1. Regaining Lost Separation in a Piloted Simulation of Autonomous Aircraft Operations
Richard Barhydt* Dr. Todd Eischeid† Michael Palmer* David Wing* *NASA Langley Research Center, Hampton VA USA †Booz-Allen & Hamilton, Hampton VA USA

2. Distributed Air/Ground Traffic Management (DAG-TM)
Aeronautical Operational Control
Air Traffic Service Provider
Flight Crew
Information
Decision making
Responsibility
NASA working on new concept of operations (DAG-TM): designed to improve system capacity, airspace user flexibility, and user efficiency through
Sharing information related to flight intent, traffic, and the airspace environment
Collaborative decision making among all involved system participants
Distributing decision authority to the most appropriate decision maker
System must be scalable: an increase in the number of aircraft must be accompanied by an equivalent increase in traffic management capability. The current centralized control paradigm has problems here: as traffic capacity goes up, there must be either an increase in capability per sector or there must be more sectors. The more-sectors approach quickly reaches its limits because of inter-sector coordination issues. More capability per sector is limited by the human controller. As long as we want a human-centered system, the best route to a scalable system is distribution of authority and responsibility.
We have no preconceived notions that the distributed nature alone will result in peak capacity. Although there are plenty of arguments that increased flexibility results in a more optimal system (the free economy vs. planned economy argument), DAG-TM puts much emphasis on a centralized ground-based system doing flow management. Current ideas in flow management include advanced concepts in slot allocation and a move away from an asynchronous (“first-come first-served”) system. Free flight works with these ideas to make the imposed constraints more easily met.
Richard Barhydt, NASA Langley Research Center

3. DAG-TM Flight Operations
Autonomous Aircraft
Onboard Airborne Separation Assurance System that enables flight crew to resolve traffic conflicts with autonomous and managed aircraft and special use airspace.
Allowed to freely maneuver subject to not creating near-term conflicts and complying with flow management constraints.
Managed Aircraft
Not equipped for autonomous operations.
Separation from other managed aircraft provided by Air Traffic Service Provider (ATSP).
ATSP continues to provide flight path constraints to all aircraft as needed to meet local traffic flow management needs.
Richard Barhydt, NASA Langley Research Center

4. Airborne Separation Assurance System (ASAS)
Prototype system developed at NASA Langley consists of conflict detection, prevention, and resolution.
Normally allows safe conflict resolution long before hazard to safe flight created.
Non-normal events could require pilots to resolve near-term conflicts and regain lost separation.
ASAS must provide effective resolution guidance prior to when TCAS issues Resolution Advisory.
Richard Barhydt, NASA Langley Research Center

5. Potential Reduction in Separation Minimums
NASA interested in conducting feasibility studies looking into potential reduction in separation minimums.
Studies suggest lower minimums likely needed to improve capacity.
Current minimums trace back to limitations of older radar systems.
Considerations for lowering separation minimums.
Surveillance system performance – accuracy, integrity, availability.
Presence of flight technical errors.
Appropriate pilot maneuver response when confronted with near-term conflict.
Richard Barhydt, NASA Langley Research Center

6. Experiment Goals
Experiment conducted in NASA Langley Air Traffic Operations Lab to address issues related to ASAS use during near-term conflicts and potential reduction in separation minimums.
Experiment goals:
Evaluate effectiveness of prototype ASAS tools in enabling pilots to safely resolve near-term conflicts.
Compare effects of 3 and 5 NM separation zone (with 1000 ft vertical separation) on pilot’s ability to resolve near-term conflicts and regain lost separation.
Richard Barhydt, NASA Langley Research Center

7. Experiment Design Air Traffic Operations Lab:
Medium fidelity PC workstation-based facility.
Capable of simultaneous operation by 8 subject pilots.
Pilot workstations have transport aircraft model.
Controls and displays designed to replicate MD-11.
Traffic information superimposed on Navigation Display.
Subjects: 16 commercial airline pilots with Airbus or MD-11 experience.
Design: single-factor within-subjects.
3 or 5 NM lateral separtion standard.
1000 ft vertical separation standard used for both cases.
Richard Barhydt, NASA Langley Research Center

8. Pilot Displays and Control Panels
Richard Barhydt, NASA Langley Research Center

9. Scenario Set-up and Pilot Tasks
All pilots flew autonomous aircraft in DAG-TM en route environment.
Pilots could maneuver freely without contacting controller.
Experiment focused on air-air separation assurance and did not include a ground component.
Pilots required to maintain required separation from other traffic and cross downstream waypoint at Required Time of Arrival (RTA).
Nominal flight path through 65 NM wide corridor with restricted areas on both sides.
Designed near-term conflict occurred 15 min into 25 min scenario.
Richard Barhydt, NASA Langley Research Center

10. Separation and Collision Zones
Based on work of RTCA Airborne Conflict Management Committee
Richard Barhydt, NASA Langley Research Center

11. Near-term Conflict Event
Designated intruder hidden from subject pilot until just before predicted loss of separation.
Intruder appeared about 6 NM away at co-altitude with ownship.
Pseudo pilots used to ensure designed conflict occurred even after possible previous maneuver by subject pilot.
Initial conflict geometry (location, approach angle, time to closest approach) designed to be same for both 3 and 5 NM separation zone cases.
Scenario differences between 3 and 5 NM cases:
Separation loss occurred earlier, but further from intruder for 5 NM separation zone case.
Designed to highlight any variation in pilot performance due to being inside or outside separation zone.
Richard Barhydt, NASA Langley Research Center

12. Pilot Displays when Intruder Appeared
Richard Barhydt, NASA Langley Research Center

13. ε as Measure of Threat Severity
3 NM
5 NM
1000 ft
ε = 0
ε = 1
Cross section of
5 NM Separation
Zone and Ellipsoid
Ellipsoid centered on intruder aircraft inscribed within cylindrical separation zone.
ε combines relative lateral and vertical distances between ownship and intruder, ε = 0 at center and ε = 1 at surface.
Has advantage over closest point of approach in that it normalizes lateral and vertical distance based on required separation.
Richard Barhydt, NASA Langley Research Center

14. Performance Metrics
Threat proximity (εmin): actual minimum ε between 2 aircraft.
Risk mitigation (εdiff): difference between predicted ε at time alert issued (based on current state of both aircraft) and εmin.
Accounts for any differences that may have occurred due to initial conflict geometry.
Predicted εmin at time alert issued varied from 0.01 to 0.07 with overall mean across all scenarios of 0.04.
εmin and εdiff calculated using 5 NM ellipsoid in order to compare results between 5 NM and 3 NM separation zones.
Richard Barhydt, NASA Langley Research Center

15. Threat Proximity
0.0
0.2
0.4
0.6
0.8
1.0
3 NM Separation
5 NM Separation
Epsilon
min
Complied with tactical guidance
Did not comply with tactical guidance
Note: Error bars represent 1 standard error of the mean.
n=13
n=3
n=6
n=9
Lateral separation zone size did not appear to affect threat proximity.
Greater separation between aircraft achieved when pilots followed tactical resolution guidance.
Linear regression of εmin for compliance combined across separation zone conditions shows significant differences at
 = 0.05 level.
Richard Barhydt, NASA Langley Research Center

16. εdiff does not appear to be affected by separation zone size.
Risk Mitigation
0.0
0.2
0.4
0.6
0.8
1.0
3 NM Separation
5 NM Separation
Epsilon
diff
Complied with tactical guidance
Did not comply with tactical guidance
Note: Error bars represent 1 standard error of the mean.
n=13
n=3
n=6
n=9
Shows same trends as threat proximity.
εdiff does not appear to be affected by separation zone size.
εdiff marginally larger when pilots complied with resolution guidance.
Linear regression of εdiff for compliance combined across separation zone conditions shows marginal differences
(p = 0.088) (not significant at  = 0.05 level).
Richard Barhydt, NASA Langley Research Center

17. Conclusions and Future Work (1/2)
Pilots performed better when they followed tactical resolution guidance.
In order to improve compliance rate, improvements are planned for ASAS in effort to provide better transition between ASAS and Airborne Collision Avoidance System (ACAS).
Incorporate TCAS design goals into tactical resolution guidance:
Attempt to avoid crossing intruder’s altitude.
Provide resolution that does not require ownship to change direction if currently maneuvering.
Allow time for each aircraft to initiate maneuver before changing sense of resolution advisory and only reverse sense if needed to ensure safety.
Richard Barhydt, NASA Langley Research Center

18. Conclusions and Future Work (2/2)
Results of this study suggest that maneuvering to avoid near term conflict is no more difficult when required lateral separation reduced to 3 NM.
Prior to reducing separation minimums, Operational Safety Assessment considering surveillance system performance and operational effects must be conducted.
Future studies will further investigate ASAS/ACAS integration.
Next major DAG-TM experiment will be joint study with Ames Research Center to look into mixed equipage operations, en route and terminal area procedures, and air/ground coordination.
Richard Barhydt, NASA Langley Research Center

19. Backup Slides
Richard Barhydt, NASA Langley Research Center

20. Tactical Conflict Detection and Resolution (CD&R)
Intruder protected zone
Minimum distance
1. Heading change
2. Speed change
Ownship
Avoidance vector
Advised vector
Not shown: 3. vertical speed change
Protected Zone radius = 5 nm ½h = 1000 ft
Intruder
Richard Barhydt, NASA Langley Research Center

21. Pilot Questionnaires
Question
Rating Scale
Overall Mean
How intuitive was the conflict alerting system?
1: not at all intuitive → 7: very intuitive
5.0
How acceptable were the tactical resolutions?
1: not at all acceptable → 7: completely acceptable
4.3
What was the level of safety for this scenario?
1: completely unsafe → 7: completely safe
4.0
How did the conflict management tools affect the risk level?
1: greatly increased risk → 7: greatly decreased risk
4.8
Pilots asked to rate decision support tools and perceived operational safety on scale from 1 (least favorable) to 7 (most favorable).
Richard Barhydt, NASA Langley Research Center

22. Richard Barhydt, NASA Langley Research Center

23. $,J Q Concept Integrates: Mixed equipage Operational constraints
Autonomous Aircraft
Air Traffic Service Provider
Managed Aircraft
Aeronautical Operational Control
$,J
Cost management,
Passenger comfort
Hazard avoidance
Concept Integrates:
Mixed equipage
User preferences
Operational constraints
Equipage priority
Separation
assurance
Fleet management
Terminal area
Crossing restrictions
Traffic flow
management
Priority
rules
Maneuver rules
Special Use
Airspace avoidance
Trajectory management
User-determined optimal trajectory
Richard Barhydt, NASA Langley Research Center