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1stEdition:2011
Fatigue Risk Management
Systems (FRMS)
Implementation Guide
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NOTE
DISCLAIMER. The information contained in this publication is subject to constant review in the light
of changing government requirements and regulations. No subscriber or other reader should act on the
basis of any such information without referring to applicable laws and regulations and without taking
appropriate professional advice. Although every effort has been made to ensure accuracy, the
International Air Transport Association (IATA), and the International Civil Aviation Organization
(ICAO) shall not be held responsible for any loss or damage caused by errors, omissions, misprints or
misinterpretation of the contents hereof. Furthermore, the International Air Transport Association and
the International Civil Aviation Organization expressly disclaim any and all liability to any person or
entity, whether a purchaser of this publication or not, in respect of anything done or omitted, and the
consequences of anything done or omitted, by any such person or entity in reliance on the contents of
this publication.
Opinions expressed in this publication do not necessarily reflect the opinion of the International AirTransport Association. The mention of specific companies, products in this publication does not imply
that they are endorsed or recommended by the International Air Transport Association in preference
to others of a similar nature which are not mentioned.
International Air Transport Association 2011. All Rights Reserved. No part of this publication may be
reproduced, recast, reformatted or transmitted in any form by any means, electronic or mechanical,
including photocopying, recording or any information storage and retrieval system, without the prior
written permission from:
Senior Vice President
Safety, Operations and Infrastructure
International Air Transport Association
800 Place Victoria, P.O. Box 113
Montral, Qubec
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IATA/ICAOFRMSImplementationGuideforOperators
NOTE:
ThisguideisajointdocumentcreatedthroughICAO/IATA collaboration
ThisdocumenthasbeenapprovedbyIATAbutisyettobeapprovedbyICAOCouncilandisthereforesubject
tochange.
Thisdocumentisstillindraftform(preproduction)~somefootnotes,numberingmaybeincorrect
Thisdocumentcontainscontentonly:prefaceandendorsementsarenotyetincluded
Thisdocument,oncecomplete,willbeavailableonlinefreeofcharge
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ContentsIATAFRMSImplementationGuide...........................................................................................................................1
ChapterOne:IntroductiontoFatigueRiskManagementSystems(FRMS) .............................................................7
1.1 WhatisaFatigueRiskManagementSystem?..........................................................................................7
1.2WhytheAviationIndustryisIntroducingFRMS.............................................................................................8
1.3 ICAORequirementsforFatigueRiskManagementSystems....................................................................9
1.4StructureofthisManual...............................................................................................................................12
ChapterTwo:ScienceforFRMS .............................................................................................................................15
2.1IntroductiontoScienceforFRMS.................................................................................................................15
2.2EssentialSleepScience.................................................................................................................................15
2.2.1WhatisHappeningintheBrainDuringSleep .......................................................................................15
2.2.2
The
Issue
of
Sleep
Quality .....................................................................................................................19
2.2.3ConsequencesofNotGettingEnoughSleep.........................................................................................21
2.3IntroductiontoCircadianRhythms ..............................................................................................................24
2.3.1ExamplesofCircadianRhythm..............................................................................................................24
2.3.2TheCircadianBodyClockandSleep......................................................................................................26
2.3.3SensitivityoftheCircadianBodyClocktoLight ....................................................................................28
2.3.4ShiftWork..............................................................................................................................................29
2.3.5JetLag ....................................................................................................................................................31
2.4SummaryofEssentialScienceforFRMS ......................................................................................................35
ChapterThree:FRMSPolicyandDocumentation..................................................................................................46
3.1IntroductiontoFRMSPolicyandDocumentation........................................................................................46
3.2FRMSPolicy ..................................................................................................................................................47
3.2.1ScopeoftheFRMS.................................................................................................................................47
3.3.2ThingsthattheFRMSPolicyMustCover ..............................................................................................48
3.3ExamplesofFRMSPolicyStatements ..........................................................................................................49
3.3.1FRMS
Policy
Statement
for
aMajor
Air
Carrier.....................................................................................50
3.3.2FRMSPolicyStatementforaSmallerOperatorProvidingMedicalEvacuationServices......................51
3.4 FRMSDocumentation.............................................................................................................................52
3.4.1ExampleofTermsofReferenceforaFatigueSafetyActionGroup......................................................53
ChapterFour:FatigueRiskManagement(FRM)Processes ...................................................................................55
4.1IntroductiontoFRMProcesses ....................................................................................................................55
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4.2FRMProcessesStep1:IdentifytheOperationsCovered.............................................................................59
4.3FRMProcessesStep2:GatherInformationandAdditionalDataifNeeded................................................59
4.4FRMProcessesStep3:HazardIdentification...............................................................................................62
4.4.1PredictiveHazardIdentificationProcesses ...........................................................................................62
4.4.2ProactiveHazardIdentificationProcesses ............................................................................................65
4.4.3ReactiveHazardIdentificationProcesses..............................................................................................71
4.5FRMProcessesStep4:RiskAssessment ......................................................................................................72
4.6FRMProcessesStep5:RiskMitigation.........................................................................................................74
4.7Example:SettingupFRMProcessesforANewULRRoute..........................................................................78
4.7.1:Step1IdentifytheOperation............................................................................................................78
4.7.2:Step2GatherandAnalyzeAvailableInformation ............................................................................78
4.7.3:Step3IdentifyHazards......................................................................................................................81
4.7.4:Step4AssessSafetyRisk ...................................................................................................................82
4.7.5:Step5SelectandImplementControlsandMitigations....................................................................82
4.7.5:Step6MonitorEffectivenessofControlsandMitigations ...............................................................83
4.7.6:LinkingtoFRMSSafetyAssuranceProcesses.......................................................................................83
ChapterFive:FRMSSafetyAssuranceProcesses ...................................................................................................85
5.1IntroductiontoFRMSSafetyAssuranceProcesses ......................................................................................85
5.2FRMSSafetyAssuranceProcessesStep1:CollectandReviewData ...........................................................89
5.3FRMSSafetyAssuranceProcessesStep2:EvaluateFRMSPerformance.....................................................91
5.4FRMSSafetyAssuranceProcessesStep3:IdentifyEmergingHazards ........................................................92
5.5FRMSSafetyAssuranceProcessesStep4:IdentifyChangesAffectingFRMS..............................................93
5.6FRMSSafetyAssuranceProcessesStep5:ImproveEffectivenessofFRMS ................................................94
5.7AssigningResponsibilityforFRMSSafetyAssuranceProcesses ..................................................................94
5.8ExamplesofFRMSSafetyAssuranceProcessesInteractingWithFRMProcesses.......................................95
ChapterSix:FRMSPromotionProcesses .............................................................................................................104
6.1 IntroductiontoFRMSPromotionProcesses ........................................................................................104
6.2 FRMSTrainingPrograms ......................................................................................................................106
6.2.1 WhoNeedstobeTrained.............................................................................................................106
6.2.2 Curriculum ....................................................................................................................................106
6.2.3FRMSTrainingFormatsandFrequency...............................................................................................110
6.2.3 FRMSTrainingEvaluation.............................................................................................................110
6.2.5 FRMSTrainingDocumentation.....................................................................................................111
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6.3 FRMSCommunicationsPlan.................................................................................................................111
ChapterSeven:FRMSImplementation ................................................................................................................1 13
7.1 IntroductiontoFRMSImplementation ................................................................................................113
7.2 PhaseI:Planning...................................................................................................................................114
7.3 PhaseII:ImplementReactiveFRMProcesses......................................................................................115
7.4 PhaseIII:ImplementProactiveandPredictiveFRMProcesses ...........................................................115
7.5 PhaseIV:ImplementFRMSSafetyAssuranceProcesses .....................................................................116
7.6 OperationalExampleofStagedFRMSImplementation.......................................................................116
AppendixA:Glossary............................................................................................................................................119
AppendixB:MeasuringCrewmemberFatigue ....................................................................................................124
B1 CrewmembersRecallofFatigue..........................................................................................................125
B1.1 FatigueReportingForms ..................................................................................................................125
B1.2 RetrospectiveSurveys ......................................................................................................................127
B2 MonitoringCrewmemberFatigueDuringFlightOperations ...............................................................128
B2.1 SubjectiveFatigueandSleepinessRatings.......................................................................................128
B2.2 ObjectivePerformanceMeasurement.............................................................................................132
B2.3 MonitoringSleep ..............................................................................................................................133
B2.4 MonitoringtheCircadianBodyClockCycle .....................................................................................140
B3 EvaluatingtheContributionofFatiguetoSafetyEvents .....................................................................142
AppendixC:ProceduresforControlledRestontheFlightDeck..........................................................................148
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ChapterOne:IntroductiontoFatigueRiskManagementSystems(FRMS)
The
purpose
of
this
FRMS
Implementation
Guide
is
to
provide
air
operators
with
information
for
implementing
anFRMSthatisconsistentwithICAOStandardsandRecommendedPractices(SARPs).AstheICAOprovisionsforFRMSevolve,everyeffortwillbemadetokeepthismanualuptodate.However,itisrecommendedthatoperators check the current SARPs to find out if anything important has changed since this version of themanualwasdeveloped.OperatorsalsoneedtoensurethattheirFRMSmeetstherequirementsoftheirStatesregulatoryauthority.
AvarietyofoptionstoaddresstheICAOStandardsforanFRMSarepresentedthroughoutthisguide.Thesecanbeadaptedtotheneedsofdifferentsizesandtypesofoperators (international,domestic,passenger,cargo,etc)andtospecificoperations(UltraLongRange(ULR),longhaul,shorthauldomestic,oncall/charter,etc). Itis not necessary to implement all of these options to have an effective FRMS that meets regulatoryrequirements.
1.1WhatisaFatigueRiskManagementSystem?Crewmemberfatiguecanbedefinedas:
Aphysiological state of reducedmental orphysicalperformance capability resultingfrom sleep loss or
extendedwakefulness, circadianphase, orworkload (mental and/orphysical activity) that can impair a
crewmembersalertnessandabilitytosafelyoperateanaircraftorperformsafetyrelatedduties.
Fatigueisamajorhumanfactorshazardbecauseitaffectsmostaspectsofacrewmembersabilitytodotheirjob.ICAOdefinesaFatigueRiskManagementSystem(FRMS)as:
Adatadrivenmeansof continuouslymonitoringandmanagingfatiguerelated safety risks,basedupon
scientific principles and knowledge as well as operational experience that aims to ensure relevant
personnelareperformingatadequatelevelsofalertness.
AnFRMSaims to ensure that flight andcabincrew members aresufficientlyalertso theycan operate toasatisfactorylevelofperformance. ItappliesprinciplesandprocessesfromSafetyManagementSystems(SMS)1tomanagethespecificrisksassociatedwithcrewmemberfatigue. LikeSMS,FRMSseekstoachievearealisticbalance between safety, productivity, and costs. It seeks to proactively identify opportunities to improveoperationalprocessesandreducerisk,aswellasidentifyingdeficienciesafteradverseevents.ThestructureofanFRMSasdescribedhereismodelledontheSMSframework.Thecoreactivitiesaresafetyriskmanagement(described in the SARPS as FRM processes) and safety assurance (described in the SARPs as FRMS safetyassuranceprocesses).ThesecoreactivitiesaregovernedbyanFRMSpolicyandsupportedbyFRMSpromotionprocesses,andthesystemmustbedocumented.
BothSMSandFRMSrelyontheconceptofaneffectivesafetyreportingculture1,wherepersonnelhavebeentrainedandareconstantlyencouragedtoreporthazardswheneverobservedintheoperatingenvironment.To
1 SeeICAOSafetyManagementManual(Doc9859)andIATAIntroductiontoSafetyManagementSystems(SMS),2nd
Edition.
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encourage the reporting of fatigue hazards by all personnel involved in an FRMS, an operator must clearlydistinguishbetween:
unintentionalhumanerrors,whichareacceptedasanormalpartofhumanbehaviorandarerecognizedandmanagedwithintheFRMS;and
deliberateviolationsofrulesandestablishedprocedures.AnoperatorshouldhaveprocessesindependentoftheFRMStodealwithintentionalnoncompliance.
Toencourageanongoingcommitmentbypersonneltoreportingfatiguehazards,theorganizationmusttakeappropriate action in response to those reports. When an effective safety reporting system exists, a largepercentageofsafetyreportsfromoperationalpersonnelrelateto identifiedorperceivedhazards, insteadoferrorsoradverseevents.
1.2WhytheAviationIndustryisIntroducingFRMSThe traditional regulatory approach to managing crewmember fatigue has been to prescribe limits onmaximumdaily,monthly,andyearlyflightanddutyhours,andrequireminimumbreakswithinandbetween
dutyperiods.Thisapproachcomesfromalonghistoryoflimitsonworkinghoursdatingbacktotheindustrialrevolution.Itenteredthetransportationsectorintheearly20thcenturyinaseriesofregulationsthatlimitedworking hours in rail, road and aviation operations2. The approach reflects early understanding that longunbrokenperiodsofworkcouldproducefatigue(nowknownastimeontaskfatigue),andthatsufficienttimeisneededtorecoverfromworkdemandsandtoattendtononworkaspectsoflife.
Inthesecondhalfofthe20thcentury,scientificevidencebeganaccumulatingthatimplicatedothercausesoffatigue in addition to timeontask, particularly in 24/7 operations. The most significant new understandingconcerns:
thevital importanceofadequatesleep (notjustrest)forrestoringandmaintainingallaspectsofwaking
function;and
dailyrhythmsintheabilitytoperformmentalandphysicalwork,andinsleeppropensity(theabilitytofallasleepandstayasleep),thataredrivenbythedailycycleofthecircadianbiologicalclockinthebrain.
This new knowledge is particularly relevant in the aviation industry which is unique in combining 24/7operationswithtransmeridianflight.
Inparallel,understandingofhumanerroranditsroleinaccidentcausationhasincreased.Typically,accidentsand incidents result from interactionsbetweenorganizationalprocesses (i.e. workplaceconditions that leadcrewmemberstocommitactivefailures),andlatentconditionsthatcanpenetratecurrentdefensesandhaveadverseeffectsonsafety1.TheFRMSapproachisdesignedtoapplythisnewknowledgefromfatiguescienceand safetyscience. It is intended to providean equivalent, or enhanced, level of safety, while alsoofferinggreateroperationalflexibility.
Prescriptiveflightanddutytimelimitsrepresentasomewhatsimplisticviewofsafetybeinginsidethelimitsissafewhilebeingoutsidethelimitsisunsafeandtheyrepresentasingledefensivestrategy.Whiletheyare
2GanderPH,HartleyL,PowellD,CabonP,HitchcockE,MillsA.PopkinS(2010).FatigueriskmanagementI:organizational
factors.AccidentAnalysisandPrevention(inpress).
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Prescriptiveflightand
dutytimelimitations
Addressestransientandcumulativefatigue Sharedoperatorindividualresponsibility
SMS
Effectivesafetyreporting Seniormanagementcommitment Continuousmonitoringprocess Investigationofsafetyoccurrences Sharingofinformation Integratedtraining EffectiveimplementationofSOPs Continuousimprovement
However,anFRMS,asamanagementsystem focusedon fatigue,alsohasadded requirementsbeyond thatwhich would be expected of an operator complying with prescriptive flight and duty time limitations andmanaging their fatiguerisks through theirSMS. InmeetingtheseadditionalFRMSspecificrequirements,anoperatorwithanapprovedFRMSmaymoveoutsidetheprescribedlimits. Therefore,thefatiguemanagementSARPs in Section 4.10, Annex 6, Part I, include particular Standards that enable the effective regulation ofFRMS.
The following text box contains the SARPs in Annex 6 Part I that relate to Fatigue Management. States arerequiredtohaveregulationsforprescriptiveflightanddutytimelimitations,buttheyalsohavetheoptiontoestablishFRMSregulations. Inaddition,there isarequirementthatwhenFRMS isused,operationsmanualsreflecttheFRMSoption(Annex6,PartI,Appendix2).
Appendix8hasbeenaddedtoAnnex6,PartItogivedetailedrequirementsforanFRMSwhichmustinclude,ataminimum,thefollowingcomponents.
1. FRMSpolicyanddocumentation;2. Fatigueriskmanagementprocesses;3. FRMSsafetyassuranceprocesses;and4. FRMSpromotionprocesses.
Table1.1showshowthesecomponentsmaptotherequirementsofSMS. Annex6,PartI,recommendsthat,whereanoperatorhasanFRMS,itisintegratedwiththeoperatorsSMS.
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Annex6PartI
4.10FatigueManagement
4.10.1 TheStateoftheOperatorshallestablishregulationsforthepurposeofmanagingfatigue.Theseregulationsshallbebaseduponscientificprinciplesandknowledge,withtheaimofensuringthatflightandcabincrewmembersareperformingatanadequatelevelofalertness.Accordingly,theStateoftheOperatorshallestablish:
a) regulationsforflighttime,flightdutyperiod,dutyperiodandrestperiodlimitations;andb) whereauthorizinganoperatortouseaFatigueRiskManagementSystem(FRMS)tomanagefatigue,FRMS
regulations.
4.10.2 TheStateoftheOperatorshallrequirethattheoperator,incompliancewith4.10.1andforthepurposesofmanagingitsfatiguerelatedsafetyrisks,establisheither:
a) flighttime,flightdutyperiod,dutyperiodandrestperiodlimitationthatarewithintheprescriptivefatiguemanagementregulationsestablishedbytheStateoftheOperator;or
b) aFatigueRiskManagementSystem(FRMS)incompliancewith4.10.6foralloperations;orc) anFRMSincompliancewith4.10.6forpartofitsoperationsandtherequirementsof4.10.2a)fortheremainderof
itsoperations.
4.10.3 Wheretheoperatoradoptsprescriptivefatiguemanagementregulationsforpartorallofitsoperations,theStateoftheOperatormayapprove,inexceptionalcircumstances,variationstotheseregulationsonthebasisofariskassessmentprovidedbytheoperator.Approvedvariationsshallprovidealevelofsafetyequivalentto,orbetterthan,thatachievedthroughtheprescriptivefatiguemanagementregulations.
4.10.4 TheStateoftheOperatorshallapproveanoperatorsFRMSbeforeitmaytaketheplaceofanyoralloftheprescriptivefatiguemanagementregulations.AnapprovedFRMSshallprovidealevelofsafetyequivalentto,orbetterthan,theprescriptivefatiguemanagementregulations.
4.10.5 StatesthatapproveanoperatorsFRMSshallestablishaprocesstoensurethatanFRMSprovidesalevelofsafetyequivalentto,orbetterthan,theprescriptivefatiguemanagementregulations.Aspartofthisprocess,theStateoftheOperatorshall:
a) requirethattheoperatorestablishmaximumvaluesforflighttimesand/orflightdutyperiods(s)andduty
period(s),andminimumvaluesforrestperiods.Thesevaluesshallbebaseduponscientificprinciplesandknowledge,subjecttosafetyassuranceprocesses,andacceptabletotheStateoftheOperator;
b)mandateadecreaseinmaximumvaluesandanincreaseinminimumvaluesintheeventthattheoperatorsdataindicatesthesevaluesaretoohighortoolow,respectively;and
c) approveanyincreaseinmaximumvaluesordecreaseinminimumvaluesonlyafterevaluatingtheoperatorsjustificationforsuchchanges,basedonaccumulatedFRMSexperienceandfatiguerelateddata.
4.10.6 WhereanoperatorimplementsanFRMStomanagefatiguerelatedsafetyrisks,theoperatorshall,asaminimum:a) incorporatescientificprinciplesandknowledgewithintheFRMS;b) identifyfatiguerelatedsafetyhazardsandtheresultingrisksonanongoingbasis;c) ensurethatremedialactions,necessarytoeffectivelymitigatetherisksassociatedwiththehazards,are
implementedpromptly;d) provideforcontinuousmonitoringandregularassessmentofthemitigationoffatiguerisksachievedbysuch
actions;ande) provideforcontinuousimprovementtotheoverallperformanceoftheFRMS.
4.10.7 Recommendation.Statesshouldrequirethat,whereanoperatorhasanFRMS,itisintegratedwiththeoperatorsSMS.
4.10.8 Anoperatorshallmaintainrecordsforallitsflightandcabincrewmembersofflighttime,flightdutyperiods,dutyperiods,andrestperiodsforaperiodoftimespecifiedbytheStateoftheOperator.
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Table1.1ComparingSMSandFRMSComponents
SMSFramework FRMS
1. Safetypolicyandobjectives 1. FRMSpolicyanddocumentation
2. Safetyriskmanagement 2. FRMprocesses Identificationofhazards Riskassessment Riskmitigation
3. Safetyassurance 3. FRMSsafetyassuranceprocesses FRMSperformancemonitoring Managementofoperationalandorganisational
change ContinuousFRMSimprovement
4. Safetypromotion 4. FRMSpromotionprocesses Trainingprograms FRMScommunicationplan
ThecoreoperationalactivitiesoftheFRMSaretheFRMprocessesandtheFRMSsafetyassuranceprocesses.TheyaresupportedbyorganizationalarrangementsdefinedintheFRMSpolicyanddocumentation,andbytheFRMSpromotionprocesses.
1.4StructureofthisManualFigure 1.1 shows a basic framework linking the required components of an FRMS. For ease of explanation,Figure 1.1 presents a single, central, functional group, designated as the Fatigue Safety Action Group,
responsibleforalloftheseFRMScomponents. TheFatigueSafetyActionGroupincludesrepresentativesofallstakeholdergroups (management,scheduling,andcrewmembers)andother individualsasneededtoensurethat ithasappropriateaccesstoscientificandmedicalexpertise. However,dependingontheorganizationalstructure,someoftheFatigueSafetyActionGroupfunctionsasdescribedinthismanualmaybeundertakenbyothergroupswithintheorganization(discussedfurtherinChapter3). Theimportantthingisthat,irrespectiveofwhodoesthem,allofthecomponentfunctionsrequiredunderanFRMSbeperformed.
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Figure1.1:LinkingtherequiredcomponentsofanFRMS
The Fatigue Safety Action Group coordinates the FRM processes (the daytoday fatigue risk managementactivities). The FRMS safety assurance processes monitor how well the FRMS is functioning from a systemperspective.TheyalsoprovideinputforadaptingtheFRMStomeetchangingoperationaldemandsandforitscontinuousimprovement.
Communicationbetween theFRMSprocessesand theSMS (inbothdirections) isnecessary to integrate themanagementofthefatiguerisksintothebroaderriskmanagementactivitiesoftheSMS.
The detailed structure of an FRMS, and the specific ways in which it links to an operators SMS, will varyaccordingto:
thesizeoftheorganization; thetypeandcomplexityoftheoperationsbeingmanaged; therelativematurityoftheFRMSandtheSMS;and therelativeimportanceofthefatiguehazards.
TheFRMS
approach
isbased
onapplying
scientific
principles
and
knowledge
to
manage
crewmember
fatigue.
ChapterTwointroducestheessentialscientificconceptsthatareneededtodevelopandimplementanFRMS.
ChaptersThree,Four,Five,andSixeachdealwithoneoftherequiredFRMScomponents.ChapterSevensteps
thoughastagedapproachforimplementinganFRMS.
AppendicesA,BandCprovideextrainformationtosupportthatprovidedintheprecedingchapters. Forease
ofreference,AppendixAprovidesaglossaryoftermsusedinthismanual. AppendixBprovidesmoredetailed
information on methods of measuring fatigue as part of the FRM processes presented in Chapter Three.
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AppendixCalsosupportsChapterThreebyprovidingfurtherinformationontheuseofcontrolledrestonthe
flightdeckasamitigatoroffatiguerisk.
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ChapterTwo:ScienceforFRMS
2.1IntroductiontoScienceforFRMSThe FRMS approach represents an opportunity for operators to use advances in scientific knowledge toimprove safety and increase operational flexibility. This chapter reviews the scientific principles needed todevelopandimplementaneffectiveFRMS.
InChapterOne,theICAOdefinitionofcrewmemberfatiguewasgivenas:
Aphysiological state of reducedmental orphysicalperformance capability resultingfrom sleep loss or
extendedwakefulness, circadianphase, orworkload (mental and/orphysical activity) that can impair a
crewmembersalertnessandabilitytosafelyoperateanaircraftorperformsafetyrelatedduties.
Inflightoperations,fatiguecanbemeasuredeithersubjectivelybyhavingcrewmembersratehowtheyfeel,orobjectivelybymeasuringcrewmembersperformance(ChapterFourandAppendixB).
Anotherwayofthinkingaboutthisisthatfatigueisastatethatresultsfromanimbalancebetween:
thephysicalandmentalexertionofallwakingactivities(notonlydutydemands);and recoveryfromthatexertion,which(exceptforrecoveryfrommusclefatigue)requiressleep.
Following this line of thinking, to reduce crewmember fatigue requires reducing the exertion of wakingactivitiesand/orimprovingsleep.TwoareasofsciencearecentraltothisandarethefocusofthisChapter.
1. Sleepscienceparticularlytheeffectsofnotgettingenoughsleep(ononenightoracrossmultiplenights),andhowtorecoverfromthem;and
2. Circadianrhythmsthestudyofinnaterhythmsdrivenbythedailycycleofthecircadianbiologicalclock(apacemakerinthebrain).Theseinclude: rhythmsinsubjectivefeelingsoffatigueandsleepiness;and rhythms intheabilitytoperformmentalandphysicalwork,whichaffecttheeffortrequiredtoreach
anacceptablelevelofperformance(exertion);and rhythmsinsleeppropensity(theabilitytofallasleepandstayasleep),whichaffectrecovery.
2.2EssentialSleepScienceThere isawidespreadbelief thatsleep timecanbe tradedoff to increase theamountof timeavailable forwakingactivitiesinabusylifestyle.Sleepsciencemakesitveryclearthatsleepisnotatradablecommodity.
2.2.1WhatisHappeningintheBrainDuringSleepThereareavarietyofwaysoflookingatwhatishappeninginthesleepingbrain,fromreflectingondreamstousing advanced medical imaging techniques. Currently, the most common research method is known aspolysomnography (see Appendix B for details). This involves sticking removable electrodes to the scalp and
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face and connecting them to a recording device, to measure three different types of electrical activity: 1)brainwaves(electroencephalogramorEEG);2)eyemovements(electroculogramorEOG);and3)muscletone(electromyogramorEMG). Usingpolysomnography,itispossibletoidentifytwoverydifferentkindsofsleep.
NonRapidEyeMovementSleep
Comparedtowakingbrainactivity,nonRapidEyeMovementsleep(nonREMsleep)involvesgradualslowingofthebrainwaves.Theamplitude(height)ofthebrainwavesalsobecomeslargerastheelectricalactivityof
largenumbersofbraincells(neurons)becomessynchronizedsothattheyfireinunison.Heartrateandbreathingtendtobeslowandregular.
PeoplewokenfromnonREMsleepdonotusuallyrecallmuchmentalactivity.However,itisstillpossibleforthebodytomoveinresponsetoinstructionsfromthebrain. Becauseofthesefeatures,nonREMsleepissometimesdescribedasarelativelyinactivebraininamovablebody.
NonREMsleepisusuallydividedinto4stages,basedonthecharacteristicsofthebrainwaves.
Stages1and2representlightersleep(itisnotverydifficulttowakesomeoneup).ItisusualtoentersleepthroughStage1andthenStage2nonREM.
Stages 3 and 4 represent deeper sleep (it can be very hard to wake someone up). Stages 3 and 4 arecharacterizedbyhighamplitudeslowbrainwaves,andaretogetheroftendescribedasslowwavesleep(ordeepsleep).
Slowwavesleephasanumberofimportantproperties.Pressureforslowwavesleepbuildsupacrosswakinganddischargesacrosssleep.Inotherwords:
thelongeryouareawake,themoreslowwavesleepyouwillhaveinyournextsleepperiod;and acrossasleepperiod,theproportionoftimespentinslowwavesleepdecreases.
Thisrisingandfallingofpressureforslowwavesleepissometimescalledthesleephomeostaticprocess,andit
isacomponent
in
most
of
the
bio
mathematical
models
that
are
used
to
predict
crewmember
fatigue
levels
(seeChapterFour).
Eveninslowwavesleep,thebrainisstillabout80%activatedandcapableofactivecognitiveprocessing.Thereisgrowingevidencethatslowwavesleep isessential for theconsolidationofsometypesofmemory,and isthereforenecessaryforlearning.
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RapidEyeMovementSleep
DuringRapidEyeMovementsleep(REMsleep),brainactivitymeasuredbypolysomnography lookssimilartobrainactivityduringwaking.However inREMsleep,fromtimetotimetheeyesmovearoundundertheclosedeyelidsthesocalledrapideyemovementsandthisisoftenaccompaniedbymuscletwitchesandirregularheartrateandbreathing.
PeoplewokenfromREMsleepcantypicallyrecallvividdreaming.Atthesametime,thebodycannotmoveinresponsetosignalsfromthebrainsodreamscannotbeactedout.(Thesignalseffectivelygetblockedinthe
brainstemandcannotgetthroughtothespinalcord.)Peoplesometimesexperiencebriefparalysiswhentheywakeupoutofadream,whenreversalofthisREMblockisslightlydelayed.Becauseofthesefeatures,REMsleepissometimesdescribedasahighlyactivatedbraininaparalysedbody.
Dreams have always been a source of fascination, but are difficult to study using quantitative scientificmethods.Theyhavebeeninterpretedaseverythingfromspiritualvisitationstofulfillmentofinstinctualdrives,tobeingameaninglessbyproductofactivityinvariouspartsofthebrainduringREMsleep.Thecurrentneurocognitiveviewofdreamingarguesthatitresultsfrombriefmomentsofconsciousnesswhenwebecomeawareofalltheprocessingthatourbrainsnormallydooffline,i.e.whentheyarenotbusydealingwithinformation
OperationalNote:MitigationStrategiesforSleepInertia
Operationally, slowwave sleep may be important because the brain can havedifficultytransitioningoutofitwhensomeoneiswokenupsuddenly.Thisisknown
assleep
inertia
feelings
of
grogginess
and
disorientation,
with
impaired
short
term
memory and decisionmaking. Sleep inertia can occur coming out of lighter sleep,but it tends tobe longerandmoredisorientingwhensomeone iswokenabruptlyoutofslowwavesleep.
Thisissometimesusedasanargumentagainsttheuseofflightdecknappingorinflight sleep. It would not be desirable to have a crewmember who is woken upbecause of an emergency, but who is impaired by sleep inertia. This argument isbasedontheeffectsofsleepinertiaseeninlaboratorystudies.
However,studiesofnappingon the flight deck andofsleep in onboardcrew restfacilitiesshowthatsleep inflightcontainsvery littleslowwavesleep. (It is lighter
and more fragmented than sleep on the ground). This means that sleep inertia ismuch less likely to occur waking up from sleep in flight than would be predictedfromlaboratorysleepstudies.Theriskofsleepinertiacanalsobereducedbyhavingaprotocolforreturningtoactivedutythatallowstimeforsleepinertiatowearoff.
Overall,thedemonstratedbenefitsofcontrollednappingandinflightsleepgreatlyoutweigh the potential risks associated with sleep inertia. To reduce the risk ofsleep inertia after flight deck napping, the recommendation is to limit the timeavailableforthenapto40minutes.Giventhetimetakentofallasleep,a40minuteopportunity is too short for most people to enter slowwave sleep. Refer toAppendix C for suggested Flight Operations Manual procedures for controllednapping.
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cominginfromtheenvironmentthroughthesenses,andarenotbeingdirectedbyourconsciouscontrol.Thisofflineprocessingincludesreactivatingmemoriesandemotionsfrompreviousexperiences,and integratingthem with experiences from the latest period of waking. Dreams in this view are a glimpse into your brainreshapingitselfsothatyoucanwakeupinthemorningstillyourself,butaslightlyrevisedversionasaresultofyourexperiencesyesterday,andreadytostartinteractingwiththeworldagain.
People vary greatly in their ability to recall dreams, and we generally only recall them when we wake
spontaneouslyout of REM sleep (and then only fleetingly unless we write them down or talk about them).Nevertheless,mostadultsnormallyspendaboutaquarteroftheirsleeptimeinREMsleep.
NonREM/REMCycles
Acrossanormalnightofsleep,nonREMsleepandREMsleepalternateinacyclethatlastsroughly90minutes(butisveryvariableinlength,dependingonanumberoffactors).Figure2.1isadiagramdescribingthenonREM/REMcycleacrossthenight inahealthyyoungadult.Realsleep isnotas tidyas this it includesmorearousals(transitionstolightersleep)andbriefawakenings. Sleepstagesareindicatedontheverticalaxisandtimeisrepresentedacrosshorizontalaxis3.
Figure2.1:DiagramofthenonREM/REMcycleacrossthenightinayoungadult
SleepisenteredthroughStage1nonREMandthenprogressesdeeperanddeeperintononREM.About8090minutesintosleep,thereisashiftoutofslowwavesleep(nonREMstages3and4).Thisisoftenmarkedby
bodymovements,
as
the
sleeper
transitions
briefly
through
Stage
2non
REM
and
into
the
first
REM
period
of
thenight. (REMperiodsare indicatedasshadedboxes inFigure2.1).Aftera fairlyshortperiodofREM, thesleeperprogressesbackdownagainthroughlighternonREMsleepandintoslowwavesleep,andsothecyclerepeats.
3GanderPH(2003)Sleepinthe24HourSociety.Wellington,NewZealand:OpenMindPublishing.ISBN0909009597
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The amount of slowwave sleep in each nonREM/REM cycle decreases across the night, and there may benone at all in the later cycles. In contrast, the amount of REM sleep in each nonREM/REM cycle increasesacrossthenight.ThesleeperdepictedinFigure2.1wakesupdirectlyoutofthefinalREMperiodofthenight,andsowouldprobablyrecalldreaming.
Interestingly, slowwave sleep always predominates at the beginning of a sleep period, regardless of whensleep occurs in the day/night cycle or in the circadian body clock cycle. There seems to be a priority to
dischargethehomeostaticsleep
pressurefirst.Incontrast,thetimefromsleeponsettothefirstboutofREM
(theREM latency)andthedurationofeachREMboutvariesmarkedlyacrossthecircadianbodyclockcycle.ThecircadiandriveforREMsleepisstrongestafewhoursbeforenormalwakeuptime.Thesetwoprocessesthe homeostatic sleep process and the circadian body clock are the main components in most of the biomathematicalmodelsthatareusedtopredictcrewmemberfatiguelevels(seeChapterFour).
2.2.2TheIssueofSleepQualitySleepquality(itsrestorativevalue)dependsongoingthroughunbrokennonREM/REMcycles(whichsuggeststhat both types of sleep are necessary and one is not more important than the other). The more the nonREM/REMcycle is fragmented by wakingup, or by arousals that move the brain to a lighter stage of sleepwithoutactuallywakingup,thelessrestorativevaluesleephasintermsofhowyoufeelandfunctionthenextday.
OperationalNote:MitigationStrategiesforSleepLoss
RestorationofanormalnonREM/REMcycle isonemeasureof recovery from the
effects of sleep loss. Lost sleep is not recovered hourforhour, although recoverysleepmaybeslightlylongerthanusual.
On the first recoverynight, there ismoreslowwavesleep thanusual. Indeed,therecanbesomuchslowwavesleepthatthereisnotenoughtimetomakeupREMsleep.
Onthesecondrecoverynight,thereisoftenmoreREMsleepthanusual. Bythethirdrecoverynight,thenonREM/REMcycleisusuallybacktonormal.
Operationally,thismeansthatschedulesneedtoperiodicallyincludeanopportunityforatleasttwoconsecutivenightsofunrestrictedsleep,toenablecrewmemberstorecoverfromtheeffectsofsleeploss.
This does not equate to 48 hours off. For example, 48 hours off duty starting at02:00wouldonlygivemostpeopletheopportunityforonefullnightofunrestrictedsleep.Ontheotherhand,40hoursoffstartingat21:00wouldgivemostpeopletheopportunityfortwofullnightsofunrestrictedsleep.
Additional nights may be needed for recovery if a crewmembers circadian bodyclockisnotalreadyadaptedtothelocaltimezone(seeSection2.3).
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QualityofInFlightSleep
Asmentionedabove,polysomnographystudiesshowthatcrewmemberssleepinonboardcrewrestfacilitiesislighterandmorefragmentedthansleepontheground4.Sleepduringflightdecknapsisalsolighterandmorefragmented thanwouldbepredicted from laboratorystudies5.Nevertheless, there isgoodevidence that inflightsleepimprovessubsequentalertnessandreactionspeedandisavaluablemitigationstrategyinanFRMS.
Interestingly, studies of sleep in hypobaric chambers at pressures equivalent to cabin pressure at cruisingaltitudeindicatethatthefragmentedqualityofinflightsleepisnotduetoaltitude6.Severalstudieshaveaskedcrewmemberswhatdisturbs theirsleeponboard.The factorsmostcommonly identifiedare random noise,thoughts,notfeelingtired,turbulence,ambientaircraftnoise,inadequatebedding,lowhumidity,andgoingtothetoilet.
SleepQualityandAging
Acrossadulthood,theproportionofsleeptimespentinslowwavesleepdeclines,particularlyamongmen.Inaddition, sleep becomes more fragmented. For example, one study with 2,685 participants aged 3792 yrs
4Signal,T.L.,Gale,J.,andGander,P.H.(2005)SleepMeasurementinFlightCrew:ComparingActigraphicandSubjectiveEstimatesof
SleepwithPolysomnography.AviationSpaceandEnvironmentalMedicine76(11):105810635Rosekind,M.R.,Graeber,R.C.,Dinges,D.F.,etal.,(1994)CrewFactorsinFlightOperationsIX:Effectsofplannedcockpitrestoncrewperformanceandalertnessinlonghauloperations.NASATechnicalMemorandum108839,MoffettField:NASAAmesResearchCenter.6Mumm,J.M.,Signal,T.L.,Rock,P.B.,Jones,S.P.,OKeeffe,K.M.,Weaver,M.R.,Zhu,S.,Gander,P.H.,Belenky,G.(2009)Sleepat
simulated2438m:effectsonoxygenation,sleepquality,andpostsleepperformance.Aviation,Space,andEnvironmentalMedicine80(8):691697.
OperationalNote:MitigationStrategiestoMinimizeSleepInterruptions
Because uninterrupted nonREM/REM cycles are the key to good quality sleep,
operatorsshould
develop
procedures
that
minimize
interruptions
to
crewmembers
sleep.
Rest periods should include defined blocks of time (sleep opportunities) duringwhich crewmembers are not contacted except in emergencies. These protectedsleep opportunities need to be known to flight crews and all other relevantpersonnel.Forexample,calls fromcrewschedulingshouldnotoccurduringa restperiodastheycanbeextremelydisruptive.
Operatorsshouldalsodevelopprocedurestoprotectcrewmembersleepatlayoverand napping facilities. For example, if a rest period occurs during the day at alayover hotel, the operator could make arrangements with the hotel to restrict
accessto
the
section
of
the
hotel
where
crewmembers
are
trying
to
sleep
(such
as
nochildren,crewmembersonly)andinstructtheirstafftohonorthenecessaryquietperiods(forexample,nomaintenanceworkorroutinecleaning).
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foundthattheaveragenumberofarousals(transitionstolightersleepandawakenings)rosefrom16perhourofsleepfor3054yearoldsto20perhourofsleepfor6170yearolds7.
Theseagerelatedtrendsareseeninthesleepofflightcrewmembers,bothonthegroundandintheair2,8.AstudyofinflightsleepondeliveryflightsofB777aircraft(fromSeattletoSingaporeorKualaLumpur)foundthatagewasthefactorthatmostconsistentlypredictedthequalityanddurationofbunksleep.Olderpilotstooklongertofallasleep,obtainedlesssleepoverall,andhadmorefragmentedsleep.
It is not yet clear whether these agerelated changes in sleep reduce its effectiveness for restoring wakingfunction.Laboratorystudiesthatexperimentallyfragmentsleeparetypicallyconductedwithyoungadults.Ontheflightdeck,experience(bothintermsofflyingskillsandknowinghowtomanagesleepontrips)couldhelpreducepotentialfatigueriskassociatedwithagerelatedchangesinsleep.
SleepDisorders
Thequalityofsleepcanalsobedisruptedbyawidevarietyofsleepdisorders,whichmake it impossible toobtain restorative sleep, even when people spend enough time trying to sleep. Sleep disorders pose aparticularriskforflightcrewmembersbecause,inaddition,theyoftenhaverestrictedtimeavailableforsleep.It isrecommended thatFRMStraining (ChapterSix)should includebasic informationonsleepdisordersandtheirtreatment,wheretoseekhelpifneeded,andanyrequirementsrelatingtofitnesstofly.
2.2.3ConsequencesofNotGettingEnoughSleepEvenforpeoplewhohavegoodqualitysleep,theamountofsleeptheyobtainisveryimportantforrestoringtheirwakingfunction.Anincreasingnumberoflaboratorystudiesarelookingattheeffectsoftrimmingsleepatnightbyanhourortwo(knownassleeprestriction).ThereareseveralkeyfindingsfromthesestudiesthatareimportantforFRMS.
1. Theeffectsofrestrictingsleepnightafternightaccumulate,sothatpeoplebecomeprogressivelylessalertand less functional day after day. This is sometimes described as accumulating a sleep debt. This is acommon occurrence for crewmembers (see below), for example when minimum rest periods are
scheduledforseveraldaysinarow.
2. The shorter the time allowed for sleep each night, the faster alertness and performance decline. Forexample,onelaboratorystudyfoundthatspending7hoursinbedfor7consecutivenightswasnotenoughto prevent a progressive slowing down in reaction time9. The decline was more rapid for a group ofparticipantswhospentonly5hoursinbedeachnight,andevenmorerapidforagroupwhospentonly3hoursinbedeachnight.Thisisdescribedasadosedependenteffectofsleeprestriction.
3. The pressure for sleep increases progressively across successive days of sleep restriction. Eventually, itbecomesoverwhelmingandpeoplebeginfallingasleepuncontrollablyforbriefperiods,knownasmicrosleeps. During a microsleep, the brain disengages from the environment (it stops processing visualinformation and sounds). In the laboratory, this can result in missing a stimulus in a performance test.Drivingamotorvehicle,itcanresultinfailingtotakeacorner.Similareventshavebeenrecordedontheflightdeckduringdescentintomajorairports5.
7Redline,S.,Kirchner,H.L.,Quan,S.F.,Gottlieb,D.J.,Kapur,V.,Newman,A.(2004).Theeffectsofage,sex,ethnicity,andsleep
disorderedbreathingonsleeparchitecture.ArchivesofInternalMedicine164:406418.8Signal,T.L.,Gander,P.H.,vandenBerg,M.(2004)Sleepinflightduringlongrestopportunities.InternalMedicineJournal34(3):A38.
9Belenky,G.,Wesensten,N.J.,Thorne,D.R.,etal.(2003).Patternsofperformancedegradationandrestorationduringsleeprestrictionand
subsequentrecovery:asleepdoseresponsestudy.JournalofSleepResearch12:112.
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4. Fullrecoveryofwakingfunctionaftersleeprestrictioncantakelongerthantwonightsofrecoverysleep(i.e., longerthan ittakesthenonREM/REMcycletorecover). Indeed,chronicsleeprestrictionmayhaveeffectsonthebrainthatcanaffectalertnessandperformancedaystoweekslater10.
5. Forthefirstfewdaysofseveresleeprestriction(forexample,3hoursinbed),peopleareawarethattheyare getting progressively sleepier. However, after several days they no longer notice any difference inthemselves,evenalthoughtheiralertnessandperformancecontinuestodecline.Inotherwords,assleep
restrictioncontinues,peoplebecomeincreasinglyunreliableatassessingtheirownfunctionalstatus.Thisfindingraisesaquestionaboutthereliabilityofsubjectiveratingsoffatigueandsleepinessasmeasuresofacrewmembersleveloffatiguerelatedimpairment(seeAppendixB).
6. At least in the laboratory,somepeoplearemoreresilienttotheeffectsofsleeprestriction thanothers.Currently,thereisalotofresearcheffortaimedattryingtounderstandwhythisis,butitisstilltooearlyforthistobeappliedinanFRMS(forexample,byrecommendingdifferentpersonalmitigationstrategiesforpeoplewhoaremoreorlessaffectedbysleeprestriction).
Ingeneral,morecomplexmentaltaskssuchasdecisionmakingandcommunicationseemtobemoreseverelyaffectedbysleeplossthansimplertasks.Brainimagingstudiesalsosuggestthatthebrainregionsinvolvedin
morecomplex
mental
tasks
are
the
most
affected
by
sleep
deprivation
and
have
the
greatest
need
for
sleep
to
recovertheirnormalfunction.
Laboratory sleep restriction studies are currently the main source of information on the effects of sleeprestriction.However, they have some obvious limitations. The consequences of reduced alertnessandpoortask performance are quite different in the laboratory than for crewmembers on duty. Laboratory studiesusuallylookattheeffectsofrestrictingsleepatnightandparticipantssleepinadark,quietbedroom.Thismaymeanthatcurrentunderstandingisbasedonabestcasescenario.Moreresearchisneededontheeffectsofrestrictingsleepduringtheday,andonthecombinationofrestrictedsleepandpoorqualitysleep.Laboratorystudiesalsofocusontheperformanceofindividuals,notpeopleworkingtogetherasacrew.
One simulation study with 67 experienced B747400 crews has demonstrated that sleep loss increased thetotalnumberoferrorsmadeby thecrew11.Thestudydesignwassetupso that thepilot incommand wasalways the pilot flying. Paradoxically, greater sleep loss among first officers improved the rate of errordetection.Ontheotherhand,greatersleeplossamongpilotsincommandledtoahigherlikelihoodoffailureto resolve errors that had been detected. Greater sleep loss was also associated with changes in decisionmaking,includingatendencytochooselowerriskoptions,whichwouldhelpmitigatethepotentialfatiguerisk.Simulatorstudies like this areexpensiveand logisticallycomplex toconductproperly,but theyprovidevitalinsightsonthelinksbetweencrewmembersleepandoperationalfatiguerisk.
SleepRestrictioninFlightOperations
Theideaofsleeprestrictionimpliesthatthereisanoptimumamountofsleepthatpeopleneedtoobtaineachnight.Theconceptofindividualsleepneedisanareaofactivedebateinsleepresearch.Onewaytomeasure
sleeprestrictionthatavoidsthisproblemistolookathowmuchsleepcrewmembersobtainwhentheyareathomebetweentrips,comparedtohowmuchsleeptheyobtainduringtrips.
10Rupp,T.L.,Wesensten,N.J,Bliese,P.D.etal.(2009).Bankingsleep:realizationofbenefitsduringsubsequentsleeprestrictionand
recovery.Sleep32(3):31132111 Thomas, M.J.W., Petrilli, R.M., Lamond, N.A., et al. (2006). Australian Long Haul Fatigue Study. In: Enhancing SafetyWorldwide:
Proceedingsofthe59thAnnualInternationalAirSafetySeminar.Alexandria,USA,FlightSafetyFoundation.
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Table2.1summarizesdataonsleeprestrictionacrossdifferent flightoperationsthatweremonitoredbytheNASAFatiguePrograminthe1980s12.Inthesestudies,crewmemberscompletedsleepanddutydiariesbefore,during,andafterascheduledcommercialtrip.Foreachcrewmember,hisaveragesleepdurationper24hoursathomebeforethetripwascomparedwithhisaveragesleepdurationper24hoursonthestudytrip.Duringnightcargoandlonghaultrips,crewmembersoftenhadsplitsleep(sleptmorethanoncein24hours).
Scheduling has undoubtedly changed since these studies, so the data in Table 2.1 are likely to be
unrepresentativeofthecurrentsituation inmanycases.However,they indicatethatsleeprestriction isverycommonacrossdifferenttypesofflightoperations.
Table2.1:Sleeprestrictionduringcommercialflightoperations
ShortHaul NightCargo LongHaul
crewmembersaveragingatleast1hourofsleeprestrictionpertripday
67% 54% 43%
crewmembersaveragingatleast2
hoursofsleeprestrictionpertripday
30% 29% 21%
lengthoftrip 34days 8days 49days
timezonescrossedperday 01 01 08
numberofcrewmembersstudied 44 34 28Note:thenightcargotripsincludeda12nightbreakinthesequenceofnightshifts.Splittinglonghaultripsinto24hoursdaysisratherarbitrary,becausetheaveragedutydaylasted10.2hoursandtheaveragelayoverlasted24.3hours.
Agrowingamountofevidence,frombothlaboratorystudiesandfromepidemiologicalstudiesthattrackthe
sleepand
health
of
large
numbers
of
people
across
time,
indicates
that
chronic
short
sleep
may
have
negative
effectsonhealth inthe longterm.Thisresearchsuggeststhatshortsleepersareatgreaterriskofbecomingobeseanddevelopingtype2diabetesandcardiovasculardisease.Thereisstilldebateaboutwhetherhabitualshortsleepactuallycontributes to thesehealthproblems,or isjustassociatedwith them. Inaddition, flightcrewmembersasagroupareexceptionallyhealthycomparedtothegeneralpopulation.Whatisclearisthatgoodhealthdependsnotonlyongooddietandregularexercise,butalsoongettingenoughsleeponaregularbasis. Sleepisdefinitelynotatradablecommodity.
12Gander,P.H.,Rosekind,M.R.,andGregory,K.B.(1998)FlightcrewfatigueVI:anintegratedoverview.Aviation,Space,andEnvironmental
Medicine69:B49B60
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2.3IntroductiontoCircadianRhythmsSleepingatnight isnotjustasocialconvention. It isprogrammed intothebrainbythecircadianbodyclock,which is an ancient adaptation to life on our 24hour rotating planet. Even very ancient types of livingorganisms have something equivalent, which means that circadian biological clocks have been around forseveralbillionyears.
Afeatureofcircadianclocksisthattheyarelightsensitive.Thehumancircadianclockmonitorslightintensitythroughaspecialnetworkofcellsintheretinaoftheeye(thisspeciallightinputpathwaytothecircadianclockisnotinvolvedinvision).Theclockitselfresidesinafairlysmallclusterofcells(neurons)deeperinthebrain(inthe suprachiasmatic nuclei (SCN) of the hypothalamus). The cells that make up the clock are intrinsicallyrhythmic, generating electrical signals faster during the day than during the night. However, they have atendencytoproduceanoverallcyclethatisabitslowformostpeoplethebiologicaldaygeneratedbythe
circadianbodyclockisslightlylongerthan24hours.Thesensitivityofthecircadianbodyclocktolightenablesit to stay instepwith the day/nightcycle. However, thatsamesensitivity to lightalso createsproblems forcrewmemberswhohavetosleepoutofstepwiththeday/nightcycle (forexampleondomesticnightcargooperations),orwhohavetoflyacrosstimezonesandexperiencesuddenshiftsintheday/nightcycle.
2.3.1ExamplesofCircadianRhythmIt is not possible to directly measure the electrical activity of the circadian body clock in human beings.However, almost every aspect of human functioning (physical or mental) undergoes daily cycles that are
OperationalNote:MitigationStrategiesforManagingSleepDebt
Sleeprestrictioniscommonacrossdifferenttypesofflightoperations.Becausethe
effects
of
sleep
restriction
are
cumulative,
schedules
must
be
designed
to
allow
periodic opportunities for recovery. Recovery opportunities need to occur morefrequently when daily sleep restriction is greater, because of the more rapidaccumulationoffatigue.
The usual recommendation for a recovery opportunity is for a minimum of twoconsecutive nights of unrestricted sleep. Some recent laboratory studies of sleeprestrictionsuggestthat thismaynotbeenough tobringcrewmembersbackup totheiroptimal levelof functioning.There isevidence that thesleeprestrictedbraincanstabilizeatalowerleveloffunctioningforlongperiodsoftime(daystoweeks).
Especiallyinirregularoperations,proceduresthatallowacrewmembertocontinue
sleeping
until
needed
can
reduce
the
rate
of
accumulation
of
sleep
debt.
For
example, ifanaircraftwithananticipated repair timeof0730willnotactuallybeready until 11:30, then a reliable procedure that allows the crew member tocontinuesleepingwouldbebeneficial.Oneairlinehasasystemwheretheoperatorcontacts the layoverhotel toupdate the report time byslipping amessage underthecrewmembersdoor.Thehotelprovidesawakeupcallonehourbeforepickuptime.
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influencedbythecircadianbodyclock. Measuringovertrhythmsinphysiologyandbehaviourislikewatchingthehandsofan(analogue)wristwatch.Thehandsmovearoundthewatchfacebecausetheyaredrivenbythetimekeeping mechanism inside the watch, but they are not part of the timekeeping mechanism itself.Similarly,most circadian rhythms that canbemeasured,such as rhythms in core body temperatureor selfrated fatigue, are driven by the circadian body clock, but they are not part of the biological timekeepingmechanism.
Figure2.2showsanexampleofcircadianrhythmsincorebodytemperatureandselfratedfatigueofa46yearoldshorthaulcrewmembermonitoredbefore,during,andaftera3daypatternofflyingontheeastcoastoftheUSA(stayinginthesametimezone)13. Thecrewmemberhadhiscoretemperaturemonitoredcontinuouslyandkeptasleepanddutydiary,inwhichhenotedhissleeptimesandratedthequalityofhissleep,aswellasratinghisfatigueevery2hourswhilehewasawake(onascalefrom0=mostalertto100=mostdrowsy).
Corebodytemperaturetypicallyfluctuatesbyabout1 Cacrossthe24hourday.Notethatthecrewmember'scoretemperaturestartstoriseeachmorningbeforehewakesup. Ineffect,hisbody isbeginningtoprepareaheadoftimeforthegreaterenergydemandsofbeingmorephysicallyactive.(Ifbodytemperatureonlybegantoriseafterhestartedtobemorephysicallyactive,itwouldbealothardertogetupinthemorning).
Lookingat
his
self
rated
fatigue,
this
crewmember
did
not
feel
at
his
best
first
thing
in
the
morning.
He
tended
tofeelleastfatiguedabout24hoursafterhewokeup,afterwhichhisfatigueclimbedsteadilyacrosstheday.Thedashedlineacrossthesleepperiodindicatesthathewasnotaskedtowakeupevery2hourstoratehisfatigueacrossthistime.
Figure2.2:Circadianrhythmsofashorthaulpilot
13Gander,P.H.,Graeber,R.C.,Foushee,H.C.,Lauber,J.K.,Connell,L.J.(1994).CrewFactorsinFlightOperationsII:Psychophysiological
ResponsestoShortHaulAirTransportOperations.NASATechnicalMemorandum#108856.MoffettField:NASAAmesResearchCenter.
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Corebodytemperatureisoftenuseasamarkerrhythmtotrackthecycleofthecircadianbodyclockbecauseitisrelativelystableandeasytomonitor.However,nomeasurablerhythm isaperfectmarkerofthecircadianbodyclockcycle.Forexample,changesinthelevelofphysicalactivityalsocausechangesincoretemperature,whichexplainsthesmallpeaksanddipsintemperatureinFigure2.2.
Thedailyminimumincorebodytemperaturecorrespondstothetimeinthecircadianbodyclockcyclewhenpeoplegenerallyfeelmostsleepyandare leastabletoperformmentalandphysicaltasks.This issometimes
describedastheWindowof
Circadian
Low
(WOCL).
2.3.2TheCircadianBodyClockandSleepAsmentionedinSection2.2,thecircadianbodyclockinfluencessleepinanumberofways.(Ithasconnectionstocentersinthebrainthatpromotewakefulnessandtoopposingcentersthatpromotesleep,aswellastothesystemthatcontrolsREMsleep.) Figure2.3isadiagramthatsummarizestheeffectsofthecircadianclockonsleep.Itisbasedondatacollectedfrom18nightcargopilotsontheirdaysoff,i.e.,whentheyweresleepingatnight14.LikethecrewmemberinFigure2.2,theyalsohadtheircoretemperaturemonitoredcontinuously,andkeptsleepanddutydiaries.
Thecore
temperature
rhythm
issummarized
as
asimple
(continuous)
curve.
The
daily
time
of
the
minimum
in
temperature(shownbytheblackdot)istheaverageforallcrewmembersandisusedasareferencepointfordescribingtheotherrhythms.Notethatchangesintemperaturearenotthecauseoftheotherrhythms.Thecorebodytemperaturerhythmisbeingreadlikethehandsofananaloguewristwatch,asawayoffollowingtheunderlyingcycleofthecircadianbodyclock.
Figure2.3:Summaryoftheinfluencesofthecircadianbodyclockonsleepatnight
14Gander,P.H.,Rosekind,M.R.,andGregory,K.B.(1998)FlightcrewfatigueVI:anintegratedoverview.Aviation,
Space,andEnvironmentalMedicine69:B49B60
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Figure2.3summarizesthefollowingfeaturesofsleepatnight(whencrewmembersarefullyadaptedtothelocaltimezone).
Sleepnormallybeginsabout5hoursbeforetheminimumincorebodytemperature. Wakeupnormallyoccursabout3hoursaftertheminimumincorebodytemperature. REMsleep isentered fastest,andREMperiodsare longestandmost intense,justafter theminimum in
core body temperature. This is sometimes described as the peak of the circadian rhythm in REMpropensity(thedashedcurveinFigure2.3).
Avarietyoflaboratoryprotocolshavedemonstratedpeopleareextremelyunlikelytofallasleep68hoursbeforetheminimumincorebodytemperature.Thishasbecomeknownastheeveningwakemaintenancezone.
Laboratorystudiesalsoshow thatasbody temperaturebegins to rise,there isan increasingpressuretowakeup.Thispeaksabout6hoursafterthecircadiantemperatureminimum.Thisissometimesreferredtoas an internal alarm clock, because it is very hard to fall asleep or stay asleep during this part of thecircadianbodyclockcycle.
Theinteractionbetweenthehomeostaticpressureforsleepandthecircadianvariationinsleepinessdrivenby
thebodyclock resultsintwotimes
of
peak
sleepiness
in
24
hours;
apeakintheearlyhoursofthemorningthesocalledWindowofCircadianLow(WOCL),whichoccursaround35amformostpeople;and
a peak in the early afternoon sometimes called the afternoon nap window (around 35 pm for mostpeople). Restricted sleep at night, or disturbed sleep makes it harder to stay awake during the nextafternoonnapwindow.
The precise timing of the two peaks in sleepiness is different in people who are morning types (whosecircadian rhythms and preferred sleep times are earlier than average) and evening types (whose circadianrhythms and preferred sleep times are later than average). Across the teenage years, most people become
more eveningtype. Across adulthood, most people become more morningtype. This progressive changetowardsbecomingmoremorningtypehasbeendocumentedinflightcrewmembersacrosstheagerange2060years.
Thecombinedeffectsofthehomoeostaticpressureforsleepandthecircadianbiologicalclockcanbethoughtofasdefiningwindowswhensleepispromoted(theearlymorningandafternoontimesofpeaksleepiness)andwindowswhensleepisopposed(thetimeoftheinternalalarmclockinthelatemorning,andtheeveningwakemaintenancezone).
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2.3.3SensitivityoftheCircadianBodyClocktoLightAtthebeginningofthisChapter,therewasabriefdescriptionofhowthecircadianbodyclockisabletotracklightintensityintheenvironment.Thisenablesittostayinstepwiththeday/nightcycle,evenalthoughithasatendencytogenerateabiologicaldaythatisslightlylongerthan24hours.
Theeffect
of
light
on
the
circadian
body
clock
changes
according
to
when
in
the
clock
cycle
the
light
exposure
occurs.Foracrewmemberadaptedtolocaltimeandsleepingatnight:
light exposure in the morning (after the temperature minimum) causes the circadian clock to speed uptemporarily,resultinginaphaseadvance(equivalenttocrossingtimezonesinaneastwarddirection);
lightexposureinthemiddleofthedayhasverylittleeffect;and lightexposureintheevening(beforethetemperatureminimum)causesthecircadianclocktoslowdown
temporarily,resultinginaphasedelay(equivalenttocrossingtimezonesinawestwarddirection).
OperationalNote:TheCircadianBodyClock,Sleep,andFRMS
The daily minimum in core body temperature corresponds to the time in thecircadian body clock cycle when people feel most sleepy and are least able to
perform
mental
and
physical
tasks.
This
is
sometimes
called
the
Window
of
CircadianLow(WOCL)anditisatimeofhighriskforfatiguerelatederror.InFRMSincidentinvestigations,itisimportanttoestimatethetimethaterrorsoccurrelativetotheexpectedtimeoftheWOCL.
TheWOCLcanoccurinflightduringdomesticnightoperationsandduringlonghauland ULR operations when the duty/rest cycle is out of step with crewmemberscircadianbodyclockcycles.
Theeveningwakemaintenancezoneoccursinthefewhoursbeforeusualbedtime.Thismakesitverydifficulttofallasleepearlythenightbeforeanearlydutyreporttime.Thishasbeenidentifiedacauseofrestrictedsleepandincreasedfatiguerisk
inshorthauloperationsthatrequireearlystarts.
The increasing drive for wake that accompanies the increase in core bodytemperatureinthemorningmakesitdifficulttofallasleeporstayasleeplaterinthemorningandintheearlyafternoon.Thishasbeenidentifiedasacauseofrestrictedsleep and increased fatigue risk in night cargo operations, which requirecrewmemberstodelaytheirmainsleepperioduntilthemorning.
The internal alarm clock and the evening wake maintenance zone can alsointerfere with the inflight sleep and layover sleep of long haul and ULRcrewmemberswhentheduty/restcycleisoutofstepwithcrewmemberscircadian
bodyclockcycles.
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Bright lightcausesbiggershifts in thecircadianbodyclockcycle thandim light,and theclock isparticularlysensitivetobluelight.Intheory,thismeansthatjusttherightamountoflightexposureatthesametimeeverymorningwouldspeedupa24.5hourcircadianclockcyclejustenough tosynchronize it toexactly24hours. Inpractise,staying instepwiththeday/nightcycleismorecomplexthanthis. Inmodern industrialisedsocieties,peoplehaveveryhaphazardexposurestolight,particularlybrightoutdoorlight.Inaddition,thecircadianbodyclockissensitivetoothertimecuesfromtheenvironment,notablysocialcues,andcanalsobemovedbackwardsorforwardsin
itscyclebyboutsofphysicalactivity.
Theabilityofthecircadianclocktolockontothe24hourday/nightcycleisakeyfeatureofitsusefulnessformostspecies,enablingthemtobediurnalornocturnalasneededtoenhancetheirsurvival.However, ithasbecome a disadvantage in the 24/7 society because it causes the human circadian body clock to resistadaptationtoanypatternotherthansleepatnight.
2.3.4ShiftWorkFrom the perspective of human physiology, shift work can be defined as any duty pattern that requires acrewmembertobeawakeduringthetimeinthecircadianbodyclockcyclethattheywouldnormallybeasleep.
The furthersleep isdisplaced from theoptimumpartof thecircadianbodyclockcycle, themoredifficult itbecomesforcrewmemberstogetadequatesleep(i.e.,themorelikelytheyaretoexperiencesleeprestriction).Forexample,crewmembersflyingdomesticnightcargooperationsaretypicallyondutythroughmostoftheoptimum time forsleep in thecircadianbodyclockcycle. Thishappensbecause thecircadianbodyclock islocked on to the day/night cycle, and does not flip its orientation to promote sleep during the day whencrewmembersareflyingatnight.
Figure 2.4 summarises what happened to the circadian biological clock and sleep when the night cargocrewmembersinFigure2.3wereflyingatnightandtryingtosleepinthemorning.(Recallthattheyhadtheircoretemperaturemonitoredcontinuouslyacross8daytrippatterns,andkeptsleepanddutydairies.)
Thecoretemperaturerhythmissummarizedasasimple(continuous)curve.LookingbackatFigure2.3,whenthesecrewmemberswereoffdutyandsleepingatnight,theaveragetimeofthetemperatureminimumwas05:20. In Figure 2.4, when they were working through the night, the average time of the temperatureminimumshiftedto08:08(adelayof2hours48minutes).Thisconfirmsthatthecircadianbodyclockdidnotadaptfullytonightduty(whichwouldhaverequiredashiftofabout12hours).
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Figure2.4:Thecircadianbodyclockandsleepafternightduty
Theincompleteadaptationofthecircadianclockforcedcrewmemberstosleepinadifferentpartofthecircadianbodyclockcycleafternightduty.
Athomebeforethetrip(Figure2.3),theywenttosleepabout5hoursbeforethetemperatureminimumandwokeupabout3hoursafterthetemperatureminimum.
Afternightduty(Figure2.4),theywenttosleepclosetothecircadiantemperatureminimumandwokeupabout6hourslater.Theaveragetimeofwakingupaftermorningsleepperiodswas14:13.Thepredictedtimeoftheinternalalarmclock(6hoursafterthetemperatureminimum)was14:08.Crewmemberswerenotaskedwhatwokethemup,buttheyratedthemselvesasnotfeelingwellrestedaftertheserestrictedmorningsleepepisodes.
Another consequence of the incomplete adaptation of the circadian body clock to night duty was thatcrewmemberswereoftenoperatingthelastflightofthenightintheWindowofCircadianLow(WOCL)whentheywouldbeexpectedtobesleepyandhavingtomakeadditionalefforttomaintaintheirperformance.Nofatiguerelated incidents were observed on these flights (all crews were accompanied by a flight deckobserver).However,allflightswereroutine,i.e.,therewerenooperationaleventsthattestedthecapacityofthesecrewmemberstorespondtononroutinesituations.
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2.3.5JetLagFlyingacrosstimezonesexposesthecircadianbodyclocktosuddenshiftsintheday/nightcycle.Becauseofitssensitivitytolightand(toalesserextent)socialtimecues,thecircadianbodyclockwilleventuallyadapttoanewtimezone.Studieswithparticipantsflownaspassengershave identifiedanumberof factorsthataffecttherateofadaptationtoanewtimezone.Thesefactorsincludethefollowing.
Thenumberoftimezonescrossed adaptationgenerallytakeslongerwhenmoretimezonesarecrossed. Thedirectionoftravel adaptationisusuallyfasterafterwestwardtravelthanaftereastwardtravelacross
thesamenumberoftimezones.
Thisprobably
reflects
the
fact
that
most
people
have
acircadian
body
clock
that
has
an
innate
cycle slightly longer than 24 hours, which makes it easier to lengthen the cycle to adapt to awestwardshift(aphasedelay).
Aftereastwardflightsacross6ormoretimezones,thecircadianbodyclockmayadaptbyshiftingintheoppositedirection,forexampleshifting18timezoneswestratherthan6timezoneseast.When this happens some rhythms shift eastward and others westward (known asresynchronizationbypartition)andadaptationcanbeparticularlyslow.
Rhythmsindifferentfunctionscanadaptatdifferentrates,dependingonhowstronglytheyareinfluencedbythecircadianbodyclock.
OperationalNote:MitigationStrategiesforNightDuty
Night duty forces crewmembers to sleep later than normal in their circadian body clockcycle. This means that they have a limited amount of time to sleep before the circadianbody clock wakes them up. Consequently, they need to get to sleep as soon as possible
aftercomingoffduty.
Getting off duty earlier increases the time available for sleep in the morning, before thecircadianbodyclockmakesitdifficultforcrewmemberstostayasleep.
Napping before going on duty is beneficial to help maintain alertness and performancethroughtotheendofthenight
Nappingduringthedutyperiod(forexample,onthegroundwhileaircraftarebeingloadedandunloaded)isbeneficialtohelpmaintainalertnessandperformancethroughtotheendof the night. The napping opportunity should be limited to 4045 minutes, with an
additional1015minutesallowedtoensurethatsleepinertia(ifany)hasdissipated.
Insomeoperations, itmaybepossible toschedulea longersleepopportunityduring thenight, for example during loading and unloading of freight, or during continuous dutyovernightperiods.Providingasleepingroomawayfromtheaircraftandprotectedtimetosleepwouldincreasetheamountofsleepthatcrewmembersareabletoobtain.Onceagain1015minutesallowed,toensurethatsleepinertia(ifany)hasdissipated.
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Thismeansthatduringadaptationtothenewtimezone,rhythmsindifferentbodyfunctionscanbedisturbedfromtheirusualrelationshipstooneanother.
Adaptationisfasterwhenthecircadianbodyclockismoreexposedtothetimecuesthatitneedstolockonto inthenewtimezone.Thisrelatestotheextenttowhichpeopleadoptthepatternofsleep,eatingetc,inthenewtimezoneandtheamountoftimetheyspendoutdoorsinthefirstfewdays.
Beginningatripwithasleepdebtseemstoincreasethedurationandseverityofjetlagsymptoms.
Duringtheperiodofadaptationtothenewtimezone,commonsymptomsincludewantingtoeatandsleepattimesthatareoutofstepwiththelocalroutine,problemswithdigestion,degradedperformanceon mentalandphysicaltasks,andmoodchanges.
Thesituationforlonghaulandultralongrangeflightcrewisdifferenttothatforthepassengerwhoplanstospend longenoughat thedestination toadapt fullyto localtime.Typically, layovers ineachdestination lastonly 12 days, after which crewmembers are asked to operate a return flight or additional flights in thedestination region, followedby thereturn flight(s) to theircityoforigin.Thismeans thatthecircadianbodyclockdoesnothaveenoughtimetoadapttoanyofthedestinationtimezones.Inaddition,thecombinationofa longduty day followedby12day layoversgivesaduty/rest cycle thatdoesnot followa regular24hourpattern,sothecircadianbodyclockcannotlockontotheduty/restcycle.
Relatively few studies have tracked the circadian body clock across commercial longhaul trip patterns andnonehave tracked itacrossULRoperations.Figure 2.5depictsdata fromoneNASAstudyconducted in themid1980sonB747200/300operations (3personcrewsconsistingofapilot incommand , firstofficer,andflightengineer)15.Similartrippatternsarestillbeingflownbysomeoperatorsbutwithanadditionalpilot,nota flightengineer.Participantshad theircorebody temperaturemonitoredcontinuously andkeptsleepanddutydiariesbefore,during,andafterthistrip,whichincluded4transPacificflightsplusoneroundtripwithinAsia (NRTSINNRT). The dots on the graph indicate the time of the temperature minimum (averaged for 6crewmembersperday).
15Gander,P.H.,Gregory,K.B.,Miller,D.L.,Rosekind,M.R.,Connell,L.J.,andGraeber,R.C.(1998)FlightcrewfatigueV:long
haulairtransportoperations.Aviation,Space,andEnvironmentalMedicine69:B37B48
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Figure2.5:StudytrackingthecircadianbodyclockacrossmultipletransPacificflights
Bytheendofthistrippattern,thetemperatureminimumhaddelayedbyabout4.5hours,givinganaveragedriftrateofabout30minutesper24hours (oranaveragecycle lengthofthecircadianbodyclockofabout24.5hours).Thedriftpresumablywastheresultofthefactthatthecircadianbodyclockdidnothaveany24hourtimecuestolockonto,withthenon24hrduty/restcycleandeverylayoverinadifferenttimezone.
One consequence was that the temperature minimum (corresponding to the Window of Circadian Low orWOCL) sometimes occurred in flight, for example on the last flight from NRT to SFO. At these times,crewmembers would be expected to be sleepy and having to make additional effort to maintain theirperformance.Thiswouldbean idealtimetotakean inflightnap (crewmembersdidnothave inflightsleepopportunitiesonthistrip).
Another consequence was that when crewmembers returned home, their circadian body clocks were onaverage4.5hoursdelayedwithrespecttolocaltimeandtookseveraldaystoreadapt.
LayoverSleep
Patterns
on
Long
Haul
and
ULR
Trips
The fact that long haul and ULR crewmembers seldom stay long enough in any destination time zone tobecomeadaptedtolocaltimehaseffectsontheirlayoversleep.Often,crewmemberssplittheirsleep,havingone sleep period on local night and another corresponding to local night in their home time zone, whichoverlapsthepreferredpartofthecircadianbodyclockcycleforsleep(atleastforthefirst2448hoursinanewtimezone).
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Anotherfactoraffecting layoversleep,particularly forunaugmentedcrewswhodonothavetheopportunityfor inflight sleep, is that long haul duty days are often associated with extended periods of waking. Forexample, in a series of long haul trips studied by the NASA Fatigue Program the average period of wakingassociatedwithadutydaywas20.6hours(theaveragelengthofadutyperiodwas9.8hours)13. Acrosstheselongperiodsofwaking,thehomeostaticpressureforsleepbuildssothatcrewmemberstendtosleep,atleastforashorttime,soonafterarrivalatthedestinationlayoverhotel.Forexample,thisisacommonpatternaftereastward night flights across multiple time zones. A short sleep is taken soon after arrival, during the local
afternoon,andthenthemainsleepperiodisthentakenduringlocalnight.
FRMStrainingforlonghaulandULRcrewmembersneedstoincludediscussionoftheeffectsoftransmeridianflightsonthecircadianbodyclockandsleep.Onewaytoreducethecomplexityofthismaterialistodevelopspecificguidanceforsleepandtheuseofpersonalfatiguemitigationstrategiesondifferentroutes.
OperationalNote:EffectsofDifferentTypesofLongHaulTripPatterns
ontheCircadianBodyClock
Relativelyfewstudieshavetrackedthecircadianbodyclockacrosslonghaultrippatterns,andmanyareover20yearsold.Theavailablestudiessuggestthatdifferenttypesoftrippatternsaffectthecircadianbodyclockindifferentways.
Sequencesofbacktobacktransmeridian flights (separatedby24hour layovers)thatdonot return to the domicile time zone for long periods of time (such as the patternillustratedinFigure2.5)tendtocausethecircadianbodyclocktodriftonitsinnatecycle,whichistypicallyslightlylongerthan24hours.Thisisprobablybecausethesetripscontainnoregular24hourpatterntowhichthecircadianbodyclockcansynchronize.Whentheyarrivebackintheirhometimezone,crewmembersneedadditionaldaystoreadapttolocaltime.
Sequences of outandback transmeridan flights (separated by 24 hour layovers) thatreturn to the home time zone on alternate layovers seem to enable the circadian body
clocktoremainsynchronizedtothehometimezone.Forexample,atrippatternstudiedbytheNASAFatigueProgram involvedthreebacktobackreturn flightsbetweentheUSWest Coast and London (6 flights in total) with 24hour layovers between each flight.Returning to their home time zone on every second layover appeared to keepcrewmembers circadian body clocks (monitored by the core temperature rhythm)synchronizedtoWestCoasttime.Asaresult,crewmembersobtainedrelativelygoodsleepontheWestCoastlayoversanddidnotneedadditionaldaystoreadapttoWestCoasttimeattheendofthetrip.
Thereissomeevidencethatwhencrewmembersstaylongerinthedestinationregion,forexampledoingseveraldaysoflocalflyingwithminimaltimezonechangesbeforeflyingthe
longhaul
trip
home,
their
circadian
body
clocks
begin
to
adapt
to
the
destination
time
zone.Thismay improve layoversleep.Ontheotherhand,whentheyarriveback intheirhometimezone,theyneedadditionaldaystoreadapttolocaltime.
Thescarcityofdataonwhathappenstothecircadianbodyclockacrossdifferentlonghaultrippatterns is one reason most current biomathematical models do not have a validatedapproach for simulating what happens to the circadian clock across sequences of transmeridianflights(seeChapterFour).
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2.4SummaryofEssentialScienceforFRMSDiscoveriesinsleepscienceandcircadianrhythmsprovideastrongscientificbasisforFRMS.Thesciencedoesnotaddresseverydetailedoperationalquestionanditneverwill.Inotherwords,therewillalwaysbeaneedtocombineoperationalexperienceandscientificknowledgetocomeupwithworkablecontrolsandmitigationstomanagefatigueriskinanFRMS.
ThescientificbasisforFRMScanbecontinuouslyimprovedifdatathatareroutinelycollectedaspartofFRMprocesses(ChapterFour)andFRMSAssuranceprocesses(ChapterFive)canbesharedinappropriatewaysinthepublicdomain.
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OperationalNote:KeyFactsAboutSleep
Sleep isvitalforrecoveryfromfatigue.Twoaspectsofsleepare importanttheamountofsleepandthequalityofsleep.
AmountofSleep Sleeprestrictioniscommoninflightoperations.
Not
getting
enough
sleep
leads
to:
feeling
sleepier,
difficulty
staying
alert,
getting
irritable,
slower
reactions,poorercoordination,slowerthinking,gettingfixatedonpartofaproblemand losingthebigpicture(lossofsituationawareness), lesscreativeproblemsolving,andreducedmemoryconsolidation(impairedlearning).
Theeffectsofrestrictedsleepaccumulate: the rateofaccumulationof fatigue is related to the rateof sleep loss (lesssleepperday=more
rapidaccumulationoffatigue); sleep pressure eventually becomes uncontrollable, which results in unintentional sleep
(microsleepsorunintendednaps). Losthoursofsleepdonotneedtoberecoveredhourforhour. Atleasttwoconsecutivenightsofunrestrictedsleeparerequiredtorecoverfromthecumulativeeffects
ofmultiplenightsofrestrictedsleep.Unrestrictedsleepmeansbeingfreetofallasleepwhentiredandwakeupspontaneously,withsleepoccurringattheappropriatetimeinthecycleofthecircadianbody
clock.Insomecases,thisrecoveryperiodcanbebuilt intoschedules(forexamplewithshortdaytimedutyperiods).
Controlled napping can temporarily relieve the symptoms of sleep loss. It is a valuable personalmitigationstrategy,forexamplepriortoanightdutyperiodoronlonghaulflights. ANASAstudyof flightdecknappingshowed improvedalertnessattheendofunaugmented long
haulflights(89hrs)whenflightcrewmembersweregivena40minnapopportunityintheirflightdeckseat.
QualityofSleep Goodqualitysleep involvesregularcyclesthroughtwodifferenttypesofsleepRapidEyeMovement
sleep(REMsleep)andnonREMsleep.AfullnonREM/REMsleepcycletakesroughly90minutes. Sleepthatisfragmentedbymultipleawakenings,orarousalsinto lighterstagesofsleep,breaksupthe
nonREM/REMcycleandislessrestorativethancontinuoussleep. Sleepinonboardcrewrestfacilitiesislighterandmorefragmentedthansleepinhotelsorathome.
Thisdoesnotappeartobeaneffectofaltitude. Both flight decknaps and inflight sleep in crew rest facilities containvery littledeep nonREM sleep
(known as slowwave sleep), so sleep inertia is less likely after inflight sleep than is predicted bylaboratorystudies.
Twomainphysiologicalprocessesinteracttoregulatesleep The homeostatic sleep process is evident in the pressure for slowwave sleep that builds up across
wakinganddischargesacrosssleep.
The circadian body clock regulates the timing of REM sleep and dictates the preference for sleep atnight.
The
interaction
between
the
homeostatic
pressure
for
sleep
and
the
circadian
body
clock
results
in
two
timesofpeaksleepinessin24hours: a peak in the early afternoon (the afternoon nap window) that occurs around 35 pm for most
people;and apeakintheearlyhoursofthemorning(thewindowofcircadianloworWOCL)thatoccursaround
35amformostpeople.Note:thesetwoprocessesarethemaincomponentsinmostofthebiomathematicalmodelsthatareusedtopredictcrewmemberfatiguelevels(seeChapterFour).
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OperationalNote:KeyFactsAboutTheCircadianBodyClock
Thecircadianbodyclockisapacemakerinthebrainthatissensitivetolightthroughaspecializedinputpathwayfromtheeyes(separatefromvision).
Thecircadianbiologicalclockgeneratesaninnatebiologicaldaythatisslightlylongerthan24hoursformostpeople.Itssensitivitytolightenablesittostayinstepwiththe24hourday/nightcycle.
Almost
every
aspect
of
human
functioning
(physical
or
mental)
undergoes
daily
cycles
that
are
influencedbythecircadianbodyclock. Thedailyminimumincorebodytemperaturecorrespondstothetimeinthecircadianbodyclockcycle
whenpeoplefeelmostsleepyandareleastabletoperformmentalandphysicaltasks.ThisissometimescalledtheWindowofCircadianLow(WOCL)anditisatimeofhighriskforfatiguerelatederror.
ShiftWork
Shiftworkcanbedefinedasanydutypatternthatrequiresacrewmembertobeawakeduringthetimeinthecircadianbodyclockcyclethattheywouldnormallybeasleep.
Theabilityofthecircadianclocktolockontothe24hourday/nightcyclemakesitresistadaptationtoanypatternotherthansleepatnight.
Thefactthatthecircadianbodyclockdoesnotadaptfullytoalteredsleep/wakepatternshastwomainconsequences; dutydays thatoverlapcrewmembersusual sleep times (particularlyallnightoperations) tend to
causesleeprestriction;and crewmemberswhoareworkingthroughthewindowofcircadianlow(WOCL)canbeexpectedtobe
sleepyandhavetomakeadditionalefforttomaintaintheirperformance. Thefurthersleepisdisplacedfromtheoptimumpartofthecircadianbodyclockcycle,themoredifficult
itbecomesforcrewmemberstogetadequatesleep. Inscheduling,thefrequencyofrecoverybreaks(atleast2consecutivenightsofunrestrictedsleep)
needstoreflecttherateofaccumulationofsleepdebt.
JetLag Flying across time zones exposes the circadian body clock to sudden shifts in the day/night cycle.
Becauseof itssensitivityto lightand(toa lesserextent)socialtimecues,thecircadianbodyclockwill
eventuallyadapttoanewtimezone. Therateofadaptationdependsonthenumberoftimezonescrossed,thedirectionoftravel(fasterafter
westwardflights)andtheextenttowhichthecircadianbodyclockisexposedtothe24hourcuesinthenewtimezone(outdoorlight,sleepingandeatingonlocaltime,etc).
Layoversof2448hoursarenotlongenoughtoallowthecircadianbodyclocktoadapttolocaltime. Differenttypesoflonghaultrippatternsaffectthecircadianbodyclockindifferentways.
Sequencesofbacktobacktransmeridian flightsthatdonotreturnto thedomiciletimezone forlongperiodsoftimetendtocausethecircadianbodyclocktodriftonitsinnatecycle.Onreturntothehometimezone,additionaldaysareneededtoreadapttolocaltime.
Sequences of outandback transmeridan flights that return to the home time zone on alternatelayoversseemtoenablethecircadianbodyclocktoremainsynchronizedtothehometimezone.
Ontripsthatincludelongerperiodsinthedestinationregion,forexampleseveraldaysoflocalflying
before
the
return
flight
home,
the
circadian
body
clock
begins
to
adapt
to
the
destination
time
zone.
Thismay improve layoversleep.On theotherhand,on return tothehome timezone,additionaldaysareneededtoreadapttolocaltime.
On long haul layovers, sleep is affected by competition between physiological processes (thehomeostaticsleepdriveandthecircadianbiologicalclock)andapreferenceforsleepingduringthelocalnight.
Routespecific recommendations for personal fatigue mitigation strategies may be useful in FRMStrainingforlonghaulandULRcrewmembers.
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OperationalNote:HowMuchSleepin24hoursisEnough?
This common question is usually aimed at trying to get a magic number for the minimumamount of sleep that a crewmember needs, or the minimum rest period that needs to be
scheduled. From a sleep science perspecti
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