User Request Evaluation Tool and Controller-Pilot ...

User Request Evaluation Tool (URET) and Controller-Pilot Data Link Communications (CPDLC) Integration Benefits Assessment Jasenka Rakas University of California at Berkeley National Center of Excellence for Aviation Operations Research Institute for Transportation Studies 107D McLaughlin Hall Berkeley, CA 94720 Tel: (510) 642-9064 Fax: (510) 642-1246 E-mail: [email protected] Mark Hansen University of California at Berkeley National Center of Excellence for Aviation Operations Research Department of Civil and Environmental Engineering 107B McLaughlin Hall Berkeley, CA 94720 Tel: (510) 642-2880 Fax: (510) 642-1246 E-mail: [email protected] Wanjira Jirajaruporn National Center of Excellence for Aviation Operations Research Department of Civil and Environmental Engineering 107E McLaughlin Hall Berkeley, CA 94720 Tel: (510) 642-4609 Fax: (510) 642-1246 E-mail: [email protected] Tanja Bolic University of California at Berkeley National Center of Excellence for Aviation Operations Research Department of Civil and Environmental Engineering 107E McLaughlin Hall Berkeley, CA 94720 Tel: (510) 642-4609 Fax: (510) 642-1246 E-mail: [email protected] November 2002

Submitted for presentation at the 2003 Annual Meeting of the Transportation Research Board and for publication in the Transportation Research Record 7,214 word equivalent

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User Request Evaluation Tool (URET) and Controller-Pilot Data Link Communications (CPDLC) Integration Benefits Assessment Abstract This paper explores benefits of integrating User Request Evaluation Tool (URET) and Controller-Pilot Data Link Communications (CPDLC). Controller-pilot voice-communication messages and aircraft traffic flows/conflicts are analyzed in great detail in one representative, URET-operating en route sector. Based on the mapped URET data and the real-world communication messages, a base-case and two alternative scenarios were analyzed to (1) estimate the number of clearances that are given to pilots to resolve aircraft conflicts a sufficient time before the start of the conflict, and (2) determine if any reduction in frequency congestion could be achieved if such messages were sent via data link. It was found that the highest frequency utilization, which corresponded to the first traffic peak, was reduced 27.46% after the second-scenario messages were removed from the base-case scenario. After removing the non-time critical conflict resolution messages, the total reduction was 58.57%. Frequency utilization during the highest number of aircraft conflicts was reduced 64.55% after all messages from the second and the third scenario were removed. Thus, the benefits of integrating CPDLC and URET are significant. If non-time critical conflict messages were transmitted via data link in the integrated CPDLC/URET environment, they could bring considerable improvements to the frequency congestion. More importantly, the largest benefits would be felt in situations that involve a large number of aircraft conflicts, or during busy periods of traffic. These improvements could further help reduce the number of communication errors (and the consequent ATC workload), as well as the number of operational errors. KEYWORDS: air traffic control, communication messages, CPDLC, integration benefits, URET

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User Request Evaluation Tool (URET) and Controller-Pilot Data Link Communications (CPDLC) Integration Benefits Assessment INTRODUCTION As National Airspace System (NAS) modernization progresses, and the Free Flight Phase 1 (FFP1) moves to Phase 2, it is vital to the operational efficiency of the NAS and traffic safety to continuously evaluate the benefits of new decision support tools and communication-navigationsurveillance (CNS) technologies used in air traffic control. An important and often overlooked aspect of the evaluation concerns the integration of tools and technologies. Integration can often lead to additional benefits not captured when the component systems are used individually. The Federal Aviation Administration (FAA), through its Office of Air Traffic Systems Development (and the En Route Integrated product Team, AUA-200) supports the Aeronautical Data Link System (ADLS) Build II program. This program is concerned with benefits estimation for integration of en route decision support tools (DST) with data link, and the operation of the same tools in a non-integrated environment. The benefits and performance of new decision support tools to assist en route air traffic controllers (such as the User Request Evaluation tool -- URET), have continuously been evaluated since 1997. During the summer of 2002, a new automation tool, called ControllerPilot Data Link Communications (CPDLC), has been introduced for the first time in the NAS. The tool is used for transmitting voice communication messages between controllers and pilots via data link. It is anticipated that after the initial deployment, CPDLC will first be co-located, and then integrated with URET. The User Request Evaluation Tool is the en route controller tool used to automatically detect and help resolve aircraft-to-aircraft and aircraft-to-airspace conflicts, trial planning of proposed Flight Plan amendments, automated controller coordination of problem resolutions, and enhanced flight data management. To date, this tool has been deployed in Indianapolis (ZID), Memphis (ZME), Kansas City (ZKC), Chicago (ZAU), Cleveland (ZOB), Washington (ZDC), and Atlanta (ZTL) Air Route Traffic Control Centers (ARTCC). The Controller Pilot Data Link Communications is the Aeronautical Data Link System (ADLS) that provides a data communication between aircraft and ground automation system in en route sector. The Controller Pilot Data Link System complements voice communications and provides a link that is only used (in the initial Build phase) for routine messages, which make up about a half of all controller/pilot communications messages. To date, the only ARTCC site that has deployed CPDLC is Miami Center (ZMA). Since June 2002, this first phase, called CPDLC Build I, has provided four operational services in ZMA: (1) transfer of communication, (2) initial contact, (3) altimeter setting, and (4) informational menu text. Under the Build IA phase, which is planned to be deployed in early 2004, the additional messages transmitted via data link will include assignment of speeds, headings, pilot-initiated altitude requests, and route clearances. Thus, the exchange of controller/pilot communications will start to occur in an integrated aural/visual environment, where the number of messages transmitted by CPDLC will gradually evolve and become more dominant. Both URET and CPDLC will continue to be incrementally deployed throughout the National Airspace System. The coordinated deployments consist of two phases: the co-location phase and the integration phase. Under the co-location phase, URET and CPDLC will be

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installed on the Display System Replacement (DSR) hardware platform. Both URET and CPDLC have a two-way interface to the Host computer but not a direct interface for data transfer between the tools. Later, in the integration phase, there will be direct data transfer of data between these tools. The research reported here, sponsored by the Aeronautical Data Link System (ADLS) Build II program, investigates one of the potential benefits of integrating URET and CPDLC -the ability to deliver URET-generated conflict resolution messages via data link.

Background The development of CPDLC is partially a response to the channel frequency congestion problem, which quite often occurs in busy sectors when many aircraft (i.e., pilots) attempt to communicate with an air traffic controller (by adjusting their VHF radio to a designated frequency). Because each communication message takes a certain amount of time, it happens that during busy traffic periods there is a point of saturation on a communication channel where an air traffic controller cannot receive/transmit any additional messages. Consequently, during that period, no additional aircraft can be managed within the controller’s assigned airspace. Errors, miscommunications and message repeats also contribute to the frequency congestion and unnecessary increase in the controller/pilot workload. In the new CPDLC environment, many messages will be transmitted via data link, which will consequently reduce a frequency congestion/utilization. Controllers and pilots will use CPDLC displays and keys (Kerns, 2001) to compose, send and receive messages. Controllers and pilots will be able to compose messages depending on the message type. For example, altitude or route clearances will have a letter S affixed to the computer input when a controller composes a message to update the aircraft’s flight plan entry. This letter S will indicate that the computer must compose an altitude or route clearance message before sending it to the aircraft. When such a message arrives via data link to the cockpit, it is shown to the flight crew on the display. Then, a pilot acknowledges that he received a message by pressing a specific key.

Problem Statement and Objectives The two major questions this research is concerned about are: 1. Is it feasible to communicate conflict resolution messages using CPDLC in the integrated environment? The key issue here is to determine if these clearances will be received in time to avoid loss of safety margins. 2. If it is feasible, what would be the impact on the frequency utilization? In this part, a comparison scenario is created in which these conflict resolution messages have been eliminated from the voice traffic to a scenario in which only other types of messages have been eliminated. The answers to these questions are based on the analysis of one particular sector, during 4 hours and 15 minutes of traffic, and not on the whole National Airspace System (NAS). However, methodology developed in this research can be repeated for studies of other sectors (and consequently for the NAS). Along the way to answering those questions, a long array of issues

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was analyzed, including controller-pilot voice-communication messages, traffic characteristics, URET alerts, and aircraft conflicts.

DESCRIPTION OF THE STUDY AREA A representative, medium-size, super-high altitude en route Sector 91 has been selected as a study area. This sector is a part of the Indianapolis Air Route Traffic Control Center (ZID), and has used URET as a support tool for a Data (D)-controller since 1997. The sector is surrounded by the Kansas City Center to the West, Sector 90 to the North, Sector 92 to the East, and the Memphis Center to the South (Figure 1). The data from the Host Computer were loaded into URET for a representative day of traffic (August 31, 2000), between 18:45 pm – 23:00 pm ZULU time (i.e., Greenwich Mean Time). The analysis of URET data showed that the number of aircraft controlled by the Sector at one instant was as low as 1 aircraft (20:25 pm), and as high as 14 aircraft (20:40 pm), with the peak between 20:40 pm and 21:10 pm (Figure 7).

METHODOLOGY Methodology developed in this research is documented in figure 2, which relates voicecommunication activities to traffic situation, and to URET conflict alerts. Models used to support various analyses that are part of developed methodology are documented in table 1. In the first phase, we identified voice-communication messages whose purpose was conflict resolution. Then, it was determined how much time was available to communicate those messages, which was compared with the expected performance of CPDLC. In the next step, the identified messages were analyzed (1) to determine which messages would be transmitted via CPDLC, and (2) to quantify their impact on frequency utilization. Although the objective was straightforward, the research involved very complex relations among tools used and parameters derived. Because such research on examining benefits of integrated URET/CPDLC environment was not conducted before, and published literature was not found to date, the study faced many challenges and issues. The end result was a set of messages used to resolve aircraft conflicts, and for each message, a set of four times and three time intervals associated with it (Figure 3). The times were derived either from the URET log file, or from the real-world transcribed message file. Time t1, (URET’s notification to the controller as to an impeding conflict) was derived from the URET log file, which contained URET data for all aircraft alerts in Sector 91 (Table 2). Time t2 (aircraft checking-in time into the sector -- indicating the first time an aircraft established communication with a controller in a new sector ), and t3 (clearance issued by controller -indicating the time a controller issued a clearance to the pilot to resolve a conflict) were obtained from the transcribed controller-pilot communication messages. The parameter t4 (URET start of conflict occurred) was obtained from URET log file for Sector 91 (Table 2), which indicated the time URET predicted the start of a conflict. Based on these times, three time intervals were defined accordingly (Figure 3): a) A = t3 - t1 = time between controller’s clearance and URET’s first conflict notification b) B = t4 - t3 = time between URET-predicted conflict start time and controller’s clearance,

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c) C = t3 - t2 = time between controller’s clearance and the first time aircraft checks in. Calculation of these time-intervals was instrumental in determining if conflict-resolution messages could be transmitted via data link. Interval B was the most relevant because it directly indicated the amount of time left to a URET-predicted conflict after an air traffic controller issued a clearance. The interval depicted a relationship between (i) the time a real-action was taken and (ii) the automation tool (i.e., URET) conflict time. Interval A was a very useful MOP because it showed the amount of time it took an air traffic controller to issue a conflict-resolution clearance after the initial conflict notification by URET. Both measures helped better understand air traffic controller’s promptness and efficiency in resolving conflict situations. Interval C was derived to provide background information on the amount of time passed to obtain a conflictresolution clearance after a pilot established communication with an air traffic controller for the first time. In addition, a sum of A and B indicated the total URET prediction time, and was useful in observing changes in URET conflict-prediction time with respect to traffic density.

Issues and Problems Encountered The first issue was to determine if the message was used for a standard clearance or to resolve a conflict. To determine that, it was critical to understand how URET generates alerts, and under what scenarios a controller issues a clearance. In URET, a single alert represents a conflict between only two aircraft. If Aircraft X simultaneously has a conflict with Aircraft Y and also with Aircraft Z, but Aircraft Y and Aircraft Z are not in conflict, two URET alerts will be generated. The criteria URET uses to declare an alert are rather complicated (Brudnicki et al, 1996; Brudnicki and McFarland, 1997; Kerns and McFarland, 1998; Winokur, 2000) and depend on several parameters. In the data derived from URET, one pair of aircraft can only contribute to at most one alert count. If an alert is ever notified for that pair of aircraft, one alert is counted regardless of its “degree”. The alert is counted as being notified to the sector that was first notified of a URET alert for that pair. If the alert is subsequently notified to a different sector, that second sector will not receive an alert count for that pair. To do a systematic analysis of conflicts and clearances, we compiled the list of all clearances to aircraft, and then those of concern were analyzed in great detail using URET and XEVAL (Figure 4). After an initial “look” at a list of clearances to aircraft, it was found that the controller issues clearances to aircraft for a variety of reasons, and the most common are to: 1. Solve an aircraft-to-aircraft potential conflict, thereby maintaining required separations. 2. Meet a required altitude restriction. 3. Give a series of routine altitude clearances to get the aircraft between cruise altitude and the airport. A single clearance in this series is often given in this situation until a controller can affect a handoff, or coordinate with the next sector for a higher or lower altitude. 4. Meet an active Miles-in-Trail restriction that applies to the subject flight. 5. Maneuver an aircraft to avoid restricted airspace. 6. Reroute an aircraft to comply with Traffic Management directives or established ATCpreferred routes.

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7. Expedite an aircraft by sending it direct to a downstream fix. 8. Maneuver an aircraft around severe weather. 9. Respond to a pilot request. The second concern was to determine what type of conflict was the message resolving. Messages were issued to resolve either horizontal (“turn left 20 degrees for traffic”), or vertical (“maintain 2,500 ft or greater through FL 350”) conflicts. In some cases the situation was ambiguous, and the controller had to meet several objectives in a single clearance. And sometimes, the single clearance solved conflicts between the subject aircraft and several object aircraft. There were also cases in which URET conflicts were notified to a sector for which the controller gave no conflict resolution messages. The controller may have judged that the conflict required no resolution. The conflict may also have been resolved by a clearance given by the controller who handled the flight prior to the notification sector. The problem may have been solved by a clearance from a controller for a flight the subject sector never handled. Other URET alerts may be resolved by delaying a maneuver that URET predicted would occur. An example is an aircraft at cruise altitude approaching the top of descent point. Another challenging issue was to determine the start of a URET-generated conflict time t4. Whenever URET determines that the current aircraft trajectory is not adequately reflecting the motion of the aircraft as represented by the track reports, it builds a new trajectory that begins at the latest track report. So it is possible that, for the duration of a single conflict notified to a sector, there may be more than one predicted start of conflict time. In this research, t4 was determined by using the data from the log file for URET trajectories of the two aircraft that were active at the time the controller gave a voice clearance to resolve the conflict (Table 2). Finally, we needed to identify voice transmissions with a “large” amount of lead time (B value) that could be considered non-time critical. Out of 1,206 communication messages analyzed, there were 200 clearances that “looked” like conflicts (for example, they involved horizontal or vertical clearances, type of additional wording controllers used in communications with pilots, etc). Out of 200 clearances, 57 were defined as conflicts, based on XEVAL and URET, and the methodology summarized in figure 2. Out of 57 conflicts, 49 messages were related to solving horizontal conflicts, and 8 messages were issued for vertical conflicts. A selection of messages with “large” B values was based on interviews with air traffic controllers and available literature (Human Factors Task Force, 1992; Rehmann 1997; Smolensky and Stein, 1998). The findings suggested that it was not possible to define a unique B value as a standard buffer between URET-predicted conflict start time (t4) and controller’s clearance (t3) to decide if a message is suitable for data link. Because the B value depended on a number of factors, each situation/conflict was analyzed in a broader context: as a function of traffic density, number of aircraft in the sector, type of clearances (horizontal or vertical conflict resolution, if a controller used a key word “for traffic” in communicating with a pilot), number of aircraft in conflict, etc. Thus, the B value had a minimum conservative range between 5-8 minutes, depending on the situation.

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Recording and Transcribing Controller-pilot Communication Messages The tape recordings of controller-pilot radio communication messages were transcribed for Sector 91 using a machine called “Reproducer”, a high-capacity 60-channel voice recorder to extract 4 hours and 15 minutes of voice communication onto cassette tapes. The voice recordings were precisely synchronized with the radar data, allowing a correct mapping of messages and the aircraft traffic. Each tape has 60 channels, and communication messages on all channels were recorded on the same device. The Reproducer (the playback machine) had capabilities to manipulate messages, select specific channels and rewind a 24-hour tape in 2-3 minutes. It was possible to transport (i.e., copy) voice communication messages from one tape onto 90 minute cassette tapes (Table 1 and Figure 2).

ANALYSES RESULTS Time Differences among Controller’s Clearance, URET Alert Notification, Aircraft Checking-in and URET-predicted Conflict Start The 57 situations that were verified as conflicts were further analyzed and the findings were depicted in figure 5. The time difference A (between controller’s clearance (t3) and URET alert notification (t1), per 15-minute intervals) closely followed the number of aircraft in sector (correlation 0.8). Parameter A had the highest value during the peak traffic period of 20:30-21:15 (Zulu time). This indicated that, as expected, it took an air traffic controller the longest time to issue a clearance (after URET’s alert notification) when traffic was very busy. Similarly, the time difference C (between aircraft check-in (t2) and the controller’s clearance (t3)) was still higher during the peak period than the average value. On the other hand, the B value (time difference between URET-predicted conflict start (t4) and controller’s clearance time (t3)), whose mean and standard deviation over the whole sample were 4.1 and 3.1 minutes respectively, has a higher average value—6.5 minutes--during the peak period. This means that as the traffic got busier, the controllers were able to increase the buffer B. The numerical explanation for this is that during the peak period the times from URET alert and from sector check-in to conflict (t4 - t1 and t4 – t2 respectively) both increased. The underlying cause for this pattern and whether it generalizes to other situations are questions for further research, but for the case we investigated, it means that conflict resolution messages could be off-loaded to CPDLC most readily during the busy times when it would be most beneficial to do so.

Frequency Utilization Lack of available frequencies and frequency congestion are quite often linked to increased controller/pilot workload and operational errors (i.e., safety), and to degradation in airspace capacity. The objective of this part of the study was to quantify the benefits of the CPDLC deployment in the integrated URET/CPDLC environment as a means to reduce frequency

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utilization. Hence, frequency utilization was computed in 5-minute intervals for one basic and two alternative scenarios, as presented in figure 6. Under the basic scenario, the level of frequency utilization was estimated for all communication messages using the voice-tape. Under the second scenario, the messages for (1) transfer of communication, (2) initial contact, and (3) altimeter setting were removed, as under CPDLC Build I, and the corresponding frequency utilization was computed. In the third scenario, non-time critical messages issued to solve aircraft conflicts were also removed. These messages included all non-time critical horizontal and vertical clearances, and speed assignments used to solve conflicts, as indicated in the CPDLC Build IA Phase, and previously explained in this study. The benefits gained from removing messages that corresponded to the CPDLC Build I and Build IA Phases were very evident, as indicated in figure 6. Reductions in frequency utilization were highest during the busy periods. For example, the highest 5-minute frequency utilization (52%) was found between 20:05 - 20:10 pm, which corresponded to the first traffic peak (20:00 - 20:15 pm). The frequency utilization was reduced to 38% after the secondscenario messages were removed, and to 22% under scenario 3. During another high traffic period (which included the highest number of conflicts), frequency utilizations were 38% under the baseline scenario, 24% under scenario 2, and 13% under scenario 3. Hence, a significant reduction in frequency utilization could be achieved not only on average, but more importantly during the busy periods. If non-time critical conflict messages were transmitted in the integrated CPDLC/URET environment, they could bring significant reduction in frequency utilization, particularly during busy periods with many conflicts.

Correlations among the Number of Aircraft in Sector, Number of Aircraft Conflicts, Number of Communication Messages, and Number of URET Alerts Figure 7 shows a very strong relation among all four measures. In general, all four measures have high positive correlations and similar trends. The average number of aircraft in the sector per 15-minute intervals was as low as 2 aircraft and as high as 11, although at one instant there were 14 aircraft in the sector. The average number of aircraft conflicts was as high as 16, between 19:15 – 19:30 pm. It is important to point out that URET’s highest average number of alerts was 18, which occurred during the same period. The average number of communication messages per 15-minute intervals closely followed these two trends, and were as low as 36, and as high as 121. The high correlations suggest that reasonable estimates for conflicts, communication activity, and URET alerts may be based on the number of aircraft in a sector (Table 3).

Analysis of Messages by Complexity and Type In addition to exploring the specific questions related to communicating conflict resolution messages via data link, we also used our data to develop a more general picture of voice communication activity in Sector 91. These analyses provide additional insight about the benefits that may result of CPDLC implementation.

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First, we found that there is essentially a one-to-one correspondence between controllerissued (49.83%) and pilot-issued (50.15%) messages (Table 4a). This result, while not surprising, assures us that the reduction in total voice traffic will be proportional to the reduction in controller-issued messages. We also found that most messages are simple when analyzed using the complexity analysis methods developed by Cardosi (1993) and Foushee (1986). As shown in table 4b, 84% of the messages contained only one element. This is important since it is difficult to project the extent to which multi-element messages would be off-loaded to CPDLC. Finally, we noted that about 10-15% percent of messages are the result of call backs, misunderstandings, and other consequences of errors in voice communication. Some of these messages would be avoided under CPDLC, either because the message resulting in the error does not occur, or because, as a result of reduced frequency congestion, the incidence of errors is decreased. In this respect, our estimates of the impact of CPDLC on voice traffic are conservative.

CONCLUSIONS AND RECOMMENDATIONS Our pilot study reveals that, for Sector 91 in the Indianapolis ARTCC, integrating CPDLC and URET would have significant benefits, particularly during peak traffic periods. It would be feasible to communicate conflict resolution messages using CPDLC in the integrated environment. More specifically, a majority of the conflict resolution messages observed were non-time critical so that they could be received in time to avoid loss of safety margins. If the non-time critical conflict messages were transmitted via data link in the integrated CPDLC/URET environment, they could bring considerable improvements to the frequency congestion/utilization. More importantly, the largest benefits would be felt in situations that involve a large number of aircraft conflicts, or during busy periods of traffic. These improvements could further help reduce the number of communication errors (and the consequent ATC workload), as well as the number of operational errors. It is recommended that the future studies involve analysis of a relationship between (a) volume/capacity and (b) frequency utilization trying to quantify the amount of capacity that can be obtained if the frequency congestion was lower. The study also recommends introduction of new MOPs for the integrated URET-CPDLC environment, such as the value A (time between controller’s clearance (t3) and URET alert notification (t1)), and value B (time difference between URET-predicted conflict start (t4) and controller’s clearance time (t3)). In addition, the future research should be conducted on the impact that transferring verbal communication to digital communication might have on the flight crew workload and on the air traffic controller workload. As a result of over 15 years of human factors studies, the user interface for CPDLC has been designed with good human factors standards. The Data Link Branch of the Communications, Navigation, and Surveillance Engineering Division at the William J. Hughes Technical Center extensively worked on reducing the workload associated with composing, sending, and responding to messages, and on minimizing the heads-down time required to use CPDLC. However, future research should explore how much the use of CPDLC will change the distribution of workload from both visual and aural to a primarily visual modality.

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ACKNOWLEDGMENTS The research underlying this paper was funded by the Federal Aviation Administration (FAA) and was conducted by the National Center of Excellence for Aviation Operations Research (NEXTOR). The opinions expressed in this paper are those of the authors, and responsibility for all errors remains with them. The authors wish to express their gratitude to the FAA for the financial support, and in particular to Michael Burski of the Office of Air Traffic Systems Development, the En Route Integrated product Team (AUA-200). Special thanks are also due to Alvin McFarland of the MITRE Corporation for his tireless supports. He provided the useful guidance, data and the software necessary for completing this research. We would also like to thank Ed Freeman of Dimensions International, Incorporated for his assistance in transcribing the voice tapes.

REFERENCES Brudnicki, D. J., A. L. McFarland and S. M. Schultheis. Conflict Probe Benefits to Controllers and Users: Indications from Field Evaluations, MITRE, MP96W0000194, 1996. Brudnicki, D. J., and A. L. McFarland. User Request Evaluation Tool (URET) Conflict Probe Performance and Benefits Assessment, MITRE, MP97W0000112, 1997. Cardosi, K. M. et al. An Analysis of En Route Controller-Pilot Voice Communications, Volpe NTSC, DOT/FAA/RD-93/11, 1993. Foushee, H. C. et al. Crew Factors in Flight Operations: III. The Operational Significance of Exposure to Short-haul Air Transport Operations, NASA, NASA Technical Memorandum 88322, 1986. Human Factors Task Force. Human Factors Requirements for Data Link, RTCA Paper No. 75492/SC-169-194, RTCA, 1992. Kerns, K. User Request Evaluation Tools (URET)/Controller Pilot Data Link Communications (CPDLC) Co-location: Development of and Operations Concept, Identification of Potential Issues, and Recommended Solution, 2001. Kerns, K. and A. L. McFarland. Conflict Probe Operational Evaluation and Benefits Assessment, MITRE, MP 98W0000239, 1998. Rehmann, A. Human Factors Recommendations for Airborne CPDLC Systems: A Synthesis of Research Results and Literature, Federal Aviation Administration, Report No. FAA/CT-TN97/6, 1997. Smolensky, M. W. and E. S. Stein. Human Factors in Air Traffic Control, Academic Press, 1998. Winokur, D.J. User Request Evaluation Tool (URET): Delivery 3.3 Training Materials, MITRE, MTR 00W000099, 2000.

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LIST OF TABLES 1

Models and Software Used in the Study

2

URET Output for Aircraft TWA388 Alerts in Sector 91

3

Correlations among Number of Communication Messages, Aircraft in Sector 91, Aircraft URET Alerts, and Conflicts per 15-minute Intervals

4

Message Analysis

LIST OF FIGURES 1

Study Area: Sector 91

2

Methodology: Information Flow, Relations among Models, and Measures of Performance (MOPs).

3

Relevant Times

4

URET and XEVAL Conflict Display for Three Aircraft

5

Time Difference between (a) Controller’s Clearance and URET Alert Notification (t3 - t1), (b) Controller’s Clearance and Aircraft Checking-in (t3 – t2) and (c) URET-predicted Conflict Start and Controller’s Clearance (t4 – t3)

6

Comparison of Voice Channel Frequency Utilization in 5-minute Intervals, Sector 91

7

Number of Communication Messages, Aircraft in Sector 91, Aircraft URET Alerts, and Conflicts per 15-minute Intervals

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TABLE 1 Models and Software Used in the Study

Transcriber

Reproducer

XEVAL

URET

Software for transcribing controller-pilot communication messages. Final outcome: (i) communication messages and (ii) start time of each message A 60-channel tape recorder/player. It is used for generating/recording voice messages. Used for assigning communication message times into Transcriber. Software for aircraft traffic and conflict analysis. It is used for the analysis of all clearance messages to determine if the message (recorded by Reproducer and written down by Transcriber) was a CONFLICT or a ‘regular’ CLEARANCE. Used for traffic analysis and for aircraft conflict prediction. Its data base is used for determining the earliest time of the conflict start time.

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TABLE 2 URET Output for Aircraft TWA388 Alerts in Sector 91 Notification Time t1 = 85038 185139 185315 185424 185438 185526 185546 t2 = 185821 t3 = 185931 185837 185854 190201

Aircraft ID 1

Aircraft ID 2

Color

Action

Reason

Conflict Start Time

TWA338 AAL1198 M_YELLOW ADD n/a 190428 TWA338 AAL1198 M_YELLOW UPD SMALL_CHG 190429 TWA338 AAL1198 M_YELLOW UPD SMALL_CHG 190428 TWA338 AAL1198 YELLOW UPD SIGNIF_CHG 190429 TWA338 AAL1198 M_YELLOW UPD SMALL_CHG 190429 TWA338 AAL1198 M_RED UPD SIGNIF_CHG 190400 TWA338 AAL1198 M_YELLOW UPD SMALL_CHG t4= 190348 (inserted value: derived from the controller-pilot communication messages) (inserted value: derived from the controller-pilot communication messages) TWA338 AAL1198 M_YELLOW UPD SMALL_CHG 190350 TWA338 AAL1198 YELLOW UPD SIGNIF_CHG 190350 TWA338 AAL1198 YELLOW DEL n/a 190350

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I91 I91 I91 I91 I91 I91 I91

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TABLE 3 Correlations among Number of Communication Messages, Aircraft in Sector 91, Aircraft URET Alerts, and Conflicts per 15-minute Intervals

Correlation Number of Aircraft in Sector Number of Conflicts Number of Messages Number of URET Alerts

Number of Aircraft In Sector

Number of Conflicts

Number of Messages

Number of URET Alerts

1 0.581

1

0.669

0.666

1

0.527

0.745

0.574

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TABLE 4 Message Analysis

(a) Basic Distribution of Messages

Pilots Controllers Total

Number of Messages 605 601 1206

%(total)

Number of Messages 1018 146 17 10 6 6 3 1206

% (total) 84.41 12.11 1.41 0.83 0.50 0.50 0.25 100.00

50.17 49.83 100.00

(b) Message Complexity

Message Complexity 1 element 2 elements 3 elements 4 elements 5 elements 6 elements 7 elements Total

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

15

Rakas, Hansen, Jirajarupon and Bolic

Indianapolis Center Super High-Altitude Sector 91

Memphis Center

FIGURE 1 Study Area: Sector 91.

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

16

Rakas, Hansen, Jirajaruporn and Bolic

RECORDER

TRANSCRIBER Data from the Host Computer Excel file with transcribed ATC messages (Table 2)

Analysis and selection of ATC messages that ‘looked’ like conflicts.

MOPs: 1. time pilot checks into the system (t2) 2. time controller issued a clearance (t3) 3. message type 4. message duration 5. number of messages 6. aircraft type 7. frequency utilization (congestion)

URET

Identification of conflict situations corresponding to ATC transcribed messages that ‘looked’ like conflicts.

MOPs: 1. URET earliest alert time (t1) 2. URET-predicted conflict start time (t4) 3. total number of controlled aircraft in sector per unit time 4. number of URET alerts

XEVAL

Analysis of aircraft conflicts, changes in route amendments.

MOPs: 1. aircraft conflict profile (horizontal or vertical) 2. number of aircraft in conflict (two or more)

Verify conflict

MOPs: A = t3 - t1 = time between controller’s clearance and URET’s first conflict notification B = t4 - t3 = time between URET-predicted conflict start time and controller’s clearance C = t3 - t2 = time between controller’s clearance and the first time aircraft checks in.

FIGURE 2 Methodology: Information Flow, Relations among Models, and Measures of Performance (MOPs).

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

17

Rakas, Hansen, Jirajaruporn and Bolic

C

B

A

t1 t1 = t2 = t3 = t4 =

t2

t3

t4

first time URET has notified a conflict, which will occur at t4 time aircraft (pilot) checked into the sector controller issued a clearance URET-predicted conflict start time

A = t3 - t1 = time between controller’s clearance and URET’s first conflict notification B = t4 - t3 = time between URET-predicted conflict start time and controller’s clearance C = t3 - t2 = time between controller’s clearance and the first time aircraft checks in FIGURE 3 Relevant Times.

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

18

Rakas, Hansen, Jirajaruporn and Bolic

(a) URET Conflict Display for Three Aircraft

(b) Vertical Conflict Analysis for Three Aircraft

FIGURE 4 URET and XEVAL Display for Three Aircraft.

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

21

Rakas, Hansen, Jirajaruporn and Bolic

12

900

800 10 700

seconds

500 6 400

4

300

200 2 100

0

0

45 22:

:30 22

:15 22

:00 22

:45 21

30 21:

:15 21

:00 21

:45 20

30 20:

15 20:

00 20:

:45 19

30 19:

15 19:

:00 19

:45 18

:30 18

:15 18

:00 23

:45 22

:30 22

:15 22

:00 22

45 21:

:30 21

:15 21

:00 21

45 20:

:30 20

:15 20

:00 20

45 19:

:30 19

:15 19

:00 19

:45 18

:30 18

Time(hours) average t3-t1(secs) per 15 minutes

average t4-t3(secs) per 15 minutes

t3-t2(secs) per 15 minutes

Number of Aircraft in Sector 91 per 15 minutes

FIGURE 5 Time Difference between (a) Controller’s Clearance and URET Alert Notification (t3 - t1), (b) Controller’s Clearance and Aircraft Checking-in (t3 – t2) and (c) URET-predicted Conflict Start and Controller’s Clearance (t4 – t3).

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

aircraft

8

600

18 :4 5: 18 00 :5 5: 18: 50 19 00 - 1 :00 :0 5: 9: 00 19 00 :0 :1 1 5: 9: 0 0 1 0 19 0 - 1 :00 :2 5: 9: 20 19 00 :0 :3 1 5: 9: 0 0 3 0 19 0: 0 :4 5: 19: 0 0 4 0 19 0: 0 :5 5: 19: 0 0 5 0 20 0: 0 :0 5: 20: 0 0 0 0 20 0: 0 :1 5: 20: 0 0 1 0 20 0: 0 :2 5: 20: 0 0 2 0 20 0: 0 :3 5: 20: 0 0 3 0 20 0: 0 :4 5: 20: 0 0 40 0 20 - 2 :00 :5 5: 0: 50 21 00 :0 :0 2 5: 1: 0 0 0 0 21 0 - 2 :00 :1 5: 1: 10 21 00 :0 :2 2 5: 1: 0 0 2 0 21 0: 0 :3 5: 21: 0 0 3 0 21 0: 0 :4 5: 21: 0 0 4 0 21 0: 0 :5 5: 21: 0 0 5 0 0: 22 0 :0 5: 22: 0 0 0 22 0 0: 0 :1 5: 22: 0 10 22 00 - 2 :00 :2 5: 2: 20 22 00 :0 :3 2 5: 2: 0 30 22 00 - 2 :00 :4 5: 2: 40 22 00 :0 :5 2 0 5: 2 00 :50 - 2 :00 3: 00 :0 0

Frequency Utilization (%)

Rakas, Hansen, Jirajaruporn and Bolic

TRB 2003 Annual Meeting CD-ROM

22

60

50

Frequency utilization in 5-minute intervals for all meesages (% time) Frequency utilization in 5-minute intervals without CPDLC Build 1 messages (% time) Frequency utilization in 5-minute intervals without non-time critical conflict messages and CPDLC Build 1 (% time)

40

30

20

10

0

Time (hours)

FIGURE 6 Comparison of Voice Channel Frequency Utilization in 5-minute Intervals, Sector 91.

Paper revised from original submittal.

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Rakas, Hansen, Jirajaruporn and Bolic

120

100

80

60

40

20

0

5 :4 22

0 :3 22

5 :1 22

0 :0 22

5 :4 21

0 :3 21

5 :1 21

0 :0 21

5 :4 20

0 :3 20

5 :1 20

0 :0 20

5 :4 19

0 :3 19

5 :1 19

0 :0 19

5 :4 18

0 :3 18

5 :1 18

Number of Aircraft in Sector 91 per 15 minutes

Number of Conflicts per 15 minutes (t1)

Number of messages per 15 minutes

Number of URET alerts per 15 minutes

FIGURE 7 Number of Communication Messages, Aircraft in Sector 91, Aircraft URET Alerts, and Conflicts per 15-minute Intervals.

TRB 2003 Annual Meeting CD-ROM

Paper revised from original submittal.

00 3: -2

45 2: -2

30 2: -2

15 2: -2

00 2: -2

45 1: -2

30 1: -2

15 1: -2

00 1: -2

45 0: -2

30 0: -2

15 0: -2

00 0: -2

45 9: -1

30 9: -1

15 9: -1

00 9: -1

45 8: -1

30 8: -1

Time (hours)