Detect & Avoid Alerting Logic for UnmannedSystems1

Cesar MunozNASA Langley Research Center

Dagstuhl Seminar: Qualification of FM ToolsApril 28, 2015

1The DAIDALUS logo was designed by M. Malekpour.

https://ntrs.nasa.gov/search.jsp?R=20160007330 2018-07-29T01:21:40+00:00Z

See and AvoidMichael Huerta, Administrator, Federal Aviation Administration:2

A bedrock principle of aviation is see and avoid. And ifyou don’t have a pilot on board the aircraft, you needsomething that will substitute for that, which will senseother aircraft, and we can ensure appropriate levels ofsafety.

2http://www.pbs.org/newshour/bb/

drone-industry-grows-faster-flick-joystick-regulation-lag.2 / 22

Detect and Avoid3

Detect and Avoid (DAA) was defined by the FAA sponsored SAAfor UAS (First) Workshop Final Report published in October 9,2009 as the combination of UAS Self-Separation (SS) plusCollision Avoidance (CA) as a means of compliance with 14CFRPart 91, §91.111 and §91.113.

3Formerly called Sense and Avoid.3 / 22

14CFR Part 91

I 91.111 (a) No person may operate an aircraft so close toanother aircraft as to create a collision hazard.

I 91.113 (b) General. When weather conditions permit,regardless of whether an operation is conducted underinstrument flight rules or visual flight rules, vigilance shall bemaintained by each person operating an aircraft so as tosee and avoid other aircraft. When a rule of this sectiongives another aircraft the right-of-way, the pilot shall give wayto that aircraft and may not pass over, under, or ahead ofit unless well clear.

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Requirements for DAA Concept

Concept shall . . .

I provide a geometric means to determine well-clear status,

I enable self-separation capabilities,

I avoid undue concern for traffic aircraft,

I interoperate with existing collision avoidance systems, e.g.,TCAS.

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Well Clear

I Two aircraft are well clear if appropriate distance and timevariables determined by their states remain outside a set ofpredefined threshold values.

I A well-clear violation occurs when:I horizontal range is less than DMOD or ( distance at time of

CPA is less than HMD and modified tau is less thanTAUMOD ) and

I relative altitude is less than ZTHR or time to co-altitude is lessthan TCOA.

I Concrete values for threshold values is matter of on-goingresearch. Current values by poposed by the Sense and AvoidScience Research Panel (SARP): HMD = DMOD = 4000 ft,TAUMOD = 35 s, ZTHR = 450 ft, and TCOA = 0 s.

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Well-Clear Violation VolumeTop View of an Example Encounter

−8 −6 −4 −2 0 2 4−3.5

−3

−2.5

−2

−1.5

−1

−0.5

0

0.5

x (nmi)

y (

nm

i)

WC_TAUMOD = 6.1 square nmi

Intruder

Ownship

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Well-Clear Properties

I Inclusion: For an appropriate choice of threshold values, thewell-clear violation volume is larger than the TCAS volume.

I Symmetry: In a pair-wise situation, both aircraft make thesame determination about their well-clear status.

I Local Convexity: In a non-maneuvering trajectory, there is atmost one time interval where the aircraft are in well-clearviolation.

These properties were . . .

I proposed by the FM group at NASA LaRC and formallyverified in the Prototype Verification System (PVS) for afamily of well-clear concepts,

I considered to be necessary conditions by SARP for anywell-clear definition, and

I helped to discard 2 of 3 proposed definitions of the well-clearviolation volume.

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DAIDALUSDetect and Avoid Alerting Logic for Unmanned Systems

I DAIDALUS is an implementation in Java, C++, and PVS,developed by the FM group at NASA LaRC, of SARP’s DAAconcept.

I DAIDALUS provides algorithms forI Checking and predicting loss of well clear (1×1)I Computing alert level (1×1)I Computing conflict and recovery bands (1×n)

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What’s in a Name?

I DAIDALUS is a reference to the craftsman of Greekmythology, Daedalus, the father of Icarus.

I Daedalus made wings for himself and for Icarus and warnedIcarus not to fly too high, because the heat of the sun wouldmelt the wax, nor too low, because the sea foam would soakthe feathers.

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4Image taken from http://en.wikipedia.org/wiki/Daedalus.10 / 22

Well-Clear Algorithms: Time To Violation

I Given ownship and intruder state information and a lookaheadtime, return the time interval of well-clear violation assumingnon-maneuvering trajectories.

I Return the empty interval when aircraft are not predicted tobe in well-clear violation within the lookahead time.

I Return an interval that contains 0 (current time) whenaircraft are currently in well-clear violation.

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Well-Clear Algorithms: Conflict Bands

I Given ownship and traffic state information and a lookaheadtime, compute ranges of track, ground speed, vertical speed,and altitude that lead to well-clear violation within lookaheadtime. . .

I . . . assuming a kinematic trajectory for the ownship andnon-maneuvering trajectories for the traffic aircraft.

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Preventive BandsBands outside current trajectory of the aircraft:

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Corrective BandsBands in current trajectory of the aircraft:

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Recovery Bands

Aircraft are (about to be) in well-clear violation:

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Well-Clear Algorithms: Alerting Logic

I Given ownship and intruder state information, return an alertlevel (numerical value) indicating severity of potential loss ofwell clear.

I Two alerting schemas are supported (matter of on-goingresearch):

I Thresholds-based.I Bands-based.

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Research Outcomes

I Mathematical definition (in PVS) of a family of well-clearconcepts.

I Formally verified algorithms (in PVS) for maintainingwell-clear and recovering from well-clear losses.

I Software implementations (in Java and C++) of SARP’swell-clear concept released under NASA’s Open SourceAgreement.

DAIDALUS has been tested in flight experiments conducted underNASA’s UAS in the NAS Project.

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Unexpected Outcomes

I DAIDALUS is being considered for inclusion as DAA referenceimplementation in the appendix of RTCA Special Committee228 Minimum Operational Performance Standards (MOPS)for Unmanned Aircraft Systems. Ref. Don Walker (FAA).

I DAIDALUS is being considered by FAA Tech Center for flighttest study to determine the minimum pilot interfacerequirements for DAA. Ref. Kevin Williams (FAA).

I Mathematical framework was used in the development of SAAconcept by General Atomics Aeronautical Systems (GA-ASI).Ref. Brandon Suarez (GA).

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On-Going Work

I Validation of software implementation against formal models:I Test cases are automatically generated.I Software outputs are checked against outputs of executable

formal models for different degrees of accuracy.

I Validation of software implementation against performancemetrics.

I What is a stressing case?

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References (I)

I C. Munoz, A. Narkawicz, G. Hagen, J. Upchurch, A. Dutleand M. Consiglio, Detect & Avoid Alerting Logic forUnmanned Systems (DAIDALUS), submitted 2015.

I J. Upchurch, C. Munoz, A. Narkawicz, M. Consiglio, and J.Chamberlain, and M. Consiglio, Characterizing the Effects ofa Vertical Time Threshold for a Class of Well-ClearDefinitions, submitted, 2015.

I J. Upchurch, C. Munoz, A. Narkawicz, J. Chamberlain, andM. Consiglio, Analysis of Well-Clear Boundary Models for theIntegration of UAS in the NAS, Technical Memorandum,NASA/TM-2014-218280, June 2014.

I C. Munoz, A. Narkawicz, J. Chamberlain, M. Consiglio, and J.Upchurch, A Family of Well-Clear Boundary Models for theIntegration of UAS in the NAS, Proceedings of the 14th AIAAAviation Technology, Integration, and Operations (ATIO)Conference, AIAA-2014-2412, Atlanta, Georgia, 2014.

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References (II)

I A. Narkawicz, C. Munoz, J. Upchurch, J. Chamberlain, andM. Consiglio, A Well-Clear Volume Based on Time to EntryPoint, Technical Memorandum, NASA/TM-2014-218155,January 2014

I C. Munoz, A. Narkawicz, and J. Chamberlain, A TCAS-IIResolution Advisory Algorithm, Proceedings of the AIAAGuidance, Navigation, and Control Conference (GNC),AIAA-2013-4622, Boston, Massachusetts, August 2013.

I M. Consiglio, J. Chamberlain, C. Munoz, and K. Hoffer,Concept of integration for UAS operations in the NAS,Proceedings of the 28th International Congress of theAeronautical Sciences (ICAS 2012), 2012.

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Software Releases Under NASA’s Open Source Agreement

I ACCoRD ⊆ Bands ⊆ Chorus ⊆ Stratway:http://shemesh.larc.nasa.gov/fm/fm-at-codes.html.

I Well-Clear: http://github.com/nasa/WellClear.

I DAIDALUS ⊆ Stratway ∪ Well-Clear.

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