National Aeronautics and Space AdministrationNational Aeronautics and Space Administration
Ensuring Interoperability between Unmanned Aircraft Detect-and-Avoid and Manned Aircraft Collision
Avoidance
David ThipphavongAndrew ConeSeungman Lee
https://ntrs.nasa.gov/search.jsp?R=20180000588 2019-03-19T05:32:40+00:00Z
Introduction
2
• RTCASpecialCommittee-228isinchargeofdevelopingstandardsforDetect-and-Avoid(DAA)forUnmannedAircraftSystems(UAS)intheUnitedStates
• UASDAAsystemsenableUAStosatisfyregulationstoremainwellclearfromandavoidcollisionswithotherairbornetraffic
• UASDAAsystemsneedtointeroperatewithcollisionavoidance(CA)systemsonboardmannedaircraft– TrafficAlertandCollisionAvoidanceSystem(TCAS)intheUnited
States– AirborneCollisionAvoidanceSystem(ACAS)inEurope
UASDAAInteroperability
3
• AllRAsareverticalcommands
RTCASC-228’sApproach• RestrictUASDAAverticalguidancewhenUASandmanned
aircraftarewithinaCAregion:– NoUASaltitudeguidance– UASverticalspeedguidanceislimitedtoUAScurrentverticalspeed
± 500ft/min(Londner,ATM2015)
UASDAAsystemsmustnotprovideguidancethatisincompatiblewithResolutionAdvisories(RAs)thatmannedaircraftreceivefromtheircollisionavoidancesystem
ResearchOverview
4
ResearchGoal• EvaluateRTCASC-228’sCAregiondefinitioninthepreliminary
standardsdocumentintermsofinteroperabilitywithTCASRAsandDAAalerts
• Developalternativedefinitionsandevaluatetheirinteroperability
OutcomeRTCASC-228approvedanewdefinitionwerecommendedforthefinalstandardsdocument
CARegionInteroperability
5
DAA alert issued
timeCA region
crossedTCAS RA
issued
PreferredorderinencounterswithTCASRA
timeCA region
crossed
NotacceptablebecauseUASverticalmaneuvers
notrestricted
time
DAA alert issued
CA region crossed
TCAS RA issued
TCAS RA issued
NotacceptablebecauseUASverticalmaneuvers
notrestricted
timeMinimizefrequencyforinteroperabilitywithDAA
alerts
SummaryofCARegionInteroperability
6
DAA alert issued
timeTCAS RA
issued
Initial CA RegionCrossing
“Goldilocks”solution:Justright
timeTCAS RA
issued
Acceptable:Restrictleastoften
DAA alert issued
timeTCAS RA
issued
Initial CA RegionCrossing
Unacceptable:Restrictlate
DAA alert issued
Initial CA RegionCrossing
CollisionAvoidanceRegion
• ThreeCAregiondefinitioncandidatesevaluated
• HorizontalComponents:– HorizontalMissDistance(HMD):Projectedseparationatclosest
pointofapproach(CPA)inthehorizontaldimension– Modifiedtau():ProjectedtimetoCPA
• DistanceModification(DMOD):Minimumthreatrangeboundary
• VerticalComponents:– dh:Currentverticalseparation– ZTHR:ProjectedverticalseparationatCPA– Verticaltau():Projectedtimetoco-altitude
7
vt
modt
LossofDAAWellClear
• LossofDAAwellclear:
• UASExecutiveCommitteeScienceandResearchPanelcoordinatedresearcheffortsby:– NASA– MassachusettsInstituteofTechnology-LincolnLaboratory,and– UnitedStatesAirForceResearchLaboratory
• FeedbackfromtheFAAandRTCASC-228incorporated
8
mod0 35sec AND 4000ft AND 450fthHMD dt£ < < <
dh
UAS
DAAWarningalert
• DAAWarningalert(look-aheadtimeof40sec):
• AlerttotheUASpilottoexecuteamaneuvertoremainwellclear
9
mod0 35sec AND 0.75nmi AND 450fthHMD dt£ < < <
dh
UAS
DAA alert issued
timeCA region
crossedTCAS RA
issued
“AND”CollisionAvoidanceRegionDefinition
• “AND”definitioninthepreliminarystandards(mid-2015):
• UtilizessubsetofthecomponentsusedinTCAS
10
mod0 50sec AND (0 50sec AND 800ft)v ZTHRt t£ < £ < <
UASx xx x
xxx
vt
DAA alert issued
timeCA region
crossedTCAS RA
issued
ZTHRof0ftinthisexample
“OR”CollisionAvoidanceRegionDefinition
• “OR”definition:
• MoresimilartoTCASlogic
11
DAA alert issued
timeCA region
crossedTCAS RA
issued
mod0 50sec AND (0 50sec OR 800ft)v ZTHRt t£ < £ < <
“OR-h”CollisionAvoidanceRegionDefinition
• “OR-h”definition:
• UtilizescurrentverticalseparationlikeTCASandDAAalerting
12
DAA alert issued
timeCA region
crossedTCAS RA
issued
mod0 50sec AND (0 50sec OR 800ft)v hdt t£ < £ < <
SummaryofCARegionDefinitions
• “AND”definitioninthepreliminarystandardsdocument:
• “OR”definitionmoresimilartoTCAS:
• “OR-h”definitionutilizescurrentverticalseparationlikeTCASandDAAalerting
13
mod0 50sec AND (0 50sec AND 800ft)v ZTHRt t£ < £ < <
mod0 50sec AND (0 50sec OR 800ft)v ZTHRt t£ < £ < <
mod0 50sec AND (0 50sec OR 800ft)v hdt t£ < £ < <
DataCollection
14
Approach
• 1.3millionsimulatedpairwiseencountersbetweenUASandmannedaircraft– NASA’sJavaArchitectureforDAAExtensibilityandModeling
(Abramson,NASA-TM-2017-219507)
• Combinatorialapproach– Coversawiderangeofhorizontalandverticalclosurerates,angles,
andmissdistances– Capture“cornercases”unlikelytooccurinnationwidesimulations
15
EncounterDetails
16
• Straight-line,non-maneuveringpairwiseencounters• Simplekinematictrajectorymodeler• Nouncertainty• TCASIIversion7.1
• RecordedwhenTCASRAs,CAregioncrossings,andDAAWarningalertsoccur(ifever)foranalysis
340kencounters
800k-1.1Mencounters
VerticalEncounterTypes
17
Level-Level
Encounters
Level-Descent
Encounters
Level-Climb
Encounters
UAS
UAS
UAS
HorizontalEncounterTypes
18
UAS
Head-On Encounters
Crossing Encounters
UAS
Overtaking Encounters
UAS
EncounterswithNon-ZeroMissDistances
Mannedaircrafttrajectoryisoffsethorizontally
andalsooffsetvertically
toevaluateperformanceofCAregiondefinitionsinencounterswithnon-zeromissdistances
UAS
UAS
19
EncounterParameters
20
1.3millionpairwiseencountersbetweenUASandmannedaircraftParameter Type # Values ValuesUASgroundspeed 4 50, 100,150,200kts
UAS heading 1 0deg
UASverticalspeed 1 0ft/min (flylevelat5000ft)
Mannedverticalspeed 9 -2000,-1500,-1000,-500,0,…,2000ft/min
Mannedheading 12 0,30,60,90,120,150,180,…, 330deg
Mannedgroundspeed 5 50,100,150,200,250kts
Horizontalmannedtrajectory offset
9 0nmi:(x,y)=(0,0)0.5nmi:(x,y)=(0.5,0),(-0.5,0),(0,0.5),(0,-0.5)1.5nmi:(x,y)=(1.5,0),(-1.5,0),(0,1.5),(0,-1.5)
Verticalmannedtrajectoryoffset
7 -1000, -500,-250,0,250,500,1000ft
UAStrial planmaneuverturnrate
2 1.5,3deg/sec
UAStrialplanclimb/descent rate
5 (500,500),(1000,1000),(2000,2000),(2000,1000),(1000,2000)ft/min
Result1:“AND”CollisionAvoidanceRegionDefinitionNotSuitable
21
“AND”CARegionDefinitionNotSuitable
The“AND”definitiondoesnotensurethattheCAregionisalwayscrossedbeforeaTCASRAisissued
TCASRA CAregioncrossed
22
Using“OR”and“OR-h”definitionsresultedinnoundesirablecasesinwhichTCASRAoccursbeforeCA
regioniscrossed
“OR”“AND"
%encounterswithTCASRA
“OR-h”
6.2%
0
5
10
15
20
Evenonecaseisunacceptable
SlowVerticalClosureRatewhenTCASRAwasissuedbeforethe“AND”CAregionwascrossed
23
“AND”definitiondoesnotcaptureslowverticalclosureratecases--> Needtouse“OR”likeinTCAS
“AND”
Vertical separation: 592 ftVertical closure rate: 500 ft/min (i.e., converging)Vertical tau: 71.0 sec
Horizontal separation: 0 nmiHorizontal closure rate: 0 ktsHorizontal encounter angle: 0 degModified tau: 0 sec
UASMannedaircraftTCASissuesRAbecausecurrentverticalseparationislessthan600ftBut,“AND”CAregionnot
crossedduetoslowverticalclosurerate
mod0 50sec AND (0 50sec AND 800ft)v ZTHRt t£ < £ < <
“AND”CARegionDefinitionNotSuitable
The“AND”definitiondoesnotensurethattheCAregionisalwayscrossedbeforeaTCASRAisissued
24
TCASRAEvenonecaseisunacceptable
Using“OR”and“OR-h”definitionsresultedinnoundesirablecasesinwhichTCASRAoccursbeforeCA
regioniscrossed
“OR”“AND"
%encounterswithTCASRA
“OR-h”0
5
10
15
2016.5%
Level-LevelEncounterwhenTCASRAwasissuedwithoutthe“AND”CAregioneverbeingcrossed
25
MannedaircraftTCASissuesRAbecausecurrentverticalseparationislessthan600ftBut,“AND”CAregionnotcrossedbecauseaircraftinlevel-levelencounterwithoffsetareneverco-altitude
Vertical separation: 500 ftVertical closure rate: 0 ft/minHorizontal separation: 1.17 nmiHorizontal closure rate: 200 kts (i.e., converging)Horizontal encounter angle: 180 deg (i.e., head-on)Modified tau (DMOD 1.1 nmi): 2.4 sec
UAS
500 ft
“AND”definitiondoesnotcapturezeroverticalclosureratecases-->Needtouse“OR”likeinTCAS
“AND” mod0 50sec AND (0 50sec AND 800ft)v ZTHRt t£ < £ < <
Result2:“OR-h”CollisionAvoidanceRegionDefinitionhasLowerNon-InteroperabilitywithDAAWarningAlerts
26
“OR-h”CARegionDefinitionhasLowerNon-Interoperability
The“OR-h”definitionrestrictedverticalguidanceatDAAWarningalertslessoften
CAregion DAAWarning
27
Fewestispreferable
“OR”
%encounterswithCAregioncrossing
“OR-h”0
10
20
30
40
23.8%
3.2%
HighVerticalClosureRatewhen“OR”CAregionwascrossedbeforeDAAWarningalertwasissued
28
mod0 50sec AND (0 50sec OR 800ft)v ZTHRt t£ < £ < <“OR”
“OR”definitionistooconservativeinhighverticalclosureratecasesduetoZTHR-->UsecurrentverticalseparationlikeinDAAWarningalert
Vertical separation: 2033 ftVertical closure rate: 2000 ft/min (i.e., converging)Vertical tau: 61 secPredicted vertical separation at CPA: 0 ft
Horizontal separation: 2.54 nmiHorizontal closure rate: 150 kts (i.e., converging)Horizontal encounter angle: 180 degModified tau (DMOD 1.1 nmi): 49.5 sec
UAS
“OR”CAregioniscrossedbecausethetwoaircraftarepredictedtohave0ftofverticalseparationatCPA
But,thereisnoDAAalertor“OR-h”CAregioncrossingsinceverticalseparationatthistimeismorethan800ft
29
ConcludingRemarks
RecommendationtoRTCASC-228
RecommendedchangingCAregionfromthe“AND”definitioninthepreliminarystandardsdocumenttothe“OR-h”definitioninthefinalstandardsdocument:
• “OR-h”ismostinteroperablewithTCASandDAAWarningalertsbecauseituses:– “OR”operatorinsteadof“AND”operatorfortheverticalconditions– Currentverticalseparationinsteadofpredictedverticalseparation
atCPA• “OR-h”definitionwasacceptedbyRTCASC-228forthefinal
standardsdocumentforUASDAAsystems
30
mod0 50sec AND (0 50sec OR 800ft)v hdt t£ < £ < <
FutureDirections
• EncountersinwhichUASclimbanddescend• EncountersinwhichUASandmannedaircraftmaneuver
• Uncertainty:– Sensormodels– Trackermodels– Pilotmodels
• ACASXa(active)formannedaircraft• ACASXu(unmanned)forUAS
31
RecommendationtoRTCASC-228
RecommendedchangingCAregionfromthe“AND”definitioninthepreliminarystandardsdocumenttothe“OR-h”definitioninthefinalstandardsdocument:
• “OR-h”ismostinteroperablewithTCASandDAAWarningalertsbecauseituses:– “OR”operatorinsteadof“AND”operatorfortheverticalconditions– Currentverticalseparationinsteadofpredictedverticalseparation
atCPA• “OR-h”definitionwasacceptedbyRTCASC-228forthefinal
standardsdocumentforUASDAAsystems
Questions?Email:[email protected] 32
mod0 50sec AND (0 50sec OR 800ft)v hdt t£ < £ < <
