Fatigue-is-a-risk-factor-for-flight-performance.docx

Fatigueisariskfactorforflightperformanceandsafetyincommercialaviation.InUScommercialavi-ation,tohelptocurbfatigue,themaximumdurationofflightdutyperiodsisregulatedbasedonthescheduledstarttimeandthenumberofflightsegmentstobeflown.Thereisscientificsupportforregu-latingmaximumdutydurationbasedonscheduledstarttime;fatigueiswellestablishedtobemodulatedbycircadianrhythms.However,ithasnotbeenestablishedscientificallywhetherthenumberofflightsegments,perse,affectsfatigue.Toaddressthissciencegap.weconductedarandomized,counterbalanced,cross-overstudywith24active-dutyregionalairlinepilots.Objectiveandsubjectivefatiguewascomparedbetweena9-hordutydaywithmultipletake-offsandlandingsversusadutydayofequaldurationwithasingletake-offandlanding.Tostandardizeexperimentalconditionsandisolatethefatiguingeffectofthenumberofsegmentsflown,theentiredutyscheduleswerecarriedoutinahigh-fidelity,moving-base,full-flight,regionaljetflightsimulator.Stepsweretakentomaintainoperationalrealism,includingsimulatedair-planeinspectionsandacceptancechecks,useofrealisticdispatchreleasesandairportcharts,real-worldairtrafficcontrolinteractions,etc.Duringeachofthetwodutydays,10fatiguetestboutswereadmiis-tered,whichincludeda10-minutePsychomotorVigilanceTest(PVT)assessmentofobjectivefatigueandSamn-Perelli(SP)andKarolinskaSleepinessScale(KSS)assessmentsofsubjectivesleepiness-fatigue.Resultsshowedagreaterbuild-upofobjectiveandsubjectivefatigueinthemulti-segmentdutydaythaninthesingle-segmentdutyday.Withdutystarttimeanddurationandothervariablesthatcouldimpactfatiguelevelsheld11stant.thegreaterbuild-upoffatigueinthemulti-segmentdutydaywasattributablespecificallytothedifferenceinthenumberofflightsegmentsflown.Comparedtofindingsinpreviouslypublishedlaboratorystudiesofsimulatednightshiftsandnighttimesleepdeprivation,themagnitudeofthefatiguingeffectofthemultipletake-offsandlandingswasmodest.Ratingsofflightperformancewerenotsignificantlyreducedforthesimulatedmulti-segmentdutyday.TheUSdutyandflighttimeregulationsforcommercialaviationshortenthemaximumdutydurationinmulti-segmentoperationsbyupto25%dependingfunctionoftimeawake(Daanetal.,1984;Dijketal.,1992).Thecircadianandhomeostaticprocessesinteracttogeneratepredictabledielpat-ternsoffatigue(DijkandCzeisler,1994;GabehartandVanDongen,inpress),wherethetermfatiguereferstosleepinessandperfor-manceimpairment(asiscommonpracticeinoperationalsettings;seeSatterfieldandVanDongen,2013).Inthiscontext,regulatingmaximumdutydurationsasafunctionofstarttimetohelpmitigatefatigueandimprovesafetymakessense(VanDongenandHursh12010),especiallyindaytime-orientedoperations(additionalcom-plexitieslimittheeffectivenessofsuchregulationsinnighttimeoperations;e.g.,seeRanganetal.,2013).Thefatiguesciencepertainingtonumberofsegmentsflownisnotaswelldeveloped.Mostoftheliteratureonaviationandfatiguehasfocusedonlong-rangeandultra-long-rangeflights(Holmesetal.,2012;Ganderetal.,2014)ratherthanshort-range,multi-segmentoperations.1.imitedevidencepertainingtoshort-rangeflightoperationscomesfromfieldstudies,inwhichpilots'sub-jectiveratingsoffatiguewerefoundtoincreasewiththenumberofsegmentsflowninthedutyperiod(Powelletal.,2007,2008).Inthesestudies,dutyschedulesandoperationalconditionswerenotstandardized,leavingtoomanypotentialconfoundstobeabletodrawconclusionsregardingthefatiguingeffectofflyingmul-tiplesegmentsperse.Noobjectivedatapertainingtofatigueinmulti-segment,short-rangeoperationshavebeenpublished.Still,itstandstoreasonthattheremaybeafatiguingeffectofflyingmultiplesegmentsinadutyday-inparticular,afatiguingeffectofmultipletake-offsandlandings.Thesecriticalphasesofflightarearguablythemostsafety-sensitive,andtheytypicallyhavethehighesttaskload(Hoermannetal.,2015).Asystemsbiologyviewofthebrainmechanismsunderlyingcognitiveimpairmentduetofatigue(VanDongenetal.,2011a)positsthattheeffectoffatigueonalertnessandperformanceiseuroalcircuituse-dependent,andisthuspredictedtobeafunc-tionoftaskload.Thispredictionhasbeenconfirmedinlaboratorystudies,whichhaveshownthatincreasedtaskloadacceleratesthedegradationofsubjectivealertnessandcognitiveperformanceduetocircadianrhythmandsleeploss(VanDongenandDinges,2007;Goeletal.,2014).Yet,theeffectofincreasedtaskloadonalertnessandperformanceinthelaboratoryappearstobemodestinmag-nitde.anditisaprioriuncleartowhatextentittranslatestoasignificanteffectofmultipletake-offsandlandingsinreal-worldoperations.Theobjectiveofthepresentstudywastohelpfillthissciencegap.Inactive-dutyregionalairlinepilots,wecomparedtheeffectoffatigueonalertnessandperformancebetweenadutyschedulecontainingmultiplesegmentsandadutyschedulentainingonlyasinglesegment.Dutystarttimeanddurationwereheldconstant,andtheorderofconditionswasrandomizedandcounterbalanced,withpilotsservingastheirowncontrols.Thedutyperiodswerecarriedoutusingahigh-fidelity,moving-base,full-flightsimla-tor.Thisenabledustostandardizeandaccountforotherfatiguefactorscommonlyencounteredinreal-worldcommercialaviation(e.g.,airtrafficdensity,weather,scheduledelays),whileretainingahighdegreeo