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Flight Deck Integration
HUMAN FACTORS IMPLICATIONS OF DATA LINK RESEARCH FOR ATCIFLIGHT DECK INTEGRATION K. Kerns The MITRE Coporation, McLean, VA 22102, U.S.A.
Abstract: Operationally-oriented research on data link was reviewed as a source of evidence on how human characteristics will interact with data link technology to affect the exchange of information between the ground system and the flight deck. The paper discusses the need for ATC/flight deck integration and then introduces key aspects of the integration problem. This is followed by a brief synthesis of the research findings on controller-pilot information transfer via data link. The research findings are analyzed with respect to operational and human factors issues in ATClflight deck integration. The conclusion of the paper discusses implications of the simulation research for ATClflight deck integration in the future system environment. Keywords: Aircraft Operations, Air Traffic Control, Communication Channels, Communications Systems, Human Factors, Information Integration
1. INTRODUCTION
transmitting instructions to carry out the plan. The role of the pilot receiving ATC services is one of processing advisory information, accepting instructions, and acting upon them (Billings and Cheaney, 1981).
Many believe that a new integrative mechanism, a digital data communications link, can help alleviate some of the problems in the current ATC environment and more effectively couple the groundside and airside resources to support operations in the future environment. This paper examines how a data link could be used in the current and future operational environment to reduce errors and enhance information transfer and to redistribute and balance controller and pilot workload. Operationally-oriented simulation research on data link is reviewed as the primary source of evidence on how human characteristics will interact with this new technology to affect the exchange of information between the ground system and the flight deck.
As the NAS has evolved to accommodate more traffic, this role relationship between controller and pilot is contributing to growing inefficiencies in ATC system performance. These inefficiencies may be largely attributable to divergent evolution of the complex airside and groundside human-technology systems in which the controllers and pilot are embedded. The technological capabilities and procedures used by controllers and pilots embedded in the ATC and air carrier organizations have been designed to interoperate within their respective organizational systems, not between them. As an example, controllers work with a two-dimensional, plan view display of traffic that is well suited to radar separation procedures and representation of vector solutions to separation and spacing problems. In contrast, procedures and flight management systems used by airline pilots support vertical profile planning in all flight phases to manage fuel and flight schedule requirements. Consequently,
1.1 Why A TC/Flight Deck Integration is Needed
Today' s ATC is based on a centralized, ground-based, human intensive system with the controller having a pivotal role in planning the movement of air traffic and
231
the pilot. Other factors that contribute to misinterpretation include (l) phonetic similarities in which the words used in the message lead to confusion in meaning or in the identity of the intended recipient, (2) transposition errors in which the sequence of numerals within the message was inaccurate, and (3) formulation errors in which messages were based on erroneous data or resulted from erroneous judgments. In addition, transcription errors in which messages are received correctly but are recorded erroneously or entered erroneously into airborne or ground systems have been noted in related studies of navigational errors.
vector instructions from controllers impose a high cognitive demand on pilots attempting to execute and maintain a prescribed vertical flight plan. Additionally, the operational communications procedures controllers and pilot use to coordinate their activities and conduct operations in different environments have not been developed to solve the overlying air-ground coordination problems. Rather, they have evolved incrementally, adapting to the capabilities and limitations of the voice radio communications system. The evolution of operational communications procedures piecemeal has resulted in a simultaneous over- and under-proceduralization of system operations and an allocation of responsibilities between controllers and pilots that is sometimes unbalanced (Degani and Weiner, 1994). Overproceduralization reduces system flexibility and opportunities for increased efficiency, while underproceduralization increases human stress and workload because operational demands and responses are not predictable (Adam et aI., 1994).
Especially in busy environments, the required timing of information transfers when controllers are preoccupied with higher priority tasks accounts for failures to transmit appropriate messages as well as untimely transmissions which are originated too late or too early to be useful to the recipient. For example, controllers are less likely to initiate traffic advisories during high traffic periods, precisely when the pilot's need for the information is greatest. Analyses of tape recordings of controller-pilot communications highlight the role of nonstandard communication procedures in information transfer problems (Morrow et aI., 1993; Cardosi, 1994). Although this research indicates that the actual incidence of communications errors is low, a much higher incidence of procedural deviations in which pilot do not follow standard procedures was observed. Moreover, the research also showed that errors and procedural deviations tended to increase as the complexity of the messages increased, requiring additional transmissions to correct or clarify a message.
1.2 Voice Communications
In the current A TC environment, the primary integrative mechanism supporting the exchange of information between controllers and pilots is voice messages carried by radiotelephone. Notwithstanding the care that has gone into designing the language and procedures for controller-pilot communications, the voice communication system does not always operate as intended. Studies of voice communications conclude that both human factors (distraction, forgetting, failure to monitor, nonstandard procedures, and phraseology) and system factors (unavailability of traffic information, frequency congestion, and high workload) contribute to information transfer deficiencies (Billings and Cheaney, 1981). This research also emphasizes that, in the busiest operating environments, the controller's and pilot's duty priorities are most apt to conflict, interfering with effective cross checking of mutual understanding and with timely transfer and acquisition of information.
1.3 Alternative Means of Information Transfer
Studies of voice communications also point out the urgent need for alternative means of transferring information that is now communicated exclusively by voice (Billings and Cheaney, 1981; Adarn et aI., 1994). Unlike voice radio, the data link communications medium can transmit coded, digital data to individual addresses. Data link system and transaction status is monitored through a built-in feedback path or protocol that automatically verifies the integrity of the message reaching the addressee and provides information to the sender concerning responses, interruptions, or failures . Once received, message data can be stored for future reference and formatted for easy access by the user. These features of data link can be expected to alleviate problems induced by user interaction with the voice radio system at nearly all stages of the communication process.
Research on information transfer problems in the aviation system generally concluded that the human tendency to fill-in information based on expectations when processing voice communications was implicated in many types of communication problems (Gray son and Billings, 1981). The expectation factor contributes to misinterpretations and inaccuracies because pilots and controllers sometimes hear what they expect to hear. This generates what have been called "readback and hearback" errors in which respectively a pilot perceives what he expected to hear in an instruction transmitted by a controller and a controller perceives what he expected to hear in the readback transmitted by
232
Reducing errors and enhancing information transfer are necessary conditions for effective integration of air and ground system resources, but they are not sufficient. In as much as inefficiencies in the current A TC system stem from the pattern of the workload and the timely availability of the information required to carry out tasks in the operating environment, efficient use of resources may also entail a redistribution and a reallocation of tasks among human and automated system elements to better exploit the resident capabilities. Controller and pilot acceptance of an altered allocation of functions is a critical consideration in ATClflight deck integration.
Off loading some of the voice radio message traffic onto another communication link will alleviate miscommunication problems caused by congestion. In addition, data link system capabilities such as discrete addressing of messages, preformatted messages and standard protocols, and preservation of information, can minimize radio-based problems like calI sign confusion, overlapping transmissions, procedural deviations, and memory lapses (Kerns, 1991 ; Morrow et al., 1993). Perhaps the greatest potential for improving information transfer via a data link wi\l come from exploiting device-independent message standards and coding which alIow flexible representation of information and direct interface of the data to automation systems. At the most basic level, standardization supports computeraiding to simplify the human's communication subtasks such as message formulation , communication system monitoring and error checking, and message logging. At a more sophisticated level, standardization supports transfers of data between aircraft and ground automation systems to ensure common databases and consistent solutions, without requiring the human to recode and reenter information.
Early experiments with cockpit display of traffic information (CDTI) concepts (Kreifeldt, 1980) showed that the preferred mode of air traffic management was a more distributed one in which both controllers and pilots participated. In these experiments, controllers were responsible for establishing an arrival sequence of aircraft and communicating the sequence order to the pilots; the pilots managed their position in the sequence and maintained spacing from other aircraft from that point on. This research showed that distributed management resulted in reduced controller workload and, although pilots reported a higher visual workload with CDTI, they stilI preferred distributed management. It was also significant that increased pilot workload was more than offset by the additional information provided by the CDTI and the associated perception of increased control of the situation. In contrast, controller acceptance of the alternative allocations of functions diminished with decreasing ground centralization of control.
Counterbalancing the potential improvements in information transfer are significant design challenges. Many of the basic principles and methods of effective voice communication also apply to data link but safety measures for data link must address different albeit analogous design and procedural issues. Visual display and manual control of transmitted information adds load to the human's busy visual information processing channel. Even though research suggests that a visual display may be less prone to misinterpretation than an acoustic display, visual perception is still susceptible to the effects of expectations and errors. The potential kinds of errors in visual perception also are predictable; confusion is no longer between information which sounds like other information when spoken but between alphanumeric characters and graphical codes which look alike or are physically adjacent (Billings and Cheaney, 1981; Morrow et al., 1993; Hopkin, 1994).
More recent work on the allocation of functions extends the scope of the integration problem to formally consider the next level of integration, including the role of the air carrier's aeronautical operational control center on the airside and the role of traffic flow management on the groundside. Central to this research is the notion of adapting the allocation of functions in specific flight phases and airspaces to take advantage of existing system capabilities and provide a more consistent level of service across areas that presently have markedly different procedures and technological capabilities (Sorenson et aI., 1992).
A visual communications medium is also more susceptible to failure at different points in the airground transfer process. Data link system capabilities can be exploited to standardize the content and procedures used in the ATC/flight deck segment of the information transfer path. However, new procedures will be needed to ensure coordination within controlIer teams and flight crews when the communications medium is silent and less readily observable by multiple operators.
2. SYNTHESIS OF DATA LINK SIMULATION STUDIES Although an aeronautical data link system is being developed to support a broad range of digital communications, including air-ground exchanges of weather, surveillance, and navigation information, the majority of the research conducted to date has focused on the use of data link for controller-pilot communications (FAA, 1994). This section synthesizes
1.4 Alternative Allocation of Functions
233
a number of conclusions concerning the operational impact and use of data link on the basis of a review of simulation studies. A more detailed review and discussion may be found in Kerns (1994).
workload limits by providing an additional channel for message generation and transmission, especially fort repetitive messages issued to each aircraft. Conversely, the pilot's visual and manual resources are already heavily loaded in some environments. In these situations, data link increases pereceived workload and could inappropriately interrupt and disrupt visual scanning and flight management tasks.
2.1 Reliability and Efficiency of Communications
The research consistently shows that using data link as an adjunct to voice communications improves the efficiency of pilot-controller communications by reducing the incidence of communications failures and, consequently, the number of attempts required for successful information transfer. In simulations, this effect is primarily attributable to the availability of a clearer, usable representation and a persistent, storable reference of message content; although in actual operations . errors caused by noise or blocked transmissions would also be avoided as would some message formulation and transcription/data transfer errors.
2.4 Operational Communications Procedures
Although the data link system inherently supports greater procedural consistency in the ATC/flight deck segment of the transfer, the silent communication process also requires extra measures, such as cockpit and controller team coordination procedures, display layouts, and voice generation technology, that will ensure access and understanding of information by multiple operators. 2.5 Information Access
2.2 Speed and Timing of Communications
The research further shows that redundant display formats widen the band of information available and improve the user's access to the particular features and data that are most compatible with the mental representation of the situation and task requirements. Operationally, both analytic and holistic processing of information are combined in many of the user's tasks. The simulation research highlights some specific classes of information, such as weather, traffic, and route, that are most likely to show benefits of more efficient and accurate assimilation when presented in spatially-oriented, graphical formats.
User perceptions and the performance of data link indicate that its superior reliability for controller-pilot communications is generally obtained at the cost of speed in the information transfer. Delay factors associated with message generation and transmission times account for longer total transaction times with data link than with voice. The time required for message interpretation and acknowledgment is comparable for the two media, although accuracy is improved with data link. Simulation results also reveal that, within limits, controllers and pilots can effectively adapt to the added delay by performing other tasks concurrently and adjusting the timing of their communications. Because of such adaptations, execution of ATC instructions seems to take about the same amount of time, regardless of the communications medium. However, the delay factors associated with message generation appear to limit data link's utility in rapidly changing conditions while transmission delays limit its utility for time-critical instructions.
2.6 Utilization of Human Information Processing Resources
Taken as a whole, the research indicates that data link allows controllers and pilots to devote more attention to critical communications functions such as interpreting, evaluating, and formulating messages. It does this by offering them relief from many of the overhead functions, such as repetitive message preparation, transcription of data to preserve information, and entry of data to provide input to other systems. The ability to automate these overhead functions while retaining human involvement in critical functions not only yields greater efficiency in operations by eliminating redundant transcription and data entry tasks; it also has great potential for preventing data entry errors and, when coupled with flexible display formatting, it should reduce the opportunity for errors of interpretation.
2.3 Workload
A redistribution in controller and pilot workload accompanies data link communications: visual and manual workloads increase while auditory and speech workloads decrease. This redistribution takes on operational significance in specific environments and for specific classes of information. In environments where severe frequency congestion currently exists, the controller's auditory and speech workload can reach an overload state. In such environments, data link helps to achieve more timely performance within acceptable
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2.7 Application of Data Link in the Current Environment 3.1 Human Role in Air Traffic Management Communications
According to the research, successful application of the data link to A TC/flight deck information exchanges depends on the operating environment in which the exchange occurs . Data link is generally more acceptable in less busy operational environments and flight phases, such as predeparture and en route (Kerns, 1991). However, the research further indicates that messages that can be prepared and issued in advance of final approach and landing operations should also be acceptable for data link in terminal airspace.
Data link research on air traffic management communications indicates that controllers and pilots should have final authority to approve the transfer of information to each other and to their automation systems. Consistent with this philosophy of management by approval is the notion of provisional approval wherein the human operator can delegate final approval of flight plan clearances and amendments to the automation system within the bounds of specific operating constraints and parameters. In addition, the application of management by approval should also include a range of approval options that enable the human operator to retain regular and meaningful involvement in the process. For example, human selection of specific messages for automatic transfer would be consistent with this philosophy, as would human selection of operating parameters that govern provisional approval of information transfers. Finally, use of automation to evaluate incoming messages and formulate preliminary approvals or identify potential constraint violations would constitute another variant consistent with this philosophy. Negotiation and collaborative decision making is an essential element in future ATM communications. Consistent with the previous research are several plausible ways of conducting the negotiation in a data link communications environment. The flexibility of voice communications could be exploited to work out a mutually agreed on decision, which in turn could be converted to a data link message by the pilot or controller, depending on the situation and the available system capabilities. Additionally, data link could be used to make information on situation constraints available for common access by controllers and pilots prior to negotiation or data link could be used in concert with automation for the iterative exchange of candidate flight path modifications. Controllers and pilots would manage the data link process using the various approval options described above.
Apart from considerations of the operating environment, study results also recommend use of data link to enhance or replace party line as a source of weather and traffic information. The failure of controllers to reliably and consistently transfer traffic avoidance information and the difficulty pilots experience in making use of critical party line information reveals that the current voice delivery mechanism is both unreliable and inefficient. The research further shows that in terms of the mental effort and attention required to access and recode information into usable representation of the situation, digital transfers of traffic, route, and weather information promise to improve both controller and pilot situation awareness.
3. IMPLICATIONS FOR THE EVOLUTION OF ATCIFLIGHT DECK INTEGRATION The strategic direction for the future system is called air traffic management (ATM). Recently, the FAA and the aviation industry reached consensus on a framework that will guide the redesign of the future A TM system. Central to this framework is a shift away from today ' s ground-based A TC operations toward a more cooperative arrangement in which users have greater freedom to select their flight paths and greater involvement in traffic and airspace management decisions. Closer cooperation will require the direct exchange of digital messages between airside and groundside automation systems to ensure common databases and consistent solutions to route planning and flight scheduling problems. A second design principle that underpins the ATM framework is the mandate to make full use of available airside and groundside resources in delivering air traffic services . Achievement of this goal implies the need to explore alternative allocations of functions, including adaptive assignment of separation assurance to the flight deck. Finally, the changes in controller-pilot role relationships and the flexibility in air-ground function allocation will require greater commonality in the information presented to controllers and pilots as they coordinate their activities.
3.2 Alternative Allocations of Functions Simulation results on data link applications confirm that while the addition of a digital communications link can address many information transfer problems, this capability alone will not be sufficient to address user acceptance issues. In partiCUlar, successful applications of data link in terminal area operations will depend on workload. Clear and unambiguous definition and operator notification of responsibilities will be needed to support shared awareness and expectations of controller and pilot action.
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Grayson, R.L., and e.E. Billings (1981). Information Transfer between Air Traffic Control and Aircraft: Communication Problems in Flight Operations. In e.E. Billings and E.S. Cheaney (Eds.), Information Transfer Problems in the Aviation System. NASA Technical Paper 1875. NASA Ames Research Center, Moffett Field, CA. Hopkin, D .V. (1994) . Human Performance Implications of Air Traffic Control Automation. In M. Mouloua and R. Parasuraman (Eds.) Human Performance in Automated Systems: Current Research and Trends (pp. 314-319). Lawrence Erlbaum, Hillsdale, NJ. Kerns, K. (1991). Data Link Communication between Controllers and Pilots: A Review and Synthesis of the Simulation Literature. The International Journal of Aviation Psychology, I (3), 181-204. Kerns, K. (1994). Human Factors in ATC/Flight Deck Integration: Implications of Data Link Simulation Research. MITRE Paper MP 94W98. The MITRE Corporation, McLean, VA. Kreifeldt, J.G. (1980). Cockpit Displayed Traffic Information and Distributed Management in Air Traffic Control. Human Factors, 22 (6), 671--691. Morrow, D., A. Lee, and M. Rodvold (1993). Analysis of Problems in Routine Controller-Pilot Communications. The International Journal of Aviation Psychology, 3 (4), 285-302.
3.3 Convergent Evolution of ATC and Flight Deck Functionality and Information
As user participation increases and air and ground system elements focus more on solving a common problem, the separate air and ground systems will begin to more closely resemble each other (Weiner, 1988). Data link research confirms that graphical presentations of traffic and weather information on the flight deck will improve the pilot's ability to obtain, assimilate, and interpret information and also provide a common point of reference that more closely resembles the controller's situation display. Although the definitions of comprehensive and coherent situation representations for controllers and pilots may never be identical, it is reasonable to assert that there will be greater commonality in terms of the types of information represented and the most efficient formats. ACKNOWLEDGMENTS This work was supported by the FAA Aeronautical Data Link Program. Portions of this material were presented previously at the 8th International Symposium on Aviation Psychology, April 1995, in Columbus, Ohio. This paper is adapted from Kerns (1994), which will also appear in D. Garland, J. Wise, and V. D. Hopkin (Eds.), Aviation Human Factors, Lawrence Erlbaum Associates Inc.
Sorenson et al. (1992). Opportunities for Integrating the Aircraft FMS with the Future Air Traffic Management System. 37th Annual Air Traffic Control Association conference Proceedings (pp. 534-543). ATCA Inc., Arlington, VA. Wiener, E.L. (1988). Cockpit Automation. In E.L. Weiner and D.C. Nagel (Eds.), Human Factors in Aviation (pp . 433-459) . Academic Press, Inc., San Diego, CA.
REFERENCES Adam, G.L., D.R. Kelley, and J.G. Steinbacher (1994). Reports by Airline Pilots on Airport Surface Operations: Part I . Identified Problems and Proposed Solutions for Surface Navigation and Communications. MTR 94W60, The MITRE Corporation, McLean, VA. Billings, e.E. and E.S. Cheaney (1981). Information Transfer Problems in the Avintion System. NASA Technical Paper 1875. NASA Ames Research Center, Moffett Field, CA. Cardosi, K. (1994). An Analysis of Tower (Local) Controller-Pilot Voice Communications. Report No. DOTIFANRD-94/l5 . V .S. Department of Transportation, Federal Aviation Administration, Washington, D.e. Degani, A., and E. Weiner (1994). On the Design of Flight Deck Procedures. NASA Contractor Report 177642. NASA Ames Research Center, Moffen Field, CA. Federal Aviation Administration (1994b). The Aeronautical Data Link System Operational Concept. V.S. Department of Transportation, Federal Aviation Administration, Washington D.e.
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Abstract: Operationally-oriented research on data link was reviewed as a source of evidence on how human characteristics will interact with data link technology to affect the exchange of information between the ground system and the flight deck. The paper discusses the need for ATC/flight deck integration and then introduces key aspects of the integration problem. This is followed by a brief synthesis of the research findings on controller-pilot information transfer via data link. The research findings are analyzed with respect to operational and human factors issues in ATClflight deck integration. The conclusion of the paper discusses implications of the simulation research for ATClflight deck integration in the future system environment. Keywords: Aircraft Operations, Air Traffic Control, Communication Channels, Communications Systems, Human Factors, Information Integration
1. INTRODUCTION
transmitting instructions to carry out the plan. The role of the pilot receiving ATC services is one of processing advisory information, accepting instructions, and acting upon them (Billings and Cheaney, 1981).
Many believe that a new integrative mechanism, a digital data communications link, can help alleviate some of the problems in the current ATC environment and more effectively couple the groundside and airside resources to support operations in the future environment. This paper examines how a data link could be used in the current and future operational environment to reduce errors and enhance information transfer and to redistribute and balance controller and pilot workload. Operationally-oriented simulation research on data link is reviewed as the primary source of evidence on how human characteristics will interact with this new technology to affect the exchange of information between the ground system and the flight deck.
As the NAS has evolved to accommodate more traffic, this role relationship between controller and pilot is contributing to growing inefficiencies in ATC system performance. These inefficiencies may be largely attributable to divergent evolution of the complex airside and groundside human-technology systems in which the controllers and pilot are embedded. The technological capabilities and procedures used by controllers and pilots embedded in the ATC and air carrier organizations have been designed to interoperate within their respective organizational systems, not between them. As an example, controllers work with a two-dimensional, plan view display of traffic that is well suited to radar separation procedures and representation of vector solutions to separation and spacing problems. In contrast, procedures and flight management systems used by airline pilots support vertical profile planning in all flight phases to manage fuel and flight schedule requirements. Consequently,
1.1 Why A TC/Flight Deck Integration is Needed
Today' s ATC is based on a centralized, ground-based, human intensive system with the controller having a pivotal role in planning the movement of air traffic and
231
the pilot. Other factors that contribute to misinterpretation include (l) phonetic similarities in which the words used in the message lead to confusion in meaning or in the identity of the intended recipient, (2) transposition errors in which the sequence of numerals within the message was inaccurate, and (3) formulation errors in which messages were based on erroneous data or resulted from erroneous judgments. In addition, transcription errors in which messages are received correctly but are recorded erroneously or entered erroneously into airborne or ground systems have been noted in related studies of navigational errors.
vector instructions from controllers impose a high cognitive demand on pilots attempting to execute and maintain a prescribed vertical flight plan. Additionally, the operational communications procedures controllers and pilot use to coordinate their activities and conduct operations in different environments have not been developed to solve the overlying air-ground coordination problems. Rather, they have evolved incrementally, adapting to the capabilities and limitations of the voice radio communications system. The evolution of operational communications procedures piecemeal has resulted in a simultaneous over- and under-proceduralization of system operations and an allocation of responsibilities between controllers and pilots that is sometimes unbalanced (Degani and Weiner, 1994). Overproceduralization reduces system flexibility and opportunities for increased efficiency, while underproceduralization increases human stress and workload because operational demands and responses are not predictable (Adam et aI., 1994).
Especially in busy environments, the required timing of information transfers when controllers are preoccupied with higher priority tasks accounts for failures to transmit appropriate messages as well as untimely transmissions which are originated too late or too early to be useful to the recipient. For example, controllers are less likely to initiate traffic advisories during high traffic periods, precisely when the pilot's need for the information is greatest. Analyses of tape recordings of controller-pilot communications highlight the role of nonstandard communication procedures in information transfer problems (Morrow et aI., 1993; Cardosi, 1994). Although this research indicates that the actual incidence of communications errors is low, a much higher incidence of procedural deviations in which pilot do not follow standard procedures was observed. Moreover, the research also showed that errors and procedural deviations tended to increase as the complexity of the messages increased, requiring additional transmissions to correct or clarify a message.
1.2 Voice Communications
In the current A TC environment, the primary integrative mechanism supporting the exchange of information between controllers and pilots is voice messages carried by radiotelephone. Notwithstanding the care that has gone into designing the language and procedures for controller-pilot communications, the voice communication system does not always operate as intended. Studies of voice communications conclude that both human factors (distraction, forgetting, failure to monitor, nonstandard procedures, and phraseology) and system factors (unavailability of traffic information, frequency congestion, and high workload) contribute to information transfer deficiencies (Billings and Cheaney, 1981). This research also emphasizes that, in the busiest operating environments, the controller's and pilot's duty priorities are most apt to conflict, interfering with effective cross checking of mutual understanding and with timely transfer and acquisition of information.
1.3 Alternative Means of Information Transfer
Studies of voice communications also point out the urgent need for alternative means of transferring information that is now communicated exclusively by voice (Billings and Cheaney, 1981; Adarn et aI., 1994). Unlike voice radio, the data link communications medium can transmit coded, digital data to individual addresses. Data link system and transaction status is monitored through a built-in feedback path or protocol that automatically verifies the integrity of the message reaching the addressee and provides information to the sender concerning responses, interruptions, or failures . Once received, message data can be stored for future reference and formatted for easy access by the user. These features of data link can be expected to alleviate problems induced by user interaction with the voice radio system at nearly all stages of the communication process.
Research on information transfer problems in the aviation system generally concluded that the human tendency to fill-in information based on expectations when processing voice communications was implicated in many types of communication problems (Gray son and Billings, 1981). The expectation factor contributes to misinterpretations and inaccuracies because pilots and controllers sometimes hear what they expect to hear. This generates what have been called "readback and hearback" errors in which respectively a pilot perceives what he expected to hear in an instruction transmitted by a controller and a controller perceives what he expected to hear in the readback transmitted by
232
Reducing errors and enhancing information transfer are necessary conditions for effective integration of air and ground system resources, but they are not sufficient. In as much as inefficiencies in the current A TC system stem from the pattern of the workload and the timely availability of the information required to carry out tasks in the operating environment, efficient use of resources may also entail a redistribution and a reallocation of tasks among human and automated system elements to better exploit the resident capabilities. Controller and pilot acceptance of an altered allocation of functions is a critical consideration in ATClflight deck integration.
Off loading some of the voice radio message traffic onto another communication link will alleviate miscommunication problems caused by congestion. In addition, data link system capabilities such as discrete addressing of messages, preformatted messages and standard protocols, and preservation of information, can minimize radio-based problems like calI sign confusion, overlapping transmissions, procedural deviations, and memory lapses (Kerns, 1991 ; Morrow et al., 1993). Perhaps the greatest potential for improving information transfer via a data link wi\l come from exploiting device-independent message standards and coding which alIow flexible representation of information and direct interface of the data to automation systems. At the most basic level, standardization supports computeraiding to simplify the human's communication subtasks such as message formulation , communication system monitoring and error checking, and message logging. At a more sophisticated level, standardization supports transfers of data between aircraft and ground automation systems to ensure common databases and consistent solutions, without requiring the human to recode and reenter information.
Early experiments with cockpit display of traffic information (CDTI) concepts (Kreifeldt, 1980) showed that the preferred mode of air traffic management was a more distributed one in which both controllers and pilots participated. In these experiments, controllers were responsible for establishing an arrival sequence of aircraft and communicating the sequence order to the pilots; the pilots managed their position in the sequence and maintained spacing from other aircraft from that point on. This research showed that distributed management resulted in reduced controller workload and, although pilots reported a higher visual workload with CDTI, they stilI preferred distributed management. It was also significant that increased pilot workload was more than offset by the additional information provided by the CDTI and the associated perception of increased control of the situation. In contrast, controller acceptance of the alternative allocations of functions diminished with decreasing ground centralization of control.
Counterbalancing the potential improvements in information transfer are significant design challenges. Many of the basic principles and methods of effective voice communication also apply to data link but safety measures for data link must address different albeit analogous design and procedural issues. Visual display and manual control of transmitted information adds load to the human's busy visual information processing channel. Even though research suggests that a visual display may be less prone to misinterpretation than an acoustic display, visual perception is still susceptible to the effects of expectations and errors. The potential kinds of errors in visual perception also are predictable; confusion is no longer between information which sounds like other information when spoken but between alphanumeric characters and graphical codes which look alike or are physically adjacent (Billings and Cheaney, 1981; Morrow et al., 1993; Hopkin, 1994).
More recent work on the allocation of functions extends the scope of the integration problem to formally consider the next level of integration, including the role of the air carrier's aeronautical operational control center on the airside and the role of traffic flow management on the groundside. Central to this research is the notion of adapting the allocation of functions in specific flight phases and airspaces to take advantage of existing system capabilities and provide a more consistent level of service across areas that presently have markedly different procedures and technological capabilities (Sorenson et aI., 1992).
A visual communications medium is also more susceptible to failure at different points in the airground transfer process. Data link system capabilities can be exploited to standardize the content and procedures used in the ATC/flight deck segment of the information transfer path. However, new procedures will be needed to ensure coordination within controlIer teams and flight crews when the communications medium is silent and less readily observable by multiple operators.
2. SYNTHESIS OF DATA LINK SIMULATION STUDIES Although an aeronautical data link system is being developed to support a broad range of digital communications, including air-ground exchanges of weather, surveillance, and navigation information, the majority of the research conducted to date has focused on the use of data link for controller-pilot communications (FAA, 1994). This section synthesizes
1.4 Alternative Allocation of Functions
233
a number of conclusions concerning the operational impact and use of data link on the basis of a review of simulation studies. A more detailed review and discussion may be found in Kerns (1994).
workload limits by providing an additional channel for message generation and transmission, especially fort repetitive messages issued to each aircraft. Conversely, the pilot's visual and manual resources are already heavily loaded in some environments. In these situations, data link increases pereceived workload and could inappropriately interrupt and disrupt visual scanning and flight management tasks.
2.1 Reliability and Efficiency of Communications
The research consistently shows that using data link as an adjunct to voice communications improves the efficiency of pilot-controller communications by reducing the incidence of communications failures and, consequently, the number of attempts required for successful information transfer. In simulations, this effect is primarily attributable to the availability of a clearer, usable representation and a persistent, storable reference of message content; although in actual operations . errors caused by noise or blocked transmissions would also be avoided as would some message formulation and transcription/data transfer errors.
2.4 Operational Communications Procedures
Although the data link system inherently supports greater procedural consistency in the ATC/flight deck segment of the transfer, the silent communication process also requires extra measures, such as cockpit and controller team coordination procedures, display layouts, and voice generation technology, that will ensure access and understanding of information by multiple operators. 2.5 Information Access
2.2 Speed and Timing of Communications
The research further shows that redundant display formats widen the band of information available and improve the user's access to the particular features and data that are most compatible with the mental representation of the situation and task requirements. Operationally, both analytic and holistic processing of information are combined in many of the user's tasks. The simulation research highlights some specific classes of information, such as weather, traffic, and route, that are most likely to show benefits of more efficient and accurate assimilation when presented in spatially-oriented, graphical formats.
User perceptions and the performance of data link indicate that its superior reliability for controller-pilot communications is generally obtained at the cost of speed in the information transfer. Delay factors associated with message generation and transmission times account for longer total transaction times with data link than with voice. The time required for message interpretation and acknowledgment is comparable for the two media, although accuracy is improved with data link. Simulation results also reveal that, within limits, controllers and pilots can effectively adapt to the added delay by performing other tasks concurrently and adjusting the timing of their communications. Because of such adaptations, execution of ATC instructions seems to take about the same amount of time, regardless of the communications medium. However, the delay factors associated with message generation appear to limit data link's utility in rapidly changing conditions while transmission delays limit its utility for time-critical instructions.
2.6 Utilization of Human Information Processing Resources
Taken as a whole, the research indicates that data link allows controllers and pilots to devote more attention to critical communications functions such as interpreting, evaluating, and formulating messages. It does this by offering them relief from many of the overhead functions, such as repetitive message preparation, transcription of data to preserve information, and entry of data to provide input to other systems. The ability to automate these overhead functions while retaining human involvement in critical functions not only yields greater efficiency in operations by eliminating redundant transcription and data entry tasks; it also has great potential for preventing data entry errors and, when coupled with flexible display formatting, it should reduce the opportunity for errors of interpretation.
2.3 Workload
A redistribution in controller and pilot workload accompanies data link communications: visual and manual workloads increase while auditory and speech workloads decrease. This redistribution takes on operational significance in specific environments and for specific classes of information. In environments where severe frequency congestion currently exists, the controller's auditory and speech workload can reach an overload state. In such environments, data link helps to achieve more timely performance within acceptable
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2.7 Application of Data Link in the Current Environment 3.1 Human Role in Air Traffic Management Communications
According to the research, successful application of the data link to A TC/flight deck information exchanges depends on the operating environment in which the exchange occurs . Data link is generally more acceptable in less busy operational environments and flight phases, such as predeparture and en route (Kerns, 1991). However, the research further indicates that messages that can be prepared and issued in advance of final approach and landing operations should also be acceptable for data link in terminal airspace.
Data link research on air traffic management communications indicates that controllers and pilots should have final authority to approve the transfer of information to each other and to their automation systems. Consistent with this philosophy of management by approval is the notion of provisional approval wherein the human operator can delegate final approval of flight plan clearances and amendments to the automation system within the bounds of specific operating constraints and parameters. In addition, the application of management by approval should also include a range of approval options that enable the human operator to retain regular and meaningful involvement in the process. For example, human selection of specific messages for automatic transfer would be consistent with this philosophy, as would human selection of operating parameters that govern provisional approval of information transfers. Finally, use of automation to evaluate incoming messages and formulate preliminary approvals or identify potential constraint violations would constitute another variant consistent with this philosophy. Negotiation and collaborative decision making is an essential element in future ATM communications. Consistent with the previous research are several plausible ways of conducting the negotiation in a data link communications environment. The flexibility of voice communications could be exploited to work out a mutually agreed on decision, which in turn could be converted to a data link message by the pilot or controller, depending on the situation and the available system capabilities. Additionally, data link could be used to make information on situation constraints available for common access by controllers and pilots prior to negotiation or data link could be used in concert with automation for the iterative exchange of candidate flight path modifications. Controllers and pilots would manage the data link process using the various approval options described above.
Apart from considerations of the operating environment, study results also recommend use of data link to enhance or replace party line as a source of weather and traffic information. The failure of controllers to reliably and consistently transfer traffic avoidance information and the difficulty pilots experience in making use of critical party line information reveals that the current voice delivery mechanism is both unreliable and inefficient. The research further shows that in terms of the mental effort and attention required to access and recode information into usable representation of the situation, digital transfers of traffic, route, and weather information promise to improve both controller and pilot situation awareness.
3. IMPLICATIONS FOR THE EVOLUTION OF ATCIFLIGHT DECK INTEGRATION The strategic direction for the future system is called air traffic management (ATM). Recently, the FAA and the aviation industry reached consensus on a framework that will guide the redesign of the future A TM system. Central to this framework is a shift away from today ' s ground-based A TC operations toward a more cooperative arrangement in which users have greater freedom to select their flight paths and greater involvement in traffic and airspace management decisions. Closer cooperation will require the direct exchange of digital messages between airside and groundside automation systems to ensure common databases and consistent solutions to route planning and flight scheduling problems. A second design principle that underpins the ATM framework is the mandate to make full use of available airside and groundside resources in delivering air traffic services . Achievement of this goal implies the need to explore alternative allocations of functions, including adaptive assignment of separation assurance to the flight deck. Finally, the changes in controller-pilot role relationships and the flexibility in air-ground function allocation will require greater commonality in the information presented to controllers and pilots as they coordinate their activities.
3.2 Alternative Allocations of Functions Simulation results on data link applications confirm that while the addition of a digital communications link can address many information transfer problems, this capability alone will not be sufficient to address user acceptance issues. In partiCUlar, successful applications of data link in terminal area operations will depend on workload. Clear and unambiguous definition and operator notification of responsibilities will be needed to support shared awareness and expectations of controller and pilot action.
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Grayson, R.L., and e.E. Billings (1981). Information Transfer between Air Traffic Control and Aircraft: Communication Problems in Flight Operations. In e.E. Billings and E.S. Cheaney (Eds.), Information Transfer Problems in the Aviation System. NASA Technical Paper 1875. NASA Ames Research Center, Moffett Field, CA. Hopkin, D .V. (1994) . Human Performance Implications of Air Traffic Control Automation. In M. Mouloua and R. Parasuraman (Eds.) Human Performance in Automated Systems: Current Research and Trends (pp. 314-319). Lawrence Erlbaum, Hillsdale, NJ. Kerns, K. (1991). Data Link Communication between Controllers and Pilots: A Review and Synthesis of the Simulation Literature. The International Journal of Aviation Psychology, I (3), 181-204. Kerns, K. (1994). Human Factors in ATC/Flight Deck Integration: Implications of Data Link Simulation Research. MITRE Paper MP 94W98. The MITRE Corporation, McLean, VA. Kreifeldt, J.G. (1980). Cockpit Displayed Traffic Information and Distributed Management in Air Traffic Control. Human Factors, 22 (6), 671--691. Morrow, D., A. Lee, and M. Rodvold (1993). Analysis of Problems in Routine Controller-Pilot Communications. The International Journal of Aviation Psychology, 3 (4), 285-302.
3.3 Convergent Evolution of ATC and Flight Deck Functionality and Information
As user participation increases and air and ground system elements focus more on solving a common problem, the separate air and ground systems will begin to more closely resemble each other (Weiner, 1988). Data link research confirms that graphical presentations of traffic and weather information on the flight deck will improve the pilot's ability to obtain, assimilate, and interpret information and also provide a common point of reference that more closely resembles the controller's situation display. Although the definitions of comprehensive and coherent situation representations for controllers and pilots may never be identical, it is reasonable to assert that there will be greater commonality in terms of the types of information represented and the most efficient formats. ACKNOWLEDGMENTS This work was supported by the FAA Aeronautical Data Link Program. Portions of this material were presented previously at the 8th International Symposium on Aviation Psychology, April 1995, in Columbus, Ohio. This paper is adapted from Kerns (1994), which will also appear in D. Garland, J. Wise, and V. D. Hopkin (Eds.), Aviation Human Factors, Lawrence Erlbaum Associates Inc.
Sorenson et al. (1992). Opportunities for Integrating the Aircraft FMS with the Future Air Traffic Management System. 37th Annual Air Traffic Control Association conference Proceedings (pp. 534-543). ATCA Inc., Arlington, VA. Wiener, E.L. (1988). Cockpit Automation. In E.L. Weiner and D.C. Nagel (Eds.), Human Factors in Aviation (pp . 433-459) . Academic Press, Inc., San Diego, CA.
REFERENCES Adam, G.L., D.R. Kelley, and J.G. Steinbacher (1994). Reports by Airline Pilots on Airport Surface Operations: Part I . Identified Problems and Proposed Solutions for Surface Navigation and Communications. MTR 94W60, The MITRE Corporation, McLean, VA. Billings, e.E. and E.S. Cheaney (1981). Information Transfer Problems in the Avintion System. NASA Technical Paper 1875. NASA Ames Research Center, Moffett Field, CA. Cardosi, K. (1994). An Analysis of Tower (Local) Controller-Pilot Voice Communications. Report No. DOTIFANRD-94/l5 . V .S. Department of Transportation, Federal Aviation Administration, Washington, D.e. Degani, A., and E. Weiner (1994). On the Design of Flight Deck Procedures. NASA Contractor Report 177642. NASA Ames Research Center, Moffen Field, CA. Federal Aviation Administration (1994b). The Aeronautical Data Link System Operational Concept. V.S. Department of Transportation, Federal Aviation Administration, Washington D.e.
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