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Evaluation of proposed changes to the ACAS modified tau calculation

May 1, 2006
  |
Conference Paper
Author:
James K. Kuchar
Published in:
Int. Civil Aviation Organization Aeronautical Surveillance Panel Working Group, 1 May 2006.
Topic:
collision avoidance
R&D area:
R&D group:

Summary

Modified tau is a parameter computed by ACAS to estimate the earliest time at which a collision could occur should an intruder aircraft accelerate toward the own aircraft. A concern with the modified tau calculation has been raised in a class of encounters where intruders are already close and converging slowly. In these problem cases, ACAS may induce a Near Mid-Air Collision by generating RAs with inappropriate timing or initial sense or failing to reverse sense when necessary. Performance in some problem encounters is greatly improved when using several proposed changes to the modified tau equations. These changes are outside CP112E, which focuses only on RA reversals. Although changes to modified tau resolve some problem encounters, aggregate risk-ratio results do not support implementing the existing proposals. There remains a concern about mid-air collision risk due to vulnerability in the existing modified tau equations, yet a robust solution to the problem has not been developed.
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Summary

Modified tau is a parameter computed by ACAS to estimate the earliest time at which a collision could occur should an intruder aircraft accelerate toward the own aircraft. A concern with the modified tau calculation has been raised in a class of encounters where intruders are already close and converging...

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Evaluation of proposed changes to the ACAS modified tau calculation

Update on the analysis of ACAS performance on Global Hawk

May 1, 2006
  |
Conference Paper
Author:
James K. Kuchar
Published in:
Int. Civil Aviation Organization Aeronautical Surveillance Panel Working Group, 1 May 2006.
Topic:
UAVs
R&D area:
R&D group:

Summary

Initial results are presented from a Lincoln Laboratory study of ACAS performance on the Global Hawk UAV. The study has been applying the process outlined in the ICAO ACAS Manual which involves developing UAV airspace encounter models and running fast-time Monte Carlo simulations of encounters. ACAS performance was examined in conventional aircraft vs. conventional aircraft, conventional aircraft vs. non-ACAS Global Hawk, and conventional aircraft vs. ACAS-equipped Global Hawk cases. The existing ICAO and ACASA encounter models were modified to reflect Global Hawk flight characteristics. ACAS performance on Global Hawk was also assessed parametrically across reaction latencies from 0 - 20 s. Global Hawk flight characteristics were shown to have a small but measurable negative impact on collision risk. Assuming no system failures or visual acquisition effects occur, performance with ACAS on Global Hawk is significantly better than without ACAS if response latencies (from the moment an RA is issued to the moment maneuvering begins) are less than 10 s. Performance drops off rapidly at latencies greater than 10 s. The needs for improved airspace models and a more in-depth study of the interaction between visual acquisition and ACAS are noted.
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Summary

Initial results are presented from a Lincoln Laboratory study of ACAS performance on the Global Hawk UAV. The study has been applying the process outlined in the ICAO ACAS Manual which involves developing UAV airspace encounter models and running fast-time Monte Carlo simulations of encounters. ACAS performance was examined in...

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Update on the analysis of ACAS performance on Global Hawk

Safety analysis methodology for unmanned aerial vehicle (UAV) collision avoidance systems

June 27, 2005
  |
Conference Paper
Author:
James K. Kuchar
Published in:
USA/Europe Air Traffic Management Seminar, 27-30 June 2005.
Topic:
collision avoidance
R&D area:
R&D group:

Summary

The integration of Unmanned Aerial Vehicles (UAVs) into civil airspace requires new methods of ensuring collision avoidance. Concerns over command and control latency, vehicle performance, reliability of autonomous functions, and interoperability of sense-and-avoid systems with the Traffic Alert and Collision Avoidance System (TCAS) and Air Traffic Control must be resolved. This paper describes the safety evaluation process that the international community has deemed necessary to certify such systems. The process focuses on a statistically-valid estimate of collision avoidance performance developed through a combination of airspace encounter modeling, fast-time simulation of the collision avoidance system across millions of encounter scenarios, and system failure and event sensitivity analysis. Example simulation results are provided for an implementation of the analysis process currently being used to evaluate TCAS on the Global Hawk UAV.
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Summary

The integration of Unmanned Aerial Vehicles (UAVs) into civil airspace requires new methods of ensuring collision avoidance. Concerns over command and control latency, vehicle performance, reliability of autonomous functions, and interoperability of sense-and-avoid systems with the Traffic Alert and Collision Avoidance System (TCAS) and Air Traffic Control must be resolved...

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Safety analysis methodology for unmanned aerial vehicle (UAV) collision avoidance systems

Remotely piloted vehicles in civil airspace: requirements and analysis methods for the traffic alert and collision avoidance system (TCAS) and see-and-avoid systems

October 24, 2004
  |
Conference Paper
Author:
Ann C. Drumm
…
Published in:
Proc. of the 23rd Digital Avionics Systems Conf., DASC, Vol. 2, 24-28 October 2004, pp. 12.D.1-1 - 12.D.1.14.
Topic:
air traffic control
R&D area:
R&D group:

Summary

The integration of Remotely Piloted Vehicles (RF'Vs) into civil airspace will require new methods of ensuring aircraft separation. This paper discusses issues affecting requirements for RPV traffic avoidance systems and for performing the safety evaluations that will be necessary to certify such systems. The paper outlines current ways in which traffic avoidance is assured depending on the type of airspace and type of traffic that is encountered. Alternative methods for RPVs to perform traffic avoidance are discussed, including the potential use of new see-and-avoid sensors or the Traffic Alert and Collision Avoidance System (TCAS). Finally, the paper outlines an established safety evaluation process that can be adapted to assure regulatory authorities that RPVs meet level of safety requirements.
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Summary

The integration of Remotely Piloted Vehicles (RF'Vs) into civil airspace will require new methods of ensuring aircraft separation. This paper discusses issues affecting requirements for RPV traffic avoidance systems and for performing the safety evaluations that will be necessary to certify such systems. The paper outlines current ways in which...

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Remotely piloted vehicles in civil airspace: requirements and analysis methods for the traffic alert and collision avoidance system (TCAS) and see-and-avoid systems

Safety analysis process for the Traffic Alert and Collision Avoidance System (TCAS) and see-and-avoid systems on remotely piloted vehicles

September 20, 2004
  |
Conference Paper
Author:
James K. Kuchar
…
Published in:
AIAA 3rd Unmanned-Unlimited Technical Conf., 20-23 September 2004, pp. 1-13.
Topic:
collision avoidance
R&D area:
R&D group:

Summary

The integration of Remotely Piloted Vehicles (RPVs) into civil airspace will require new methods of ensuring traffic avoidance. This paper discusses issues affecting requirements for RPV traffic avoidance systems and describes the safety evaluation process that the international community has deemed necessary to certify such systems. Alternative methods for RPVs to perform traffic avoidance are discussed, including the potential use of new see-and- avoid sensors or the Traffic Alert and Collision Avoidance System (TCAS). Concerns that must be addressed to allow the use of TCAS on RPVs are presented. The paper then details the safety evaluation process that is being implemented to evaluate the safety of TCAS on Global Hawk. The same evaluation process can be extended to other RPVs and traffic avoidance systems for which thorough safety analyses will also be required.
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Summary

The integration of Remotely Piloted Vehicles (RPVs) into civil airspace will require new methods of ensuring traffic avoidance. This paper discusses issues affecting requirements for RPV traffic avoidance systems and describes the safety evaluation process that the international community has deemed necessary to certify such systems. Alternative methods for RPVs...

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Safety analysis process for the Traffic Alert and Collision Avoidance System (TCAS) and see-and-avoid systems on remotely piloted vehicles

Modifications to ACAS safety study methods for remotely piloted vehicles (RPV)

May 3, 2004
  |
Conference Paper
Author:
James K. Kuchar
Published in:
Int. Civil Aviation Organization Surveillance and Conflict Resolution Systems Panel Working Group, 3-7 May 2004.
Topic:
UAVs
R&D area:
R&D group:

Summary

Estimating the relative safety of a Remotely Piloted Vehicle (RPV) equipped with ACAS will require several extensions to the methods developed in previous ACAS studies. This paper outlines several of these redesign issues. First, it may be necessary to compute the probability that an RPV will experience a critical encounter relative to that for a conventional aircraft. Performing a safety study on only the incremental impact of equipping an RPV with ACAS would circumvent this need. Additionally, methods are proposed to adapt existing encounter models to better represent the likely characteristics of encounters with RPVs. Finally, modifications to the level of detail included in dynamic simulations and fault trees are discussed. It is proposed to shift all dynamic elements out of the fault tree and into a new more complex Monte Carlo simulation.
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Summary

Estimating the relative safety of a Remotely Piloted Vehicle (RPV) equipped with ACAS will require several extensions to the methods developed in previous ACAS studies. This paper outlines several of these redesign issues. First, it may be necessary to compute the probability that an RPV will experience a critical encounter...

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Modifications to ACAS safety study methods for remotely piloted vehicles (RPV)
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