operators and Automation Summary The nation's air traffic control system is responsible for managing a complex mixture of air traffic from commercial, general, corporate, and military aviation. Despite the strong safety record achieved over the last several decades, the system does suffer occasional serious disruption, often the result of outdated and failed equipment. When equipment failures occur, the safety of passengers and airplanes depends entirely on the skills of controllers and pilots. Pressures to increase the number of flights that can be moved through the national airspace system safely and efficiently have led to proposals to provide more reliable and powerful equipment and at the same time increase the level of automation in air traffic control facilities—that is, to use advances in technology to take over tasks that are currently performed by humans. Such proposals have raised concern that automation may compromise the safety of the system by marginalizing the human controller's ability to provide the necessary backup when disruptions occur. A second concern revolves around current planning toward a concept in which pilots, airline dispatchers, and managers assume more authority for air traffic control. This concept, referred to as free flight, has many implications for the controller's performance that parallel the implications of high levels of automation. The Panel on Human Factors in Air Traffic Control Automation was convened at the request of the Federal Aviation Administration (FAA) to study the air traffic control system, the national airspace system, and future automation alternatives from a human factors perspective. The central premise of the analysis

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The Future of Air Traffic Control: Human Operators and Automation is that considerations of public safety require that the air traffic control system continue to be designed so that the human controller can intervene successfully as spot failures in the software or environmental disturbances require or can even assume manual control when the automation fails. The panel's first phase, which focused on the current system and its development, led to recommendations regarding safety and efficiency, system management, personnel selection and training, the development of an integrated approach to human factors, and system design considerations of human strengths and vulnerabilities. These recommendations and their supporting analyses are presented in Flight to the Future: Human Factors in Air Traffic Control, the panel's Phase I report. This second phase assesses future automation alternatives and the role of the human operator in ensuring safety and efficiency in the air traffic control system. Along with this assessment, the panel has included a human factors analysis of free flight focusing on its implications for the performance of air traffic controllers. The panel concludes that current system needs and the availability of various technologies 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 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 to 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. The complete set of the panel's conclusions and recommendations, presented in Chapter 10, covers (1) the general topics of locus of authority, levels of automation, recovery from failure and degradation, teamwork, and cross-cultural issues; (2) issues related to the design, development, and testing of specific systems; (3) free flight; and (4) the role of human factors in the process of introducing automation. In this summary, we present the most important recommendations, on levels of automation, system recovery from failure, locus of authority as it relates to automation and free flight, and the process of introducing automation. LEVELS OF AUTOMATION In the Phase I report, the panel identified a 10-level scale of automation relating to decision and action selection. At the extreme of total manual operation,

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The Future of Air Traffic Control: Human Operators and Automation a particular function is continuously performed by the human operator, with no machine control. At the other extreme of total automation, all aspects of the function (including its monitoring) are delegated to a machine, so that only the end-product and not its operation is made available to the human operator. In between these two extremes lie different degrees of participation in the function by the human and by automation. In this report we propose two additional scales, one representing levels of automation that can be applied to the dimension of information acquisition and integration (referred to as information automation) and another that is related to the dimension of action implementation. The level of information automation is determined by the presence or absence of computer functions enabling filtering, information distribution, information transformation, confidence estimates, integrity checks, and flexible information based on requests from users. Systems that possess all of these features have high levels of information automation. The dimension of action implementation is treated in this context as a dichotomous scale providing either manual or automatic implementation. The panel recommends that automation efforts focus on reliable, high level automation applications for information acquisition, integration, and presentation and for aiding controller decision making in order to support all system functions. Especially important in the near future is the development of decision aids for conflict resolution and maintaining separation. These aids should be directed primarily toward ensuring proper spacing between aircraft in preparation for the final stages of approach to landing and toward en route flight path efficiency improvement. The panel recommends implementation of high levels of automation of decision and action selection for system tasks involving relatively little uncertainty and risk. However, for system tasks associated with greater uncertainty and risk, automation of decision and action selection should not proceed beyond the level of suggesting a preferred decision/action alternative. Any consideration for automation at or above this level must be designed to prevent: loss of vigilance, loss of situation awareness, degradation of operational skills, and degradation of teamwork and communication. Such designs should also ensure the capabilities to overcome or counteract complacency, recover from failure, and provide a means of conflict resolution if loss of separation occurs. RECOVERY A central issue is the potential influence of automation on the ability to efficiently and effectively recover from emergency situations. Automation may increase capacity, but it will also increase traffic density and may increase airspace

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The Future of Air Traffic Control: Human Operators and Automation complexity by inducing changes in traffic flow from standard air routes. We predict that increases in traffic complexity and density will reduce the controller's situation awareness. We also anticipate that manual skills will degrade for most functions that one might automate, given the nearly universal findings that there is some forgetting and skill decay with disuse (although the magnitude of such a decline in air traffic control is not well-known). As a result, controllers are likely to react more slowly to emergencies if they require use of those manual skills during the recovery from a degraded state. Furthermore, it is anticipated that automation will introduce new procedures for recovery and that these procedures will also require training and practice. Developing training for emergency skills is a difficult problem because it requires preparation for an open-ended set of circumstances, many of which may never occur. Linking the two human performance elements of change in situation awareness and skill degradation makes it possible to predict the change in recovery response time—that is, the time required to respond appropriately to unexpected failure situations and intervene with manual control skills or alternative automated functionality. It is assumed that the less skilled controller, responding appropriately to a situation of which he has less awareness, will do so more slowly. Specifically, we predict that recovery response time will be greatly modulated by individual differences, characteristics of the team environment, the complexity of the airspace (number of response options), and the familiarity of procedures necessary to cope with a degraded system. All important safety consequences of system or component failures are related to the margin by which available time exceeds the recovery response time. In order to effectively predict recovery under a variety of conditions, it is necessary to develop models based on recovery scenarios that are based on human performance data concerning responses to low-probability events under different levels of skill degradation and lowered situation awareness. The panel recommends investing sufficient resources in studies of human response to low-probability emergencies; actively pursuing failure modes/fault tree analysis, particularly to identify situations in which two or more coordinating agents receive information inputs that are incongruous or contradictory; and involving human factors specialists in the development and testing of system recovery procedures. The panel recommends the development of models, for given designs and procedures, to examine the implications of recovery in a high-density, unstructured airspace created by increased capabilities of ground-based automation or free flight. The panel recommends the development of airspace safety models that can predict the likelihood of midair collisions, as a function of frequency

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The Future of Air Traffic Control: Human Operators and Automation and parameters of near-midair collisions1 and losses of separation,2for varying standards of traffic separation. To do this, models should be developed that are sensitive to loss of situation awareness and the possible degradation of skills that may result from moving controllers to progressively higher levels of automation of decision and action selection. The panel recommends that air traffic control subject-matter experts collaborate with specialists in the behavioral sciences to model individual and team responses to emergency situations and to populate the models with data to be collected in studies of human response time to low-probability emergencies. Policy makers should be made aware that choosing median response times to model these situations can have very different implications from those based on worst-case (longest) response times; these kinds of modeling choices must be carefully made and justified. The panel recommends that system functionality should be designed so that failure recovery will not depend on skills that are likely to degrade. LOCUS OF AUTHORITY Future airspace projections dictate a need for increases in capacity without sacrificing safety. Two alternative vehicles for accomplishing these goals have been proposed: a free flight scenario and a scenario involving ground-based authority; both presume automation. Any action or technology that moves to reduce pilot constraints on maneuvering is a move in the direction of free flight. There is, however, an important distinction between strategic free flight, in which route planning by the pilot in collaboration with the dispatcher is done in a manner that is unconstrained by air traffic control (i.e., free scheduling and free routing), and tactical free flight, in which the pilot is empowered to make flight path changes and conflict avoidance maneuvers without consulting the ground controller. There is of course a continuum of levels between strategic and tactical maneuvering. At least four different programs already involve some aspects of free flight: standard visual flight rules, the expanded national route program, the conflict resolution advisories of the traffic alert and collision avoidance system (TCAS), and the oceanic in-trail climb procedure. 1   Incidents associated with the operation of an aircraft in which a possibility of a collision occurs as a result of proximity of less than 500 feet to another aircraft, or a report is received from a pilot or flight crew member stating that a collision hazard existed between two or more aircraft. 2   Loss of separation is a condition in which the prevailing standards for separation are violated.

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The Future of Air Traffic Control: Human Operators and Automation A large number of issues must be addressed and resolved before determining if expanded concepts of free flight are feasible in an airspace whose regulators and users are committed to safety as a primary goal. It can be argued that any radical change to an already safe system will have at least the possibility of compromising safety. Unfortunately, given the complexity of the free flight concept, accurate assessment and prediction of its safety benefits may not be achievable for several years after its implementation. The versions of free flight that assume high levels of airborne authority have the predicted ability to greatly increase airspace flexibility and hence to potentially increase capacity as well. However, a large number of uncertainties are associated with safety. These include uncertainties as to how pilot-to-pilot negotiations will be resolved in worst-case scenarios; problems relating to controllers' maintaining awareness of the tactical situation in an airspace made more complex and dense by the implementation of free flight; the workload impact of both increasing decision load in the cockpit and increasing monitoring load on the ground; and issues regarding possible confusion in the residence of authority among air traffic controllers, pilots, and airline operations personnel. In considering these issues, the panel concludes that the residence of authority should be as unambiguous as possible to minimize opportunity for confusion between perceived and actual authority. For the foreseeable future, both actual and perceived authority should reside consistently and unambiguously on the ground. The justification is that authority on the ground is centralized, whereas authority in the air in a free flight regime is of necessity distributed among multiple aircraft, dispatchers, and controllers, and its residence would vary over time. Distributing authority flexibly across these agents is an invitation for ambiguity, which in turn compromises safety. The structural consistency of the airspace should be preserved. A major component of the controller's mental model of the airspace is associated with the enduring characteristics of a particular sector. Therefore, although air routes can and should be substantially modified from their current structure in order to improve efficiency, these modifications, once in place, should be relatively enduring in order to maintain safety. Air routes should not be altered on a flight-by-flight basis. Although more alternative routes may allow far greater flight path efficiency than in the current airspace, for example, by taking advantage of prevailing winds, there should be a fixed database of what these direct routes are, and an expectation that pilots will adhere to them (subject to controllers' granting of pilots' requests), in this way preserving consistency in the structure of the airspace. A ground-based scenario consistent with formulated plans of the Federal Aviation Administration can increase efficiency without radical changes in authority structure from the current system (e.g., the expanded national route program). The panel therefore recommends the development and

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The Future of Air Traffic Control: Human Operators and Automation fielding of current and proposed automation tools for ground-based air traffic control, following the guidelines specified in this report regarding the selection of levels of automation. We also recommend the vigorous pursuit of projections of how various tools will operate in concert. Because free flight design concepts that assume a high level of airborne authority over control of aircraft flight paths have more uncertainties than design options involving ground-based authority with increased automation, the panel recommends extreme caution before existing levels of free flight are further expanded to greater levels of pilot authority for separation. Furthermore, we recommend the conduct of extensive human-in-the-loop simulation studies and validation of human performance models before decisions are made regarding the further implementation of free flight; this is needed to obtain reliable prediction of the safety implications of worst-case scenarios. We also recommend heavy reliance on scenario walk-throughs and focus group sessions with controllers, pilots, traffic managers, and airline dispatchers. INTRODUCING AUTOMATION 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. These issues are discussed in detail in the panel's Phase I report. 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

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The Future of Air Traffic Control: Human Operators and Automation 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.