2.0 Introduction................................................................................................................... 2.1

2.1 Objectives...................................................................................................................... 2.1

2.2 “SuccessfulVersusUnsuccessful”Go/NoGoDecisions.............................................. 2.12.2.1 AnIn-servicePerspectiveOnGo/NoGoDecisions................................................. 2.22.2.2 “Successful”Go/NoGoDecisions........................................................................... 2.32.2.3 RTOOverrunAccidentsandIncidents..................................................................... 2.42.2.4 Statistics.................................................................................................................... 2.52.2.5 LessonsLearned....................................................................................................... 2.6

2.3 DecisionsandProcedures—What Every Pilot Should Know....................................... 2.72.3.1 TheTakeoffRules —The Source of the Data........................................................... 2.82.3.1.1 The“FAR”TakeoffFieldLength........................................................................ 2.82.3.1.2 V1 Speed Defined.................................................................................................... 2.102.3.1.3 Balanced Field Defined..................................................................................... 2.112.3.1.4 (NotUsed)......................................................................................................... 2.122.3.2 Transition to the Stopping Configuration............................................................... 2.122.3.2.1 FlightTestTransitions....................................................................................... 2.122.3.2.2 AirplaneFlightManualTransitionTimes......................................................... 2.122.3.3 Comparingthe“Stop”and“Go”Margins.............................................................. 2.142.3.3.1 The“Stop”Margins........................................................................................... 2.152.3.3.2 The“Go”Option............................................................................................... 2.162.3.4 OperationalTakeoffCalculations........................................................................... 2.182.3.4.1 TheFieldLengthLimitWeight......................................................................... 2.182.3.4.2 ActualWeightLessThanLimitWeight............................................................ 2.192.3.5 FactorsthatAffectTakeoffandRTOPerformance................................................. 2.192.3.5.1 RunwaySurfaceCondition............................................................................... 2.202.3.5.1.1 Hydroplaning............................................................................................... 2.212.3.5.1.2 TheFinalStop.............................................................................................. 2.222.3.5.2 AtmosphericConditions.................................................................................... 2.222.3.5.3 Airplane Configuration...................................................................................... 2.232.3.5.3.1 Flaps.............................................................................................................. 2.232.3.5.3.2 EngineBleedAir.......................................................................................... 2.232.3.5.3.3 MissingorInoperativeEquipment.............................................................. 2.23

Pilot Guide to Takeoff SafetyTable of Contents

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2

2.i

2.3.5.3.4 Wheels,Tires,andBrakes............................................................................ 2.252.3.5.3.5 WornBrakes................................................................................................. 2.272.3.5.3.6 ResidualBrakeEnergy................................................................................. 2.282.3.5.3.7 SpeedbrakeEffectonWheelBraking........................................................... 2.282.3.5.3.8 CarbonandSteelBrakeDifferences............................................................ 2.302.3.5.3.9 HighBrakeEnergyRTOs............................................................................. 2.312.3.5.4 ReverseThrustEffects...................................................................................... 2.322.3.5.5 RunwayParameters........................................................................................... 2.332.3.5.6 (NotUsed)......................................................................................................... 2.342.3.5.7 TakeoffsUsingReducedThrust........................................................................ 2.342.3.5.8 TheTakeoffDatathePilotSees........................................................................ 2.342.3.6 IncreasingtheRTOSafetyMargins........................................................................ 2.352.3.6.1 RunwaySurfaceCondition............................................................................... 2.352.3.6.2 FlapSelection.................................................................................................... 2.352.3.6.3 RunwayLineup................................................................................................. 2.362.3.6.4 SettingTakeoffThrust....................................................................................... 2.362.3.6.5 ManualBrakingTechniques.............................................................................. 2.372.3.6.6 AntiskidInoperativeBrakingTechniques......................................................... 2.382.3.6.7 RTOAutobrakes................................................................................................ 2.382.3.6.8 (NotUsed)......................................................................................................... 2.392.3.6.9 TheV1Call........................................................................................................ 2.392.3.6.10 CrewPreparedness............................................................................................ 2.40

2.4 CrewResourceManagement...................................................................................... 2.402.4.1 CRMandtheRTO................................................................................................. 2.402.4.2 The Takeoff Briefing............................................................................................... 2.402.4.3 Callouts................................................................................................................... 2.412.4.4 TheUseofAllCrewMembers............................................................................... 2.412.4.5 Summary................................................................................................................. 2.42

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SECTION 2

2.0 Introduction

The Pilot Guide to Takeoff Safety is onepartoftheTakeoff Safety Training Aid.TheotherpartsincludetheTakeoffSafetyOverviewforManagement (Section 1), Example TakeoffSafetyTrainingProgram(Section3),TakeoffSafetyBackgroundData (Section4),andanoptionalvideo.ThesubsectionnumberingusedinSections2and4areidenticaltofacilitatecrossreferencing.ThosesubsectionsnotusedinSection2arenoted“notused”.

Thegoalof the trainingaid is to reduce thenumberofRTOrelatedaccidentsbyimprovingthe pilot’s decision making and associatedproceduralaccomplishmentthroughincreasedknowledge and awareness of the factorsaffectingthesuccessfuloutcomeofthe“Go/NoGo”decision.

T he educat iona l mate r ia l and t herecommendations provided in the Takeoff Safety Training Aidweredevelopedthroughanextensivereviewprocesstoachieveconsensusoftheairtransportindustry.

2 .1 Objectives

The objective of the Pilot Guide to TakeoffSafetyistosummarizeandcommunicatekeyRTO related information relevant to flight crews.It isintendedtobeprovidedtopilotsduringacademic trainingand tobe retainedforfutureuse.

2.2 “Successful Versus Unsuccessful” Go/No Go Decisions

Any Go/No Go decision can be considered“successful”ifitdoesnotresult ininjuryorairplanedamage.However,justbecauseitwas“successful” by this definition, it does not mean theactionwasthe“best”thatcouldhavebeentaken.ThepurposeofthissectionistopointoutsomeofthelessonsthathavebeenlearnedthroughtheRTOexperiencesofotherairlinecrewssincethe1950s,andtorecommendwaysofavoidingsimilarexperiencesbythepilotsoftoday’s airline fleet.

Pilot Guide to Takeoff Safety

Takeoffs, RTOs, and Overruns

Through 2003 Typical Recent Year

Takeoffs 430,000,000 18,000,000

RTOs (est.)

RTO Overrun Accidents/Incidents

143,000 6,000

97 4*

• 1 RTO per 3,000 takeoffs

• 1 RTO overrun accident/incident per 4,500,000 takeoffs

*Accidents/incidents that would occur if historical rates continue.

Figure 1Takeoffs, RTOs, and Overrun Statistics

2.1

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2.2.1 An In-service Perspective On Go/No Go Decisions

Modern jet transport services began in theearly 1950s and significantly increased later thatdecadeafter introductionof theBoeing707 and the Douglas DC-8. As shown inFigure 1, the western built jet transport fleet has accumulated approximately 430 milliontakeoffsbytheendof2003.Recentlytherehavebeennearly18milliontakeoffsinatypicalyear.That’sapproximately34takeoffseveryminute,everyday!

Since no comprehensive fleet-wide records are available, it is difficult to identify the total numberofRTOsthathaveoccurredthroughoutthe jet era. However, based on those eventswhichhavebeendocumented,ourbestestimateisthatonein3,000takeoffattemptsendswithanRTO.Atthisrate,therewillbenearly6000RTOsduringatypicalyear.Thatmeansthatevery day, 16 flight crews will perform an RTO. Statistically,attherateofoneRTOper3000takeoffs, a pilot who flies short haul routes and makes80departurespermonth,willexperienceoneRTOevery threeyears.At theoppositeextreme,thelonghaulpilotmakingonlyeightdeparturespermonthwillbefacedwithonlyoneRTOevery30years.

TheprobabilitythatapilotwilleverberequiredtoperformanRTOfromhighspeedisevenless,asisshowninFigure2.

Availabledataindicatesthatover75%ofallRTOsareinitiatedatspeedsof80knotsorless.TheseRTOsalmostneverresultinanaccident.Inherently,lowspeedRTOsaresaferandlessdemandingthanhighspeedRTOs.Attheotherextreme,about2%oftheRTOsareinitiatedatspeedsabove120knots.Overrunaccidentsandincidentsthatoccurprincipallystemfromthesehighspeedevents.

What should all these statistics tell a pilot?First,RTOsarenotaverycommonevent.Thisspeakswell of equipment reliability and thepreparationthatgoesintooperatingjettransportairplanes.Bothare,nodoubt,dueinlargepartto the certification and operational standards developedbytheaviationcommunityovermanyyearsofoperation.Second,andmoreimportant,the infrequency of RTO events may lead tocomplacencyaboutmaintainingsharpdecisionmakingskillsandproceduraleffectiveness.Inspiteoftheequipmentreliability,every pilot must be prepared to make the correct Go/No Go decision on every takeoff-just in case.

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2.2

Figure 2Distribution of RTO Initiation

Speeds

2.2.2 “Successful” Go/No Go Decisions

AswasmentionedatthebeginningofSection2.2,thereismoretoa“good”Go/NoGodecisionthanthefactthatitmaynothaveresultedinanyapparent injuryoraircraftdamage.Thefollowing examples illustrate a variety ofsituations thathavebeenencountered in thepast, some of which would fit the description ofa“good”decision,andsomewhichare,atleast,“questionable”.

Listedatthebeginningofeachofthefollowingexamples is theprimarycauseorcuewhichpromptedthecrewtorejectthetakeoff:

1.TakeoffWarningHorn:Thetakeoffwarninghornsoundedasthetakeoffrollcommenced.Thetakeoffwasrejectedat5knots.Theaircraftwastaxiedofftheactiverunwaywherethecaptaindiscoveredthestabilizertrimwassetattheaftendofthegreenband.Thestabilizerwasresetandasecondtakeoffwas completed without further difficulty.

2.TakeoffWarningHorn:Thetakeoffwasrejectedat90knotswhenthetakeoffwarninghornsounded.Thecrewfoundthespeedbrakeleverslightlyoutofthedetent.Anormaltakeoffwasmadefollowingadelayforbrakecooling.

3.EnginePowerSetting:ThethrottleswereadvancedandN1increasedtoslightlyover95%.N1eventuallystabilizedat94.8%N1.ThetargetN1fromtheFMCTakeoffPagewas96.8%N1.Thethrottles were then moved to the firewall buttheN1stayedat94.8%.ThetakeoffwasrejectedduetolowN1at80knots.

4.CompressorStall:Thetakeoffwasrejectedfrom155knotsduetoabirdstrikeandsubsequentcompressorstallonthenumberthreeengine.Mostofthetires subsequently deflated due to melted fuseplugs.

5.NoseGearShimmy:Thecrewrejected

thetakeoffafterexperiencinganoselandinggearshimmy.AirspeedatthetimewasapproximatelyVl-10knots.Allfourmaingeartiressubsequentlyblewduring the stop, and fires at the number 3 and 4 tires were extinguished by the fire department.

6.BlownTire:Thetakeoffwasrejectedat140knotsduetoablownnumber3maingeartire.Number4tireblewturningontothetaxiwaycausingthelossofbothAandBhydraulicsystemsaswellasmajor damage to flaps, spar, and spoilers.

Theseexamplesdemonstratethediversityofrejectedtakeoffcauses.AlloftheseRTOswere“successful”, but some situations came veryclose to ending differently. By contrast, thelargenumberoftakeoffsthataresuccessfullycontinuedwithindicationsofairplanesystemproblemssuchascautionlightsthatilluminateat high speed or tires that fail near V1, arerarely ever reported outside the airline’sown information system. They may resultindiversionsanddelaysbutthelandingsarenormally uneventful, and can be completedusingstandardprocedures.

This should not be construed as a blanketrecommendationto“Go,nomatterwhat.”ThegoalofthistrainingaidistoeliminateRTOaccidentsbyreducingthenumberofimproperdecisionsthataremade,andtoensurethatthecorrect procedures are accomplished whenanRTOisnecessary.Itisrecognizedthatthekindofsituationsthatoccurinlineoperationsare not always the simple problem that thepilot was exposed to in training. Inevitably,the resolution of some situations will onlybe possible through the good judgment anddiscretion of the pilot, as is exemplified in the followingtakeoffevent:

After selecting EPR mode to set takeoffthrust,therightthrustleverstuckat1.21EPR,whiletheleftthrustlevermovedto

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2.3

thetargetEPRof1.34.Thecaptaintriedtorejectthetakeoffbuttherightthrustlevercouldnotbemoved to idle.Because thelightweightaircraftwasacceleratingveryrapidly,theCaptainadvancedthethrustontheleftengineandcontinuedthetakeoff.The right engine was subsequently shutdown during the approach, and the flight wasconcludedwithanuneventfulsingleenginelanding.

Thefailurethatthiscrewexperiencedwasnotastandardtrainingscenario.NorisitincludedheretoencouragepilotstochangetheirmindinthemiddleofanRTOprocedure.Itissimplyanacknowledgmentofthekindofrealworlddecisionmakingsituationsthatpilotsface.Itisperhapsmoretypicalofthegoodjudgementsthatairlinecrewsregularlymake,buttheworldrarelyhearsabout.

2.2.3 RTO Overrun Accidents and Incidents

Theone-in-one-thousandRTOsthatbecameaccidents or serious incidents are the onesthatwemust strive toprevent.Asshown inFigure3,attheendof2003,recordsshow57in-serviceRTOoverrunaccidentsforthewesternbuilt jet transport fleet. These 57 accidents causedmorethan400fatalities.Anadditional

40 serious incidents have been identified which likelywouldhavebeenaccidentsiftherunwayoverrun areas had been less forgiving. Thefollowing are brief accounts of four actualaccidents.Theyarerealevents.Hopefully,theywillnotberepeated.

ACCIDENT: At 154 knots, four knots afterV1,thecopilot’ssidewindowopened,andthetakeoff was rejected. The aircraft overran,hittingablastfence,tearingopentheleftwingand catching fire.

ACCIDENT:Thetakeoffwasrejectedbythecaptain when the first officer had difficulty maintainingrunwaytrackingalongthe7,000footwetrunway.Initialreportsindicatethattheairplanehadslowlyacceleratedatthestartofthetakeoffrollduetoadelayinsettingtakeoffthrust. The cockpit voice recorder (CVR)readoutindicatestherewerenospeedcalloutsmade during the takeoff attempt.The rejectspeedwas5knotsaboveV1.Thetransitiontostoppingwasslowerthanexpected.Thiswasto have been the last flight in a long day for the crew.Bothpilotswererelativelyinexperiencedintheirrespectivepositions.Thecaptainhadabout140hoursasacaptaininthisairplanetype and the first officer was conducting

0

5

10

1960 1965 1970 1975 1980Year

1985 1990 1995 2000

Number of events per year

Figure 3 97 RTO overrun

accidents/incidents 1959-2003

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2.4

his first non-supervised line takeoff in this airplanetype.Theairplanewasdestroyedwhenit overran the end of the runway and brokeapartagainstpierswhichextendoff theendoftherunwayintotheriver.Thereweretwofatalities. Subsequent investigation revealedthattherudderwastrimmedfullleftpriortothetakeoffattempt.

ACCIDENT: A f lock of sea gulls wasencountered “very near V1.” The airplanereportedlyhadbegun to rotate.Thenumberone engine surged and flamed out, and the takeoff was rejected. The airplane overrantheendofthewet6,000footrunwaydespiteagoodRTOeffort.

ACCIDENT: At 120 knots, the flight crew noted theonsetofavibration.When thevibrationincreased, the captain elected to reject andassumedcontrol.Fourtoeightsecondselapsedbetween the point where the vibration was first notedandwhen theRTOwas initiated (justafterV1).Subsequentinvestigationshowedtwotireshadfailed.Themaximumspeedreachedwas158knots.Theairplaneoverrantheendofthe runway at a speed of 35 knots and finally stoppedwiththenoseinaswamp.Theairplanewasdestroyed.

Thesefourcasesaretypicalofthe97reportedaccidentsandincidents.

2.2.4 Statistics

Studies of the previously mentioned 97accidents/incidents have revealed someinterestingstatistics,asshowninFigure4:

• Fifty-five percent were initiated at speeds inexcessofV1.

• Approximatelyonethirdwerereportedashavingoccurredonrunwaysthatwerewetorcontaminatedwithsnoworice.

Both of these issues will be thoroughlydiscussedinsubsequentsections.

An additional, vitally interesting statisticthat was observed when the accidentrecords involving Go/NoGodecisionswerereviewed, was that virtually no revenuef light was found where a “Go” decisionwas made and the airplane was incapableof continuing the takeoff. Regardless of theabilitytosafelycontinuethetakeoff,aswillbeseeninSection2.3,virtuallyanytakeoffcanbe“successfully”rejected,iftherejectisinitiatedearlyenoughandisconductedproperly.ThereismoretotheGo/NoGodecisionthan“StopbeforeV1”and“GoafterV1.”ThestatisticsofthepastthreedecadesshowthatanumberofjettransportshaveexperiencedcircumstancesnearV1thatrenderedtheairplaneincapableofbeingstoppedontherunwayremaining.Italso Figure 4

Major factors in previous RTO incidents and accidents

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2.5

mustberecognizedthatcatastrophicsituationscouldoccurwhichrendertheairplaneincapableof flight.

Reasons why the 97 “unsuccessful” RTOswereinitiatedarealsoof interest.Asshownin Figure 5, approximately one-fifth were initiatedbecauseofenginefailuresorengineindicationwarnings.Theremainingseventy-nine percent were initiated for a variety ofreasonswhichincludedtirefailures,proceduralerror,malfunctionindicationorlights,noisesand vibrations, directional control difficulties andunbalancedloadingsituationswheretheairplane failed to rotate.Someof theeventscontainedmultiplefactorssuchasanRTOonacontaminated runway followinganenginefailureataspeedinexcessofV1.Thefactthatthe majority of the accidents and incidentsoccurred on airplanes that had full thrustavailable should figure heavily in future Go/No Gotraining.

2.2.5 Lessons Learned

Several lessons can be learned from theseRTO accidents. First, the crew must alwaysbepreparedtomaketheGo/NoGodecisionprior to the airplane reaching V1 speed. Aswill be shown in subsequent sections, theremaynotbeenoughrunwaylefttosuccessfullystoptheairplaneiftherejectisinitiatedafterV1.Second,inordertoeliminateunnecessaryRTOs, the crew must differentiate betweensituationsthataredetrimentaltoasafetakeoff,andthosethatarenot.Third,thecrewmustbepreparedtoactasawellcoordinatedteam.Agoodsummarizingstatementoftheselessonsis, as speed approaches V1, the successful completion of an RTO becomes increasingly more difficult.

A fourth and final lesson learned from past RTOhistoryisillustratedinFigure6.Analysisof the available data suggests that of the97

Figure 5Reasons for

initiating the RTO (97 accidents/

incident events)

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2.6

RTOaccidents and incidents, approximately82% were potentially avoidable throughappropriate operational practices. Thesepotentiallyavoidableaccidentscanbedividedintothreecategories.Roughly15%oftheRTOaccidentsofthepastweretheresultofimproperpreflight planning. Some of these instances werecausedbyloadingerrorsandothersbyincorrect preflight procedures. About 15% of theaccidentsandincidentscouldbeattributedtoincorrectpilottechniquesorproceduresinthestoppingeffort.Delayedapplicationofthebrakes,failuretodeploythespeedbrakes,andthefailuretomakeamaximumeffortstopuntillateintheRTOwerethechiefcharacteristicsofthiscategory.

Reviewofthedatafromthe97RTOaccidentsandincidentssuggeststhat inapproximately52%oftheevents,theairplanewascapableofcontinuingthetakeoffandeitherlandingatthedepartureairportordivertingtoanalternate.Inotherwords,thedecisiontorejectthetakeoffappears to have been “improper.” It is notpossible,however,topredictwithtotalcertaintywhatwouldhavehappenedineveryeventifthetakeoffhadbeencontinued.Norisitpossiblefortheanalystoftheaccidentdatatovisualizetheeventsleadinguptoaparticularaccident“throughtheeyesofthecrew”,includingalltheotherfactorsthatwerevyingfortheirattentionat the moment when the “proper” decisioncould have been made. It is not very difficult to imagineasetofcircumstanceswhere theonlylogicalthingforthepilottodoistorejectthe takeoff. Encountering a large flock of birds

atrotationspeed,whichthenproduceslossofthrustonbothenginesofatwoengineairplane,isaclearexample.

Althoughtheseareallvalidpoints,debatingthem here will not move us any closer tothe goal of reducing the number of RTOaccidents.Severalindustrygroupshaverecentlystudied this problem. Their conclusions andrecommendationsagreesurprisinglywell.Theareas identified as most in need of attention are decision making and proficiency in correctly performingtheappropriateprocedures.Theseare the same areas highlighted in Figure 6.It would appear then, that an opportunityexists to significantly reduce the number of RTOaccidentsinthefuturebyattemptingtoimprovethepilots’decisionmakingcapabilityandprocedureaccomplishmentthroughbettertraining.

2.3 Decisions and Procedures— What Every Pilot Should Know

TherearemanythingsthatmayultimatelyaffecttheoutcomeofaGo/NoGodecision.ThegoaloftheTakeoffSafetyTrainingAidistoreducethenumberofRTOrelatedaccidentsandincidentsbyimprovingthepilot’sdecisionmakingandassociatedprocedureaccomplishmentthroughincreased knowledge and awareness of therelated factors. This section discusses therules that define takeoff performance limit weightsandthemargins thatexistwhentheactual takeoff weight of the airplane is less

Figure 682% of the RTO accidents and incidents were avoidable

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2.7

thanthelimitweight.Theeffectsofrunwaysurfacecondition,atmosphericconditions,andairplane configuration variables on Go/No Go performancearediscussed,aswellaswhatthepilotcandotomakethebestuseofanyexcessavailablerunway.

Although the information contained in thissection has been reviewed by many majorairframe manufacturers and airlines, theincorporationofanyoftherecommendationsmadeinthissectionissubjecttotheapprovalofeachoperator’smanagement.

2.3.1 The Takeoff Rules — The Source of the Data

It is important that all pilots understand thetakeoff field length/weight limit rules and the marginstheserulesprovide.Misunderstandingtherulesandtheirapplicationtotheoperationalsituation could contribute to an incorrectGo/NoGodecision.

TheU.S.FederalAviationRegulations(FARs)have continually been refined so that the details of the rules that are applied to one airplanemodel may differ from another. However,thesedifferencesareminorandhavenoeffecton the basic actions required of the flight crewduringthetakeoff.Ingeneral,itismoreimportantforthecrewtounderstandthebasicprinciplesratherthanthetechnicalvariationsin certification policies.

2.3.1.1 The “FAR” Takeoff Field Length

The“FAR”TakeoffFieldLengthdeterminedfrom the FAA Approved Airplane FlightManual(AFM)considersthemostlimitingofeachofthefollowingthreecriteria:

1)All-EngineGoDistance:115%oftheactualdistancerequiredtoaccelerate,liftoffandreachapoint35feetabovetherunwaywithallenginesoperating(Figure7).

2)Engine-OutAccelerate-GoDistance:Thedistancerequiredtoacceleratewithallenginesoperating,haveoneenginefailatVEFatleastonesecondbeforeV1,continuethetakeoff,liftoffandreachapoint35feetabovetherunwaysurfaceatV2speed(Figure8).

3)Accelerate-StopDistance:Thedistancerequiredtoacceleratewithallenginesoperating,haveanenginefailureorothereventatVEVENTatleastonesecondbeforeV1,recognizetheevent,reconfigure for stopping and bring theairplanetoastopusingmaximumwheelbrakingwiththespeedbrakesextended.ReversethrustisnotusedtodeterminetheFARaccelerate-stopdistance(Figure9),exceptforthewetrunway case for airplanes certified under FARAmendment25-92.

FAR criteria provide accountability forwind, runway slope, clearway and stopway.FAAapprovedtakeoffdataarebasedontheperformancedemonstratedonasmooth,dryrunway. Recent models certified according to FARAmendment25-92alsohaveapproveddatabasedonwet,andwetskid-resistantrunways.Separateadvisorydataforwet,ifrequired,orcontaminatedrunwayconditionsarepublishedinthemanufacturer’soperationaldocuments.Thesedocumentsareusedbymanyoperatorstoderivewetorcontaminatedrunwaytakeoffadjustments..

Other criteria define the performance weight limitsfortakeoffclimb,obstacleclearance,tirespeedsandmaximumbrakeenergycapability.Anyoftheseothercriteriacanbethelimitingfactorwhichdeterminesthemaximumdispatchweight.However,theFieldLengthLimitWeightandtheamountofrunwayremainingatV1willbe theprimary focusofourdiscussionheresincetheymoredirectlyrelate topreventingRTOoverruns.

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2.9

Figure 7All-engine go distance

Figure 8Engine-out accelerate-go distance

Figure 9Accelerate-stop distance

2.3.1.2 V1 Speed Defined

V1

Whatistheproperoperationalmeaningofthekeyparameter“V1speed”withregardtotheGo/NoGocriteria?Thisisnotsuchaneasyquestionsincetheterm“V1speed”hasbeenredefined several times since commercial jet operationsbeganmorethan30yearsagoandthereispossibleambiguityintheinterpretationof the words used to define V1.

Paragraph 25.107 of the FAA Regulationsdefines the relationship of the takeoff speeds published in the Airplane Flight Manual, tovarious speeds determined in the certification testingoftheairplane.Forourpurposeshere,the most important statement within this“official” definition is that V1isdeterminedfrom“...the pilot’s initiation of the first action to stop the airplane during the accelerate-stop tests.”

OnecommonandmisleadingwaytothinkofV1istosay“V1isthedecisionspeed.”ThisismisleadingbecauseV1isnotthepointtobeginmakingtheoperationalGo/NoGodecision.The decision must have been made by the time the airplane reaches V1orthepilotwillnothaveinitiatedtheRTOprocedureatV1.Therefore,by definition, the airplane will be traveling at aspeedhigherthanV1whenstoppingaction

is initiated, and if the airplane is at a FieldLengthLimitWeight,anoverrunisvirtuallyassured.

Anothercommonlyheldmisconception:“V1istheenginefailurerecognitionspeed”,suggeststhatthedecisiontorejectthetakeofffollowingenginefailurerecognitionmaybeginaslateasV1.Again,theairplanewillhaveacceleratedtoaspeedhigherthanVIbeforestoppingactionisinitiated.

The certified accelerate-stop distance calculation isbasedonanenginefailureatleastonesecondprior to V1. This standard time allowance1has been established to allow the line pilottorecognizeanenginefailureandbeginthesubsequentsequenceofstoppingactions.

InanoperationalFieldLengthLimitedcontext,the correct definition of V1 consists of twoseparateconcepts:

First,withrespecttothe“NoGo”criteria,V1 is the maximum speed at which the rejected takeoff maneuver can be initiated and the airplane stopped within the remaining field length under the conditions and procedures defined

1ThetimeintervalbetweenVEFandVl is the longer of the flight test demonstrated time or one second. Therefore, in determining thescheduledaccelerate-stopperformance,onesecondistheminimumtimethatwillexistbetweentheenginefailureandthefirst pilot stopping action.

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2.10

in the FAR’s. It is the latest point in the takeoff roll where a stop can be initiated.Second,withrespecttothe“Go”criteria,V1 is also the earliest point from which an engine out takeoff can be continued and the airplane attain a height of 35 feet at the end of the runway. ThisaspectofV1isdiscussedinalatersection.

TheGo/NoGodecisionmustbemadebeforereachingV1.A “No Go” decision after passing V1 will not leave sufficient runway remaining to stop if the takeoff weight is equal to the Field Length Limit Weight.Whentheairplaneactual weight is less than the Field LengthLimit Weight, it is possible to calculate theactualmaximumspeedfromwhichthetakeoffcouldbesuccessfullyrejected.However,fewoperatorsusesuchtakeoffdatapresentations.ItisthereforerecommendedthatpilotsconsiderV1tobealimitspeed:DonotattemptanRTOonce the airplane has passed V1 unless thepilot has reason to conclude the airplane isunsafe or unable to fly. This recommendation should prevail no matter what runway length appears to remain after V1.

2.3.1.3 Balanced Field Defined

The previous two sections established thegeneral relationship between the takeoffperformance regulationsandV1speed.This

sectionprovidesacloserexaminationofhowthe choiceof V1 actually affects the takeoffperformance in specific situations.

Sinceitisgenerallyeasiertochangetheweightofanairplanethanitistochangethelengthofarunway,thediscussionherewillconsidertheeffectofV1ontheallowabletakeoffweightfrom a fixed runway length.

The Continued Takeoff—After an enginefailure during the takeoff roll, the airplanemustcontinuetoaccelerateontheremainingengine(s),liftoffandreachV2speedat35feet.The later in the takeoff roll that the enginefails,theheaviertheairplanecanbeandstillgainenoughspeedtomeetthisrequirement.FortheenginefailureoccurringapproximatelyonesecondpriortoV1,therelationshipoftheallowableengine-outgotakeoffweighttoV1wouldbeasshownbythe“ContinuedTakeoff”lineinFigure10.ThehighertheV1,theheavierthetakeoffweightallowed.

TheRejectedTakeoff— Onthestopsideoftheequation,theV1/weighttradehastheoppositetrend.The lower theV1,or theearlier in thetakeoffrollthestopisinitiated,theheaviertheairplanecanbe,asindicatedbythe“RejectedTakeoff”lineinFigure10.

Thepointatwhichthe“ContinuedandRejectedTakeoff”linesintersectisofspecialinterest.Itdefines what is called a “Balanced Field Limit”

Figure 10Effect of V1 speed on takeoff weight (from a fixed runway length)

Continuedtakeoff

Rejectedtakeoff

Airplaneweight

V speed1

Incr

easi

ng

Increasing

Field limit weight

Bal

ance

d fi

eld

Lim

it V

sp

eed

1

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takeoff.Thename“BalancedField”referstothe fact that the accelerate-go performancerequired is exactly equal to (or “balances”)the accelerate-stop performance required.FromFigure10itcanalsobeseenthatatthe“Balanced Field” point, the allowable FieldLimitTakeoffWeightforthegivenrunwayisthemaximum.TheresultinguniquevalueofV1isreferredtoasthe“BalancedFieldLimitV1Speed”andtheassociatedtakeoffweightiscalled the“BalancedFieldWeightLimit.”This is the speed that is typically given to flight crewsinhandbooksorcharts,bytheonboardcomputersystems,orbydispatch.

2.3.1.4 (Not Used)

2.3.2 Transition to the Stopping Configuration

In establishing the certified accelerate-stop distance, the time required to reconfigure the airplane from the “Go” to the “Stop” modeis referred to as the “transition” segment.This action and the associated time ofaccomplishmentincludesapplyingmaximumbraking simultaneously moving the thrustlevers to idle and raising the speedbrakes.The transition time demonstrated by flight test pilots during the accelerate-stop testingisusedtoderivethetransitionsegmenttimesusedintheAFMcalculations.Therelationshipbetween the flight test demonstrated transition times and those finally used in the AFM is anotherfrequentlymisunderstoodareaofRTOperformance.

2.3.2.1 Flight Test Transitions

Several methods of certification testing that producecomparableresultshavebeenfoundtobeacceptable.Thefollowingexampleillustratestheintentofthesemethods.

During certification testing the airplane is acceleratedtoapre-selectedspeed,oneengine

is “failed”by selecting fuel cut off, and thepilot flying rejects the takeoff. In human factors circles, this is defined as a “simple task” becausethetestpilotknowsinadvancethatanRTOwillbeperformed.Exactmeasurementsof the time taken by the pilot to apply thebrakes,retardthethrustleverstoidle,andtodeploythespeedbrakesarerecorded.Detailedmeasurements of engine parameters duringspooldown are also made so that the thrustactuallybeinggeneratedcanbeaccountedforinthecalculation.

The manufacturer’s test pilots, and pilotsfrom the regulatory agency, each performseveralrejectedtakeofftestruns.Anaverageof the recorded data from at least six ofthese RTOs is then used to determine the“demonstrated” transition times. The total flight test“demonstrated”transitiontime,initialbrakeapplicationtospeedbrakesup,istypicallyonesecondor less.However this isnot the totaltransition time used to establish the certified accelerate-stop distances. The certification regulationsrequirethatadditionaltimedelays,sometimesreferredtoas“pads”,beincludedinthe calculation of certified takeoff distances.

2.3.2.2 Airplane Flight Manual Transition Times

AlthoughthelinepilotmustbepreparedforanRTOduringeverytakeoff,itisfairlylikelythattheeventorfailurepromptingtheGo/NoGodecisionwillbemuchlessclear-cutthananoutrightenginefailure.Itmaythereforebeunrealistictoexpecttheaveragelinepilottoperformthetransitioninaslittleasonesecondinanoperationalenvironment.Humanfactorsliterature describes the line pilot’s job as a“complextask”sincethepilotdoesnotknowwhenanRTOwilloccur.Inconsiderationofthis “complex task”, the flight test transition times are increased to calculate the certified accelerate-stop distances specified in the AFM. These additional time increments are not

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intended to allow extra time for making the “Go/No Go” decision after passing V1.Theirpurpose is to allow sufficient time (and distance) for“theaveragepilot”totransitionfromthetakeoffmodetothestoppingmode.

The first adjustment is made to the time required torecognizetheneedtostop.DuringtheRTOcertification flight testing, the pilot knows thathewillbedoinganRTO.Therefore,hisreaction ispredictablyquick.Toaccountforthis,aneventrecognitiontimeofatleastonesecondhasbeensetasa standard forall jettransport certifications since the late 1960s. V1 is therefore,at leastonesecondafter theevent.Duringthisrecognitiontimesegment,theairplanecontinues toacceleratewith theoperatingengine(s)continuingtoprovidefullforward thrust. If the event was an enginefailure,the“failed”enginehasbeguntospooldown,but it is still providing some forwardthrust,addingtotheairplane’sacceleration.

Overtheyears,thedetailsofestablishingthetransitiontimesegmentsafterV1havevariedslightlybuttheoverallconceptandtheresulting

transitiondistanceshaveremainedessentiallythe same. For early jet transport models, anadditionalonesecondwasaddedtoboththeflight test demonstrated throttles-to-idle time and the speedbrakes-up time, as illustratedin Figure 11. The net result is that the flight test demonstrated recognition and transitiontime of approximately one second has beenincreased for the purpose of calculating theAFMtransitiondistance.

In more recent certification programs, the AFM calculation procedure was slightly different.Anallowance equal to thedistance traveledduringtwosecondsatthespeedbrakes-upspeedwasaddedto theactual total transitiontimedemonstrated in the flight test to apply brakes, bringthethrustleverstoidleanddeploythespeedbrakes,asshowninFigure12.Toinsure“consistentandrepeatableresults”,retardationforces resulting from brake application andspeed brake deployment are not appliedduringthistwosecondallowancetime,i.e.nodecelerationcreditistaken.Thistwoseconddistance allowance simplifies the transition distancecalculationandaccomplishesthesamegoalastheindividualonesecond“pads”used

Figure 11 Early method of establishing AFM transition time

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foroldermodels.

Evenmorerecently,FARAmendments25-42and25-92haverevisedthewayinwhichthetwoseconddistanceallowanceiscalculated.Regardlessofthemethodused,theaccelerate-stopdistancecalculatedforeverytakeofffromtheAFMistypically400to600feetlongerthanthe flight test accelerate-stop distance.

Thesedifferencesbetweenthepastandpresentmethodology are not significant in so far as the operational accelerate-stop distance isconcerned.The keypoint is that the time/distance “pads” used in the AFM transition distance calculation are not intended to allow extra time to make the “No Go” decision. Rather,the“pads”provideanallowancethatassuresthepilothasadequatedistancetogettheairplaneintothefull stopping configuration.

Regardlessoftheairplanemodel,thetransition,or reconfiguring of the airplane for a rejected takeoff,demandsquickactionbythecrewto

simultaneously initiate maximum braking,retardthethrustleverstoidleandthenquicklyraisethespeedbrakes.

2.3.3 Comparing the “Stop” and “Go” Margins

WhenperformingatakeoffataFieldLengthLimitWeightdeterminedfromtheAFM,thepilotisassuredthattheairplaneperformancewill, at the minimum, conform to therequirementsoftheFARsiftheassumptionsof thecalculationsaremet.Thismeans thatfollowinganenginefailureoreventatVEVENT,thetakeoffcanberejectedatV1andtheairplanestoppedattheendoftherunway,orifthetakeoffiscontinued,aminimumheightof35feetwillbereachedovertheendoftherunway.

Thissectiondiscussestheinherentconservatismof these certified calculations, and the margins they provide beyond the required minimumperformance.

Figure 12More recent

method of establishing AFM

transition time

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2.3.3.1 The “Stop” Margins

From the preceding discussion of thecertification rules, it has been shown that at a Field Length Limit Weight condition, anRTOinitiatedatV1willresultintheairplanecomingtoastopattheendoftherunway.Thisaccelerate-stop distance calculation specifies an enginefailureoreventatVEVENT,thepilot’sinitiationoftheRTOatV1,andthecompletionofthetransitionwithinthetimeallottedintheAFM.Ifanyofthesebasicassumptionsarenotsatisfied, the actual accelerate-stop distance mayexceedtheAFMcalculateddistance,andanoverrunwillresult.

The most significant factor in these assumptions istheinitiationoftheRTOnolaterthanV1.Yetaswasnotedpreviously,inapproximately55%oftheRTOaccidentsthestopwasinitiatedafterV1.AtheavyweightsnearV1,theairplaneis typically traveling at 200 to 300 feet persecond,andacceleratingat3 to6knotspersecond. This means that a delay of only asecondortwoininitiatingtheRTOwillrequireseveralhundredfeetofadditionalrunwaytosuccessfullycompletethestop.IfthetakeoffwasataFieldLimitWeight,andthereisnoexcessrunwayavailable,theairplanewillreachthe end of the runway at a significant speed, as showninFigure13.

The horizontal axis of Figure 13 is theincrementalspeedinknotsaboveV1atwhichamaximum effortstopisinitiated.Theverticalaxisshowstheminimum speedinknotsatwhichtheairplanewouldcrosstheendoftherunway,assuming the pilot used all of the transitiontime allowed in the AFM to reconfigure the airplane to the stop configuration, and that a maximumstoppingeffortwasmaintained.ThedatainFigure13assumesanenginefailurenotlessthanonesecondpriortoV1anddoesnotincludetheuseofreversethrust.Therefore,ifthepilotperformsthetransitionmorequicklythantheAFMallottedtime,and/orusesreversethrust,thelinelabeled“MAXIMUMEFFORTSTOP”wouldbeshiftedslightlytotheright.However,basedontheRTOaccidentsofthepast,theshadedareaabovethelineshowswhatismorelikelytooccurifahighspeedRTOisinitiatedatorjustafterV1.ThisisespeciallytrueiftheRTOwasduetosomethingotherthananenginefailure,orifthestoppingcapabilityoftheairplaneisotherwisedegradedbyrunwaysurface contamination, tire failures, or poortechnique.ThedatainFigure13aretypicalofalarge,heavyjettransportandwouldberotatedslightlytotherightforthesameairplaneatalighterweight.

In the final analysis, although the certified accelerate-stopdistancecalculationsprovide

Figure 13 Overrun Speed for an RTO initiated after V1

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sufficient runway for a properly performed RTO, theavailablemarginsare fairly small.Most importantly, there are no margins toaccountforinitiationoftheRTOafterV1orextenuating circumstances such as runwaycontamination.

2.3.3.2 The “Go” Option

FARrulesalsoprescribeminimumperformancestandardsforthe“Go”situation.Withanenginefailedatthemostcriticalpointalongthetakeoffpath,theFAR“Go”criteriarequiresthattheairplanebeabletocontinuetoaccelerate,rotate,liftoffandreachV2speedatapoint35feetabovetheendoftherunway.Theairplanemustremaincontrollablethroughoutthismaneuverandmustmeet certain minimum climb requirements.These handling characteristics and climbrequirements are demonstrated many timesthroughout the certification flight test program. Whileagreatdealofattentionisfocusedontheenginefailurecase,itisimportanttokeepinmind,thatin over three quarters of all RTO accident cases, full takeoff power was available. Itislikelythateachcrewmemberhashadagood deal of practice in engine inoperativetakeoffsinpriorsimulatororairplanetraining.However,itmayhavebeendoneatrelativelylighttrainingweights.Asaresult,thecrewmayconclude that large control inputs and rapidresponsetypicalofconditionsnearminimumcontrolspeeds(Vmcg)arealwaysrequiredinordertomaintaindirectionalcontrol.However,at the V1 speeds associated with a typicalFieldLengthLimitWeight,thecontrolinputrequirementsarenoticeablylessthantheyareatlighterweights.

Also, at light gross weights, the airplane’srate of climb capability with one-engineinoperativecouldnearlyequaltheall-engineclimb performance at typical in-serviceweights, leading the crew to expect higher

performancethantheairplanewillhaveiftheactualairplaneweightisatornearthetakeoffClimbLimitWeight.Engine-outrateofclimbandaccelerationcapabilityataClimbLimitWeightmayappeartobesubstantiallylessthanthecrewanticipatesorisfamiliarwith.

Theminimumsecondsegmentclimbgradientsrequired in the regulations vary from 2.4%to3.0%dependingonthenumberofenginesinstalled. These minimum climb gradientstranslateintoaclimbrateofonly350to500feetperminuteatactualclimblimitweightsand their associatedV2 speeds, as shown inFigure 14. The takeoff weight computationsperformed prior to takeoff are required toaccount for all obstacles in the takeoff flight path. All that is required to achieve theanticipated flight path is adherence by the flight crewtotheplannedheadingsandspeedspertheir pre-departure briefing.

Consider a one-engine-inoperative casewhere the engine failure occurs earlier thanthe minimum time before V1 specified in therules.Becauseengine-outaccelerationisless than all-engine acceleration, additionaldistance is needed to accelerate to VR and,as a consequence, the liftoff point will bemovedfurtherdowntherunway.Thealtitude(or“screenheight”)achievedattheendoftherunway is somewhat reduced depending onhowmuchmorethanonesecondbeforeV1theengine failure occurs. On a field length limit runway, theheightat theendof the runwaymay be less than the 35 feet specified in the regulations.

Figure 15 graphically summarizes thisdiscussion of “Go” margins. First, let VEFbe the speed at which the Airplane FlightManualcalculationassumestheenginetofail,(a minimum of one second before reachingV1).Thehorizontal axis ofFigure15 showsthe number of knots prior to VEF that the

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engineactuallyfailsinsteadofthetime,andthe vertical axis gives the “screen height”achievedattheendoftherunway.Atypicalrangeofaccelerationforjettransportsis3to6knotspersecond,sotheshadedareashowstherangeinscreenheightthatmightoccuriftheengineactuallyfailed“onesecondearly”,orapproximatelytwosecondspriortoV1.Inotherwords,a“Go”decisionmadewiththeengine

failureoccurringtwosecondspriortoV1willresultinascreenheightof15to30feetforaFieldLengthLimitWeighttakeoff.

Figure15alsoshowsthatthe“Go”performancemargins are strongly influenced by the number ofengines.Thisisagaintheresultofthelargerproportionofthrustlosswhenoneenginefailson the two-engine airplane compared to a

-20 -16 -12 -8 -4 00

10

20

30

40

(35)

(150)

One-engine inoperative

All engines

2-engine airplane

Height at end of runway, ft

Speed at actual engine failure relative to VEF, knots

V2 + 10 to 25 knots

V2

+8+4

Typical V1 range

One second minimum

4-engine airplane

3-engine airplane

Figure 14 “GO” perfomance at climb limit weights

Figure 15 Effect of engine failure before VEF on screen height

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threeorfour-engineairplane.Ontwo-engineairplanes,therearestillmargins,buttheyarenotaslarge,afactthatanoperatorofseveralairplanetypesmustbesuretoemphasizeintrainingandtransitionprograms.

It should also be kept in mind that the 15to 30 foot screen heights in the precedingdiscussion were based on the complete lossof thrustfromoneengine.Ifallenginesareoperating, as was the case in most of theRTOaccidentcases, theheightover theendof the Field Length Limit runway will beapproximately 150 feet and speed will beV2+10 to 25 knots, depending on airplanetype.Thisisduetothehigheraccelerationandclimbgradientprovidedwhenallenginesareoperatingandbecausetherequiredallenginetakeoffdistanceismultipliedby115%.Ifthe“failed” engine is developing partial power,the performance is somewhere in between,but definitely above the required engine-out limits.

2.3.4 Operational Takeoff Calculations

As we have seen, the certification flight testing, inaccordancewiththeappropriategovernmentregulations, determines the relationshipbetween the takeoff gross weight and therequiredrunwaylengthwhichispublishedintheAFM.ByusingthedataintheAFMitisthenpossibletodetermine,foragivencombinationofambientconditionsandairplaneweight,therequired runway length which will complywith the regulations. Operational takeoffcalculations,however,haveanadditionalandobviouslydifferent limitation.The lengthoftherunwayistheLimitFieldLengthanditisfixed, not variable.

2.3.4.1 The Field Length Limit Weight

Instead of solving for the required runwaylength, the first step in an operational takeoff calculation is to determine the maximumairplane weight which meets the rules forthe fixed runway length available. In other words,what is the limitweightatwhich theairplane:

1)Willachieve35-ftaltitudewithallenginesoperatingandamarginof15%oftheactualdistanceusedremaining;

2)Willachieve35-ftaltitudewiththecriticalenginefailedonesecondpriortoV1;

3)WillstopwithanenginefailureorothereventpriortoV1andtherejectinitiatedatV1;

…all within the existing runway lengthavailable.

Theresultofthiscalculationisthreeallowableweights.Thesethreeweightsmayormaynotbethesame,butthelowestofthethreebecomestheFieldLengthLimitWeightforthattakeoff.

Aninterestingobservationcanbemadeatthispointas towhichof thesethreecriteriawilltypically determine the Takeoff Field LimitWeightforagivenairplanetype.Two-engineairplanesloseone-halftheirtotalthrustwhenanenginefails.Asaresult,theFieldLengthLimitWeightfortwo-engineairplanesisusuallydeterminedbyoneoftheengine-outdistancecriteria.Ifitislimitedbytheaccelerate-stopdistance, therewillbe somemargin inboththeall-engineandaccelerate-godistances.Ifthe limit is theaccelerate-godistance, somemarginwouldbeavailablefortheall-enginegoandaccelerate-stopcases.

By comparison, four-engine airplanes onlyloseone-fourthoftheirtakeoffthrustwhenanenginefailssotheyarerarelylimitedbyengine-outgoperformance.TheFieldLengthLimit

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Weightforafour-engineairplaneistypicallylimitedbythe115%all-enginedistancecriteriaoroccasionallybytheaccelerate-stopcase.Asaresult,aslightmarginfrequentlyexistsintheengine-outgoandaccelerate-stopdistancesonfour-engineairplanes.

Three-engine airplanes may be limited byengine-outperformance,orforsomemodels,byamorecomplexcriterionwhereintherotationspeedVRbecomesthelimitingfactor.Sincethe regulations prohibit V1 from exceedingVR,sometri-jetsfrequentlyhaveV1=VR,anda small margin may therefore exist in theaccelerate-stopdistance.Two-engineairplanesmay occasionally be limited by this V1=VRcriterionalso.

Thepossiblecombinationsofairportpressurealtitude, temperature, wind, runway slope,clearway,andstopwayareendless.Regardlessofairplane type, theycaneasilycombine tomakeanyoneofthethreepreviouslydiscussedtakeoff field length limits apply. Flight crews havenoconvenientmethodtodeterminewhichofthethreecriteriaislimitingforaparticulartakeoff,andfromapracticalpointofview,itreally doesn’t matter. The slight differencesthat may exist are rarely significant. Most RTO overrunaccidentshaveoccurredonrunwayswheretheairplanewasnotatalimittakeoffweight. That is, the accidents occurred onrunwaysthatwerelongerthanrequiredfortheactualtakeoffweight.Combiningthishistoricalevidencewiththedemandingnatureofthehighspeedrejectedtakeoff,itwouldseemprudentthatthecrewshouldalwaysassumethetakeoffislimitedbytheaccelerate-stopcriteriawhenthetakeoffweightisFieldLengthLimited.

2.3.4.2 Actual Weight Less Than Limit Weight

Returningtotheoperationaltakeoffcalculation,thesecondstepistothencomparetheactualairplane weight to the Field Length Limit

Weight.Thereareonlytwopossibleoutcomesofthischeck.

1)TheactualairplaneweightcouldequalorexceedtheFieldLengthLimitWeight,or

2)TheactualairplaneweightislessthantheFieldLengthLimitWeight.

The first case is relatively straightforward, theairplaneweightcannotbegreaterthanthelimitweightandmustbereduced.TheresultisatakeoffataFieldLengthLimitWeightaswehavejustdiscussed.Thesecondcase,whichistypicalofmostjettransportoperations,isworthyoffurtherconsideration.

Byfar,themostlikelytakeoffscenarioforthelinepilotisthecasewheretheactualairplaneweightislessthananylimitweight,especiallytheFieldLengthLimitWeight.Italsoispossiblythemosteasilymisunderstoodareaoftakeoffperformancesincethefactthattheairplaneisnot at a limit weight is about all the flight crew candeterminefromthedatausuallyavailableonthe flight deck. Currently, few operators provide anyinformationthatwillletthecrewdeterminehowmuchexcessrunwayisavailable;whatitmeansintermsoftheV1speedtheyareusing;orhowtobestmaximizethepotentialsafetymarginsrepresentedbytheexcessrunway.

2.3.5 Factors that Affect Takeoff and RTO Performance

Both the continued and the rejected takeoffperformancearedirectlyaffectedbyatmosphericconditions, airplane configuration, runway characteristics, engine thrust available, andbyhumanperformancefactors.Thefollowingsectionsreviewtheeffectsofthesevariablesonairplaneperformance.Thepurposeisnottomake thisacomplete treatiseonairplaneperformance.Rather, it is to emphasize thatchanges in these variables can have a significant impactonasuccessfulGo/NoGodecision.Inmany instances, the flight crew has a degree of directcontroloverthesechanges.

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2.3.5.1 Runway Surface Condition

Theconditionoftherunwaysurfacecanhavea significant effect on takeoff performance, since it can affect both the acceleration anddeceleration capability of the airplane. Theactualsurfaceconditioncanvaryfromperfectlydrytoadamp,wet,heavyrain,snow,orslushcoveredrunwayinaveryshorttime.Theentirelengthoftherunwaymaynothavethesamestoppingpotentialduetoavarietyoffactors.Obviously, a 10,000-ft runway with the first 7,000feetbareanddry,butthelast3,000feeta sheetof ice,doesnotpresent averygoodsituationforahighspeedRTO.Ontheotherhand, there are also specially constructedrunways with a grooved or Porous FrictionCoat(PFC)surfacewhichcanofferimprovedbrakingunderadverseconditions.Thecrewscannotcontrol theweather like theycan theairplane’s configuration or thrust. Therefore, to maximizeboththe“Go”and“Stop”margins,they must rely on judiciously applying theircompany’swetorcontaminatedrunwaypoliciesaswellastheirownunderstandingofhowtheperformanceoftheirairplanemaybeaffectedbyaparticularrunwaysurfacecondition.

The certification testing is performed on a smooth,ungrooved,dryrunway.Forairplanescertified under FAR Amendment 25-92, testing isalsoperformedonsmoothandgroovedwetrunways.Anycontaminationnotcoveredinthecertification data which reduces the available frictionbetweenthetireandtherunwaysurfacewillincreasetherequiredstoppingdistanceforanRTO.Runwaycontaminantssuchasslushorstandingwatercanalsoaffectthecontinuedtakeoff performance due to “displacementand impingement drag” associated with thespray from the tires striking the airplane.Somemanufacturersprovideadvisorydataforadjustmentoftakeoffweightand/orV1whenthe runway is wet or contaminated. Manyoperators use this data to provide flight crews withamethodofdeterminingthelimitweightsforslipperyrunways.

Factorsthatmakearunwayslipperyandhowtheyaffectthestoppingmaneuverarediscussedinthefollowingsections.

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2.3.5.1.1 Hydroplaning

Hydroplaning is an interesting subject sincemostpilotshaveeitherheardoforexperiencedinstancesofextremelypoorbrakingactiononwetrunwaysduringlanding.Thephenomenonishighlysensitivetospeedwhichmakesitanespecially important consideration for RTOsituations.

As a tire rolls on awet runway, its forwardmotiontendstodisplacewaterfromthetreadcontactarea.Whilethisisn’tanyproblematlowspeeds,athighspeedsthisdisplacementaction can generate water pressures sufficient toliftandseparatepartofthetirecontactareafromtherunwaysurface.Theresultingtire-to-groundfrictioncanbeverylowathighspeedsbutfortunatelyimprovesasspeeddecreases.

Dynamic hydroplaning is the term used todescribe the reduction of tire tread contactareadue to inducedwaterpressure.Athighspeeds on runways with significant water, theforwardmotionofthewheelgeneratesawedgeofhighpressurewaterat the leadingedgeofthecontactarea,asshowninFigure16A.Dependingonthespeed,depthofwater,andcertaintireparameters,theportionofthetire tread thatcanmaintaincontactwith therunway varies significantly. As the tread contact areaisreduced,theavailablebrakingfrictionisalsoreduced.Thisisthepredominantfactorleading to reduced friction on runways thathave either slush, standing water or significant

waterdepthduetoheavyrainactivity.Intheextremecase,totaldynamichydroplaningcanoccurwhere the tire to runwaycontact areavanishes,thetireliftsofftherunwayandridesonthewedgeofwaterlikeawaterski.Sincetheconditionsrequiredtoinitiateandsustaintotal dynamic hydroplaning are unusual, itis rarely encountered. When it does occur,suchasduringanextremelyheavyrainstorm,it virtually eliminates any tire braking orcorneringcapabilityathighspeeds.

Another form of hydroplaning can occurwhere there is some tread contact with therunwaysurfacebutthewheeliseitherlockedor rotating slowly (compared to the actualairplane speed). The friction produced bytheskiddingtirecausesthetreadmaterialtobecomeextremelyhot.AsindicatedinFigure16B,theresultingheatgeneratessteaminthecontactareawhichtendstoprovideadditionalupwardpressureonthetire.Thehotsteamalsostartsreversingthevulcanizingprocessusedin manufacturing the rubber tread material.The affected surface tread rubber becomesirregularinappearance,somewhatgummyinnature,andusuallyhasalightgraycolor.This“reverted”rubberhydroplaningresultsinverylowfrictionlevels,approximatelyequaltoicyrunwayfrictionwhenthetemperatureisnearthemeltingpoint.Anoccurrenceofrevertedrubberhydroplaningisrareandusuallyresultsfromsomekindofantiskid systemorbrakemalfunctionwhichpreventedthewheelfromrotatingattheproperspeed.

Figure 16ADynamic Hydroplaning

Figure 16BReverted Rubber Hydroplaning

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In the last several years, many runwaysthroughout the world have been grooved,thereby greatly improving the potential wetrunway friction capability. As a result, thenumberofhydroplaningincidentshasdecreasedconsiderably.Flighttestsofonemanufacturer’sairplane on a well maintained groovedrunway,whichwasthoroughlydrenchedwithwater, showed that the stopping forceswereapproximately90%oftheforcesthatcouldbedevelopedonadryrunway.Continuedeffortstogrooveadditionalrunwaysortheuseofotherequivalenttreatmentssuchasporousfrictionoverlays, will significantly enhance the overall safetyoftakeoffoperations.

The important thing to rememberaboutwetorcontaminatedrunwayconditionsisthatforsmoothrunwaysurfacesthereisapronouncedeffect of forward ground speed on frictioncapability,aggravatedbythedepthofwater.Forproperlymaintainedgroovedorspeciallytreated surfaces, the friction capability ismarkedlyimproved.

2.3.5.1.2 The Final Stop

Areviewofoverrunaccidentsindicatesthat,inmanycases,thestoppingcapabilityavailablewas not used to the maximum during theinitialandmidportionsofthestopmaneuver,becausethereappearedtobe“plentyofrunwayavailable”.Insomecases,lessthanfullreversethrustwasusedandthebrakeswerereleasedforaperiodoftime,lettingtheairplanerollontheportionoftherunwaythatwouldhaveproducedgoodbrakingaction.Whentheairplanemovedonto the final portion of the runway, the crew discoveredthatthepresenceofmoistureonthetopofrubberdepositsinthetouchdownandturnoff areas resulted in very poor brakingcapability,andtheairplanecouldnotbestoppedontherunway.WhenanRTOisinitiatedonwetorslipperyrunways,itisespeciallyimportanttousefullstoppingcapabilityuntiltheairplaneiscompletelystopped.

2.3.5.2 Atmospheric Conditions

Ingeneral,theliftthewingsgenerateandthrusttheenginesproducearedirectlyrelatedtotheairplane’sspeedthroughtheairandthedensityof that air. The flight crew should anticipate thattheairplane’stakeoffperformancewillbeaffectedbywindspeedanddirectionaswellastheatmosphericconditionswhichdetermineairdensity.ProperlyaccountingforlastminutechangesinthesefactorsiscrucialtoasuccessfulGo/NoGodecision.

Theeffectofthewindspeedanddirectionontakeoffdistanceisverystraightforward.Atanygivenairspeed,a10-knotheadwindcomponentlowers the ground speed by10knots. SinceV1, rotation, and liftoff speeds are at lowergroundspeeds,therequiredtakeoffdistanceis reduced. The opposite occurs if the windhasa10-knottailwindcomponent,producinga10-knotincreaseinthegroundspeed.Therequiredrunwaylengthisincreased,especiallythedistancerequiredtostoptheairplanefromV1. Typical takeoff data supplied to the flight crew by their operations department willeitherprovidetakeoffweightadjustmentstobeappliedtoazerowindlimitweightorseparatecolumns of limit weights for specific values of wind component. In either case, it is theresponsibility of the flight crew to verify that lastminutechangesinthetowerreportedwindsareincludedintheirtakeoffplanning.

Theeffectofairdensityontakeoffperformanceisalsostraightforwardinsofarasthecrewisnormallyprovidedthelatestmeteorologicalinformationpriortotakeoff.However,itistheresponsibilityofthecrewtoverifythecorrectpressurealtitudeandtemperaturevaluesusedin determining the final takeoff limit weight andthrustsetting.

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2.3.5.3 Airplane Configuration

The planned configuration of the airplane at the timeoftakeoffmustbetakenintoconsiderationby the flight crew during their takeoff planning. This should include the usual things like flap selection, and engine bleed configuration, as well as the unusual things like inoperativeequipmentcoveredbytheMinimumEquipmentList (MEL) or missing items as covered bythe Configuration Deviation List (CDL). This sectionwilldiscusstheeffectoftheairplane’sconfiguration on takeoff performance capability and/or the procedures the flight crew would use tocompleteorrejectthetakeoff.

2.3.5.3.1 Flaps

The airplane’s takeoff field length performance is affected by flap setting in a fairly obvious way. Foragivenrunwaylengthandairplaneweight,thetakeoffspeedsarereducedbyselectingagreater flap setting. This is because the lift required for flight is produced at a lower V2speed with the greater flap deflection. Since the airplanewillreachtheassociatedlowerV1speedearlierinthetakeoffroll,therewillbemorerunwayremainingforapossiblestopmaneuver.Onthe“Go”sideofthedecision,increasingthe takeoff flap deflection will increase the airplane drag and the resulting lower climbperformancemaylimittheallowabletakeoffweight.However,thetakeoffanalysisusedbythe flight crew will advise them if climb or obstacleclearanceisalimitingfactorwithagreater flap setting.

2.3.5.3.2 Engine Bleed Air

Wheneverbleedairisextractedfromanengine,andthevalueofthethrustsettingparameterisappropriatelyreduced,theamountofthrusttheenginegeneratesisreduced.Therefore,theuseof enginebleedair for air conditioning/pressurizationreducestheairplane’spotentialtakeoffperformanceforagivensetofrunwaylength,temperatureandaltitudeconditions.

When required, using engine and/or winganti-ice further decreases the performanceon someairplanemodels.This “lost” thrustmay be recoverable via increased takeoffEPRorN1limitsasindicatedintheairplaneoperatingmanual.Itdependsonenginetype,airplane model, and the specific atmospheric conditions.

2.3.5.3.3 Missing or Inoperative Equipment

Inoperative or missing equipment cansometimes affect the airplane’s accelerationor deceleration capability. Items whichare allowed to be missing per the certified Configuration Deviation List (CDL), such asaccesspanelsandaerodynamicseals,cancauseairplanedragtoincrease.Theresultingdecrements to the takeoff limit weights are,when appropriate, published in the CDL.Withthesedecrementsapplied,theairplane’stakeoffperformancewillbewithintherequireddistancesandclimbrates.

Inoperativeequipmentordeactivatedsystems,aspermittedundertheMinimumEquipmentList (MEL) can also affect the airplane’sdispatched “Go” or “Stop” performance.For instance, on some airplane models, aninoperative in-flight wheel braking system may require the landing gear to be left extendedduring a large portion of the climbout toallow the wheels to stop rotating. The ‘Go”performancecalculationsfordispatchmustbemade in accordance with certified “Landing GearDown”FlightManualdata.Theresulting

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new limit takeoff weight may be much lessthantheoriginallimitinordertomeetobstacleclearance requirements, and there would besomeexcess runwayavailable for a rejectedtakeoff.

AnMELitemthatwouldnotaffectthe“Go”performance margins but would definitely degradethe“Stop”marginsisaninoperativeanti-skidsystem.Inthisinstance,notonlyisthelimitweightreducedbytheamountdeterminedfrom the AFM data, but the flight crew may also berequiredtouseadifferentrejectedtakeoffprocedure in which throttles are retarded first, the speedbrakes deployed second, and thenthebrakesareappliedinajudiciousmannertoavoidlockingthewheelsandfailingthetires.3TheassociateddecrementintheFieldLengthLimitWeightisusuallysubstantial.

OtherMELitemssuchasadeactivatedbrakemay impact both the continued takeoff andRTOperformancethroughdegradedbrakingcapability and loss of in-flight braking of the spinningtire.

The flight crew should bear in mind that the performance of the airplane with thesetypesofCDLorMELitemsintheairplane’smaintenancelogatdispatchwillbewithinthecertified limits. However, it would be prudent for the flight crew to accept final responsibility toassurethat theitemsareaccountedfor inthedispatchprocess,andtoinsurethatthey,asacrew,arepreparedtoproperlyexecuteanyrevisedprocedures.

3UKCAAprocedureadds“...applymaximumreversethrust.”

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2.3.5.3.4 Wheels, Tires, and Brakes

The airplane’s wheels, tires, and brakes areanotherareathatshouldbeconsideredinlightof the significant part they play in determining theresultsofaGo/NoGodecision.

One design feature which involves all threecomponents is the wheel fuse plug. All jettransportwheelsusedforbrakingincorporatethermalfuseplugs.Thefunctionofthefuseplugistopreventtireorwheelburstsbymeltingiftheheattransferredtothewheelsfromthebrakesbecomes excessive. Melting temperatures offuseplugsareselectedsothatwithexcessivebrake heat, the inflation gas (usually nitrogen) is released before the structural integrity ofthetireorwheelisseriouslyimpaired.Bothcertification limitations and operationalrecommendationstoavoidmeltingfuseplugsareprovidedtooperatorsbythemanufacturer,asisdiscussedinSection2.3.5.3.6undertheheading,ResidualBrakeEnergy.

While fuse plugs provide protection fromexcessive brake heat, it is also important to

recognizethatfuseplugscannotprotectagainstall types of heat induced tire failures. Thelocationofthefusepluginthewheelisselectedtoensureproperresponsetobrakeheat.Thislocationincombinationwiththeinherentlowthermalconductivityoftirerubbermeansthatthefuseplugscannotpreventtirefailuresfromtherapidinternalheatbuildupassociatedwithtaxiing on an underinflated tire. This type of heat buildupcancauseabreakdownoftherubbercompound,plyseparation,and/orruptureoftheplies.Thisdamagemightnotcauseimmediatetirefailureandbecause it is internal, itmaynotbeobviousbyvisualinspection.However,theweakenedtireismorepronetofailureonasubsequent flight. Long taxi distances especially athighspeedsandheavytakeoffweightscanaggravatethisproblemandresultinablowntire. While underinflation is a maintenance issue, flight crews can at least minimize the possibilityoftirefailuresduetooverheatingbyusinglowtaxispeedsandminimizingtaxibrakingwheneverpossible.

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Correct tire inflation and fuse plug protection are significant, but will never prevent all tire failures. Foreign objects in parking areas,taxiwaysandrunwayscancauseseverecutsintires.Theabrasionassociatedwithsustainedlockedorskiddingwheels,whichcanbecausedbyvariousantiskidorbrakeproblems,cangrindthroughthetirecordsuntilthetireisseverelyweakenedorablowoutoccurs.Occasionally,wheel cracks develop which deflate a tire and generateanoverloadedconditionintheadjacenttireonthesameaxle.Someoftheseproblemsareinevitable.However,itcannotbeoverstressedthat proper maintenance and thorough walkaroundinspectionsarekeyfactorsinpreventingtirefailuresduringthetakeoffroll.

Tire failures may be difficult to identify from the flight deck and the related Go/No Go decision isthereforenotasimpletask.Atireburstmaybeloudenoughtobeconfusedwithanenginecompressorstall,mayjustbealoudnoise,ormaynotbeheard.A tire failuremaynotbefeltatall,maycausetheairplanetopulltooneside,orcancausetheentireairplanetoshakeandshuddertotheextentthatinstrumentsmaybecome difficult to read. Vibration arising out of failureofanosewheeltirepotentiallypresentsanothercomplication.Duringtakeoffrotation,vibrationmayactuallyincreaseatnosewheelliftoffduetothelossofthedampeningeffectofhavingthewheelincontactwiththerunway.Apilotmustbecautiousnottoinappropriatelyconclude, under such circumstances, thatanotherproblemexists.

Although continuing a takeoff with a failedtire will generally have no significant adverse results,theremaybeadditionalcomplicationsasaresultofatirefailure.Failedtiresdonotinthemselvesusuallycreatedirectionalcontrolproblems.Degradationofcontrolcanoccur,however, as a result of heavy pieces of tirematerialbeingthrownatveryhighvelocitiesandcausingdamagetotheexposedstructureof the airplane and/or the loss of hydraulicsystems. On airplanes with aft mountedengines,thepossibilityofpiecesofthefailed

tirebeingthrownintoanenginemustalsobeconsidered.

An airplane’s climb gradient and obstacleclearance performance with all enginesoperatingandthelandinggeardownexceedsthe minimum certified engine-out levels that areusedtodeterminethetakeoffperformancelimits.Therefore,leavingthegeardownafterasuspectedtirefailurewillnotjeopardizetheaircraftifallenginesareoperating.However,iftheperceivedtirefailureisaccompaniedbyanindicationofthrustloss,orifanengineproblemshoulddeveloplaterinthetakeoffsequence,theairplane’sclimbgradientand/orobstacleclearance capability may be significantlyreducedifthelandinggearisnotretracted.Thedecision toretract thegearwithasuspectedtireproblemshouldbeinaccordancewiththeairline’s/manufacturer’srecommendations.

Ifatirefailureissuspectedatfairlylowspeeds,it should be treated the same as any otherrejectable failure and the takeoff should berejectedpromptly.Whenrejectingthetakeoffwithablowntire,thecrewshouldanticipatethatadditionaltiresmayfailduringthestopattempt and that directional control may bedifficult. They should also be prepared for the possiblelossofhydraulicsystemswhichmaycausespeedbrakeorthrustreverserproblems.Sincethestoppingcapabilityoftheairplanemaybe significantly compromised, the crew should notrelaxfromamaximumeffortRTOuntiltheairplaneisstoppedonthepavement.

Rejecting a takeoff from high speeds witha failed tire is a much riskier proposition,especiallyiftheweightisneartheFieldLimitWeight.Thechancesofanoverrunareincreasedsimplyduetothelossofbrakingforcefromonewheel.Ifadditionaltiresshouldfailduringthestopattempt,theavailablebrakingforceisevenfurtherreduced.Inthiscase,itisgenerallybettertocontinuethetakeoff,ascanbeseeninFigure17.Thesubsequentlandingmaytakeadvantageofalowerweightandspeedifitispossibletodumpfuel.Also,thecrewwillbe

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betterprepared forpossiblevibrationand/orcontrolproblems.Mostimportant,however,isthefactthattheentirerunwaywillbeavailableforthestopmaneuverinsteadofperhaps,aslittleas40%ofit.

As can be seen from this discussion, it isnot a straightforward issue to define when a takeoffshouldbecontinuedorrejectedaftera suspected tire failure. It is fairly obvioushowever,thatanRTOinitiatedathighspeedwithasuspectedtirefailureisnotapreferredsituation. McDonnell Douglas Corporation,inanAllOperatorLetter4,hasaddressedthisdilemma by recommending a policy of notrejectingatakeoffforasuspectedtirefailureat speedsaboveV1−20 knots. The operators of other model aircraft should contact themanufacturer for specific recommendations regardingtirefailures.

2.3.5.3.5 Worn Brakes

TheinvestigationofonerecentRTOincident

whichwasinitiated“verynearV1”,revealedthattheoverrunwastheresultof8ofthe10wheel brakes failing during the RTO. Thefailed brakes were later identified to have been atadvancedstatesofwearwhich,whilewithinacceptedlimits,didnothavethecapacityforahighenergyRTO.

This was the first and only known accident in thehistoryofcommercialjettransportoperationthatcanbetracedtofailureofthebrakesduringanattemptedRTO.TheNationalTransportationSafetyBoard(NTSB)investigatedtheaccidentandmadeseveralrecommendationstotheFAA.The recommendations included the need torequireairplaneandbrakemanufacturers toverifyby testandanalysis that theirbrakes,whenworntotherecommendedlimits,meetthe certification requirements. Prior to 1991, maximumbrakeenergylimitshadbeenderivedfromtestsdonewithnewbrakesinstalled.

Virtually all brakes in use today have wearindicatorpinstoshowthedegreeofwearandwhen the brake must be removed from the

•

Figure 17 Margins associated with continuing or rejecting a takeoff with a tire failure

4McDonnellDouglasAllOperatorsLetterFO-AOL-8-003,-9-006,-10-004,-11-015,Reiteration of Procedures and Techniques Regarding Wheels, Tires, and Brakes,dated19AUG1991

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airplane.Inmostcases,asthebrakewears,thepinmovesclosertoareferencepoint,sothatwhen the end of the pin is flush with the reference (withfullpressureapplied),thebrakeis“wornout”.Asoflate1991,testshavebeencompletedwhichshowthatbrakesattheallowablewearlimitcanmeetAFMbrakeenergylevels.Asa result, “wear pin length” is not significant to the flight crew unless the pin indicates that thebrakeiswornoutandshouldberemovedfrom service. There are no changes to flight crewordispatchproceduresbasedonbrakewearpinlength.

2.3.5.3.6 Residual Brake Energy

Afterabrakeapplication,theenergywhichthebrakehasabsorbedisreleasedasheatanduntilthisheatisdissipated,theamountofadditionalenergy which the brake can absorb withoutfailureisreduced.Therefore,takeoffplanningmust consider the effects of residual brakeenergy(orbraketemperature)ifthepreviouslanding involved significant braking and/or the airplaneturnaroundisrelativelyshort.Thereare two primary sources of information onthissubject.Thebraketemperaturelimitationsand/orcoolingchartsintheairplaneoperatingmanualproviderecommendedinformationontemperaturelimitationsand/orcoolingtimesand the procedures necessary to dissipatevariousamountsofbrakeenergy.Inaddition,the Maximum Quick Turnaround Weight(MQTW) chart in the AFM is a regulatoryrequirementthatmustbefollowed.Thischartshowsthegrossweightatlandingwheretheenergy absorbed by the brakes during thelanding could be high enough to cause thewheel fuse plugs to melt and establishes aminimumwaiting/coolingtimeforthesecases.TheMQTWchartassumesthatthepreviouslandingwasconductedwithmaximumbrakingfortheentirestopanddidnotusereversethrust,soformanylandingswhereonlylightbrakingwasusedthereissubstantialconservatismbuiltintothewaitrequirement.

2.3.5.3.7 Speedbrake Effect on Wheel Braking

Whilejettransportpilotsgenerallyunderstandthe aerodynamic drag benefit of speedbrakes andthecapabilityofwheelbrakestostopanairplane, theeffectofspeedbrakesonwheelbrakeeffectivenessduringanRTOisnotalwaysappreciated. The reason speedbrakes are socriticalistheirpronouncedeffectonwinglift.Depending on flap setting, the net wing lift can be reduced, eliminated or reversed to adownloadbyraisingthespeedbrakes,therebyincreasing the vertical load on the wheelswhich in turn can greatly increase brakingcapability.

Speedbrakes are important since for mostbraking situations, especially any operationonslipperyrunways,thetorqueoutputofthebrake,andthereforetheamountofwheelbrakeretardingforcethatcanbedevelopedishighlydependent on the vertical wheel load. As aresult,speedbrakesmustbedeployedearlyinthestoptomaximizethebrakingcapability.During RTO certification flight tests, the stoppingperformanceisobtainedwithpromptdeploymentofthespeedbrakes.Failure to raise the speedbrakes during an RTO or raising them late will significantly increase the stopping distance beyond the value shown in the AFM.

Figures 18 and 19 summarize the effect ofspeedbrakes during an RTO. For a typicalmid-sized two-engine transport,ata takeoffweightof225,000lb,thetotalloadonthemainwheelsatbrakereleasewouldbeapproximately193,000lb.Astheairplaneacceleratesalongtherunway,wingliftwilldecreasetheloadonthegear,andbythetimetheairplaneapproachesV1speed,(137knotsforthisexample),themaingearloadwillhavedecreasedbynearly63,000lb.ThedatainFigure19graphicallydepictshowtheforcesactingontheairplanevarywithairspeedfromafewknotsbeforetheRTOisinitiateduntiltheairplaneisstopped.WhenthepilotbeginstheRTObyapplyingthebrakesand

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Figure 18 Effect of speedbrakes on the stopping capability of a typical mid-size two-engine transport

Figure 19 Summary of forces during a typical mid-size two-engine airplane RTO

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closingthethrustlevers,thebrakingforcerisesquicklytoavalueinexcessof70,000lb.ThenearlyverticallinemadebythebrakingforcecurveinFigure19alsoshowsthattheairplanebegantodeceleratealmostimmediately,withvirtuallynofurtherincreaseinspeed.

Thenextaction ina typicalRTOprocedureistodeploythespeedbrakes.Bythetimethisaction is completed, and the wheel brakeshavebecomefullyeffective,theairplanewillhaveslowedseveralknots.Inthisexampleofan RTO initiated at 137 knots, the airspeedwouldbeabout124knotsat thispoint.Theweightonthemaingearat124knotswouldbeapproximately141,600lbwiththespeedbrakesdown,andwouldincreaseby53,200lbwhenthe speedbrakes are raised. The high speedbrakingcapabilityissubstantiallyimprovedbythis38%increaseinwheelloadfrom141,600to194,800pounds,whichcanbeseenbynotingtheincreaseinbrakingforceto98,000pounds.In addition, the speedbrakes have an effecton aerodynamicdrag, increasing it by73%,from8,500to14,700pounds.Thecombinedresult,asindicatedbythetableinFigure18,isthatduringthecritical,highspeedportionoftheRTO,thetotalstoppingforceactingonthe airplane is increased by 34% when thespeedbrakesaredeployed.

Sinceboth the force thebrakescanproduceandtheaerodynamiceffectofthespeedbrakesvarywithspeed,thetotaleffectfortheRTOstopismoreproperlyindicatedbyaveragingtheeffectof thespeedbrakesover theentirestoppingdistance.Forthisexample,theoveralleffectofraisingthespeedbrakesisanincreaseof14%intheaveragetotalstoppingforceactingthroughouttheRTO.

One common misconception among pilotsis that thequickuseof thrust reverserswilloffsetanydelayoreventhecompletelackofspeedbrakedeploymentduringanRTO.Thisissimplynottrue.Onadryrunway,delayingthe deployment of the speedbrakes by only5secondsduringtheRTOwilladdover300

ft.tothestopdistanceofatypicalmid-sizedtwo-enginejettransport,includingtheeffectsofengine-outreversethrust.Asaworstcaseillustration, if reverse thrust was not usedandthespeedbrakeswerenotdeployedatall,stoppingdistancewouldbeincreasedbymorethan 700 ft. Although the exact figures of this example will vary with different flap settings andfromoneairplanemodel toanother, thegeneraleffectwillbe thesame,namely thatspeedbrakeshaveaverypronouncedeffectonstoppingperformance.

2.3.5.3.8 Carbon and Steel Brake Differences

Recentemphasisontheapparenttendencyforcarbonbrakestowearoutinproportiontothetotalnumberofbrakeapplications,asopposedtosteelbrakeswhichwearoutinproportiontoenergyabsorbedbythebrakes,hasgeneratedinterest in other operational differencesbetween the two typesofbrakes.While theemphasis on wear difference is necessary,sincetheeconomicsofbrakemaintenanceissosignificant, for most other operational aspects thetwobrakescanbeconsideredequivalent.

AsfarasRTOcapabilityisconcerned,thetypeofbrakeinvolveddoesnotmattersinceeachbrake installation is certified to its particular takeoff energy capability. This means thateithercarbonorsteelbrakes,evenfullyworn,will be able to perform the maximum certified RTOconditionapplicabletothatinstallationinasatisfactorymanner.

Onedifferencebetweensteelandcarbonbrakesthatisoftenclaimedisanincreasedtoleranceto thermal overload. To understand this inproperperspective,recognizethatalthoughthefrictionelements inacarbonbrake(rotatingand stationary disks) are made of carbonmaterial,whichhasgoodstrengthandfrictioncharacteristicsathightemperatures,thebrakestructure, brake hydraulics, the wheel, andthetireareessentiallythesameasusedforanequivalentsteelbrake.Withinthelimitations

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representedbythisnon-carbonequipmentthen,anoverheatedcarbonbrakewillcontinue tofunctionreasonablywell insituationswherean equivalent steel brake with its metallicdisksmightnot.Anoverloadconditioncouldbecausedbyexcessivetaxibraking,ridingthebrakes,orinappropriateturnaroundproceduresafterlanding.Inthistypeofsituation,carbonbrakeswillgenerallydemonstratebetterfrictioncharacteristics and therefore develop moretorqueandstoppingforcethanequivalentsteelbrakes.

The difficulty with this carbon brake thermal advantageisthatitisnearlyimpossibletojudgetheextraamountofbrakingthatcouldbedonebeforeaffectingtheabilityofthenon-carboncomponentstoperforminanRTOsituation.Thisisbecausethethermaleffectsonthelimitinghardware are so highly time and ambientconditiondependent.Forinstance,whetheranairplanehascarbonbrakesorsteelbrakeswillnotmatterifenoughtimehaselapsedafteraheavybrakeapplicationsuchthatthewheelfuseplugsreleasebeforetheairplanecancompletethenexttakeofforasubsequentRTOattempt.Pilots should concentrate on proper brakingproceduresratherthanattempttocapitalizeonanyextracarbonbrakeadvantage.Attentionto thebrakecoolingchart recommendationswillavoidthesethermalproblemsandensurethattheairplanestoppingperformancecanbeachievedregardlessofwhethersteelorcarbonbrakesareinstalled.

Theincreasedthermaloverloadcapabilityofcarbonbrakesiscloselyrelatedtotheideathatcarbonbrakesdonot“fade”.Inotherwords,theyalwaysproducethesametorquethroughoutthestopevenasthebraketemperatureincreases.Although many carbon brakes do developnearlyconstanttorque,somefadeconsiderablyincertainconditions.Ontheotherhand,somesteel brakes do not fade very much at all,dependingtoalargeextentonthedegreeofconservatismbuiltintothebrake.Ineithercase,brakefadeistakenintoaccountintheAFMperformance, for the specific brake installed on

eachparticularairplane.Therefore,brakefadedoesnotneedtobeanoperationalconcerntothe flight crew.

Asecondfactorwithsteelbrakesisthepotentialloss of structural strength of the rotors andstatorsattheextremeoperatingtemperaturesassociatedwith limitingenergyvalues.Thiscouldcauseastructuralfailureofoneormorebrakestatorsneartheendofthestop.Inthiscase thebrakewill continue to functionbutwithreducedtorquecapability.Theremainingcomponents,whicharecommontocarbonandsteelbrakes,arelesslikelytobeaffected.

An RTO from at or near the brake energylimits can also mean that after stopping ontherunway,thebrakesmaynotbecapableofstoppingtheairplaneagain,evenfromlowtaxispeeds.Thisisespeciallytrueforsteelbrakesduetotheincreasedchanceofstructuralfailure.Therefore,itisimportantthatthecrewconsidertheprobableconditionoftheairplanewheels,brakes,andtiresaftercompletingahighspeedRTObeforeattemptingtomovetheairplanefromtherunway.

OneotherdifferencebetweencarbonandsteelbrakesthatmightbeevidentincertainRTOsisbrakewelding.Steelbrakes,whichusuallyhaverotorsofsteelandstatorsofacopper-ironmix(withanumberofspecialingredients)canweldtogether,preventingfurtherwheelrotation.Thiscanevenhappenbeforetheairplanecomestoafullstop,particularlyinthelastseveralknotswheretheantiskidsystemisnoteffective.

2.3.5.3.9 High Brake Energy RTOs

Brakerotorandstatortemperaturesassociatedwith RTOs which involve brake energiesat or near certified maximum values, reach approximately2000 °F for steelbrakes, and2500°Fformostcarbonbrakes.Thesehightemperaturesmay, insomesituations, ignitecertain items in the wheel, tire, and brakeassembly.Whileconsiderabledesigneffortis

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made to preclude fires whenever possible, the regulationsrecognizetherarityofsuchhighenergy situations and allow brake fires after a maximumenergycondition,providedthatanyfires that may occur are confined to the wheels, tiresandbrakes,anddonotresultinprogressiveengulfmentoftheremainingairplaneduringthetimeofpassengerandcrewevacuation.Itisimportant then, for flight crews to understand the nature of possible fires and the airplane takeoff parameters that could involve theseveryhighbrakeenergies.

There are two primary combustibles in theassembly,namelythetire,andbrakegrease.Brake hydraulic fluid will also burn if there is a hydraulic leak directed at a very hotbrake disk. Tire fires can occur if the rubber compoundtemperatureexceedsapproximately650 °F. Tire fires usually burn fairly slowly for the first several minutes when started by brake heat. Grease fires are even less active, typically involving a small, unsteady, flickering flame, sometimes with considerable smoke. Theprobabilityofacrewexperiencingabrakefire at the conclusion of an RTO is very low, consideringbrakedesignfactors,thedispatchparameters,andservicehistory.

In terms of practical guidelines for flight crews,takeoffsatornearVMBEarenormallyencountered at high altitude airports or atveryhottemperatures.AnRTOfromclosetoV1speedundertheseconditionswillrequirethe brakes to absorb a significant amount of

energyduringthestop.FlightcrewscanusetheBrakeCoolingChartoftheairplaneoperatingmanual to determine brake energyvalues ifthesituationwarrantssuchareview.Incaseswhereanextremelyhighbrakeenergymightbe encountered, the possibility of a brake fire should therefore be considered by the flight crew during the pre-takeoff briefing. If a high speed RTO is subsequently performed, thetowershouldimmediatelybeadvisedthattheairplaneisstillontherunway,thatahighbrakeenergy stop was made, and that emergencyequipmentisrequestedtoobservethetiresandbrakes for possible fires.

2.3.5.4 Reverse Thrust Effects

Mostofthetakeoffsplannedintheworlddonotincludereversethrustcredit.Thisisbecausethe rejected takeoff certification testing under FAArulesdoesnotincludetheuseofreversethrust, except for the wet runway case forairplanes certified under FAR Amendment 25-92.Anadditionalstoppingmarginisproducedbyusingmaximumreversethrust.Westresstheword“maximum”inrelationtotheuseofreversethrustbecauseofanothercommonlyheld misconception. Some pilots are of theopinion that idle reverse is “equallyor evenmore”effectivethanfullormaximumreversethrust for today’shighbypass ratioengines.Thisissimplynottrue.ThemoreEPRorN1that isapplied in reverse, themorestoppingforce the reverse thrust generates. The data

Figure 20Effect of engine

RPM and airspeed on reverse thrust of a typical high

bypass engine

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showninFigure20istypicalforallhighbypassengines.

Onwetorslipperyrunways,thewheelbrakesarenotcapableofgeneratingashigharetardingforceastheyareonadrysurface.Therefore,theretardingforceofthereversersgeneratesalargerpercentageofthetotalairplanedeceleration.

2.3.5.5 Runway Parameters

Runway characteristics which affect takeoffperformance include length, slope, clearwayand/orstopway.Theeffectofrunwaylengthisstraightforward,however,slope,clearway,andstopwaydeservesomediscussion.

A single value of runway slope is typicallychosen by the operator to perform takeoffanalysis calculations. This single value isusuallytakenfrominformationpublishedbythe navigation chart services or the airportauthorities.Oncloserinspectionhowever,manyrunwaysareseentohavedistinctdifferencesin slope along the length of the runway.The single published value may have beendeterminedbyavarietyofmethods,rangingfrom a simple mathematical average of thethresholdelevations,tosomeweightedaveragemethods proposed by ICA0 in an advisorypublication5.

As a simple example, consider a runwaywhichhasonlyoneslopediscontinuity.Thefirst two thirds of the runway has an uphill slopeof+2%andthelastthirdhasadownhillslope of −2%. The equivalent single slope for this runway, as determined from the ICAOCircularmethods,couldvaryfrom+1.3%to−0.3%. When the takeoff analysis is made forthisrunway,thelimitweightswillbethesame as would be determined for an actualsinglesloperunway.However,astheairplanecommencesatakeoffonthe2%upsloperunway,itwillacceleratemoreslowlythanitwouldonany of the equivalent single slope runways,which will result in its achieving V1 speed

further along the runway thanwasplanned.IfnoeventoccurswhichwouldprecipitateanRTO, the final acceleration to VRandliftoffwill be higher than planned and the overallperformancewillprobablycomeoutclosetowhatwasscheduled.

Ontheotherhand,ifaneventworthyofanRTOshouldoccurjustpriortotheairplanereachingV1,most,ifnotallofthestopmaneuverwillhavetobecarriedoutona2%downhillslopesurfaceinsteadoftheequivalentsingleslopevalue, and theRTOwillhavebeen initiatedwithlessrunwayremainingthanwasassumedindeterminingthelimitweightforthattakeoff.Thereislittlethecrewcandointhistypeofsituation,otherthanintheveinofsituationalawareness, emphasize in their briefing that an RTO near V1 for anything other than acatastrophiceventisnotadvisable.

A clearway is an area at least 500 ft widecentered about the extended centerline oftherunwaywithaslopeequaltoorlessthan1.25%.Thisareaiscalledtheclearwayplane.No obstructions, except threshold lights,canprotrudeabovethisclearwayplane.TheaccelerationtoV2and35feetiscompletedovertheclearway.Theuseofclearwaytoincreasetakeoffweight“unbalancestherunway”andresults in a lower V1 speed. The maximumclearwayusedtocalculatetakeoffperformanceisrestrictedbytheregulationstoonehalfthedemonstrateddistancefromliftoffto35ft.

Astopway isanareaat leastaswideas therunway and centered about the extendedcenterline. It must be capable of supportingthe weight of the airplane without causingdamage.Useofstopwayalso“unbalancestherunway”resultinginahighertakeoffweightandincreasedV1speed.AnRTOinitiatedatthisV1willcometoastoponthestopway.Forthesakeofcompleteness,itshouldbepointedoutthatnotallstopwayswillqualifyasclearways,norwill a clearwaynecessarilyqualify as astopway. The specified criteria for each must bemetindependentlybeforeitcanbeusedfor

5ICAOCircular91-AN/75,The Effect of Variable Runway Slopes on Take-Off Runway Lengths for Transport Aeroplanes,dated1968.

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takeoffperformancecalculations.

Theuseofclearwayand/orstopwaydoesnotnecessarilyofferanyadditionalmarginforRTOstopping.Inbothcases,thetakeoffperformanceis“unbalanced”byadjustingV1speedtoplanthatthestopwillbecompletedbytheendofthepavedsurface.

2.3.5.6 (Not Used)

2.3.5.7 Takeoffs Using Reduced Thrust

Therearetwomethodsofperformingareducedthrust takeoff. The first is to use a fixed derate of theenginetoalowerthrustrating.Forexample,aJT9D-7FengineoperatedataJT9D-7rating,oraCFM56-3C-1engineoperatedat20,000lbofthrust(-B1rating)insteadofthefull23,500lb rating. When a fixed derate is used, the engine EGTandRPMlimitsarereducedandthecrewarenottoexceedthereducedlimitsinnormaloperation.Asaresultofthelowerlimitthrustwith a fixed derate, the minimum control speeds VmcgandVmcaarealsoreduced.Sincethechoiceofderatethrustlevelsisusuallyrestrictedtooneortwopreselectedvalues,itisrarethatthetakeoffperformanceatthederatedthrustwould be reduced to field length limit levels.

ThesecondwayofreducingtakeoffthrustistousetheAssumedTemperatureMethod.Thefundamental difference between fixed derates andtheAssumedTemperatureMethodisthattheoperatinglimitsoftheenginearenotreducedwhen using Assumed Temperature Methodreduced thrust. The flight crew may increase thethrusttothefullengineratingatanytimeduringthetakeoffifitisdeemedappropriate.For instance, British CAA Flight Manualsincludearecommendationtoincreasethrustontheoperatingenginestothefullratingintheeventthatanenginefailsduringthetakeoff.Asaresult,theVmcgandVmcaspeedsarenotreducedbelowthefullratingvalueswhenusingtheAssumedTemperatureMethod.

FixedderatesandtheAssumedTemperatureMethodalsodifferintermsoftheperformancemarginsthatareinherenttotheiruse.Aswaspreviouslymentioned,atlimitweights,atakeoffperformed using a fixed derate takeoff thrust will conform to the minimum performancelevelsoftheregulations,justasalimitweighttakeoff would when using full rated takeoffthrust.TheassociatedV1speedprovidesthestandard certification “margins” of a 35 foot screenheightorastopattheendoftherunwayintheeventofanenginefailure.

WhenusingtheAssumedTemperatureMethod,additional“margins”arecreated inboth the“Go”and“Stop”cases.Asthenameimplies,thetechniqueusedtocalculatetheperformancewiththeAssumedTemperatureMethodistoassumethatthetemperatureishigherthanitactuallyis,andtocalculatetakeoffthrustandspeedsatthehighertemperature.

TheprimaryreasonthattheuseoftheAssumedTemperatureMethod results in performancemargins is that the true airspeed of theairplaneislowerthanwouldbethecaseiftheactualtemperaturewereequaltotheassumedtemperature.

2.3.5.8 The Takeoff Data the Pilot Sees

The typical takeoff data table (sometimesreferredtoasrunwayanalysisorgrossweighttables) shows the limit takeoff weight fora specific runway over a range of ambient temperatures.Theremayalsobecorrectionsforwind, pressure altitude, bleed configurations, and runway surface conditions. Each tableusuallyshowsthelimitweightsforonlyoneflap setting. Some airlines show the takeoff speedsandthetakeoffthrustEPRorN1settingalongwiththelimitweights.ThetablescandisplaylimitweightsforFieldLength,Climb,Obstacle Clearance, Tire Speed and BrakeEnergy,andtellwhichfactorislimitingforeachwindandtemperature.Thistabulardisplayofthetakeoffdatahasbecomethestandardtool

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forusingtheassumedtemperaturemethodtoreducethetakeoffpowersettingandtherebyimproveenginelife.

Thistakeoffdataissomeofthemostimportantdata used on any flight. It is essential that flight crews know their actual takeoff weight and that theyuse theproper takeoff speeds.It is equally important that the flight crew be awareoftheirproximitytothelimitweightsfor that takeoff’s ambient conditions. Theselimitweights and speeds aremore than justnumbers. They represent the maximum certified takeoffperformanceoftheairplane.Iftheactualtakeoffweightisequaltoorneartherunwaylimit weight, the crew should note that factandbeextraalertthatarejectfromnearoratV1willrequirepromptapplicationofthefullstoppingcapabilityof theairplane to assurestoppingontherunway.

If theactualairplaneweight is less than thelimitweight,thecrewshouldtreatthenormallyobtainedV1 speedasa“limit speed”unlesstheiroperationsdepartmenthasprovidedthemwith a specific method of unbalancing the V1speedtoutilizetheexcessrunwayavailable.The operator should assure that a suitable,non-ambiguousmethodofpresenting theV1speed is chosen,whether it is a balancedorunbalancedspeed.

2.3.6 Increasing the RTO Safety Margins

Thereareanumberofchoicesandtechniquesthecrewcanmakeandpracticethatwillincreasethe RTO margins for takeoff. Some involveairline policy and require the publication ofadditional data (such as multiple flap setting takeoffweightandspeeddata)andsomearejustgoodpersonaltechnique.

2.3.6.1 Runway Surface Condition

The crew cannot control the weather likethey can the airplane’s configuration orthrust. Therefore, to maximize both the“Go”and“Stop”margins,theymustrelyonjudiciously applying their company’s wet orcontaminatedrunwaypoliciesaswellastheirownunderstandingofhowtheperformanceoftheirairplanemaybeaffectedbyaparticularrunwaysurfacecondition.

2.3.6.2 Flap Selection

OftentheRTOsafetymargincanbeincreasedby selection of an alternative takeoff flap setting. Consider for example, the effect of takeoff flap selectionontheperformancelimitweightsofatypicallargetwoengineairplane,asshowninFigure21.

8,700 ft runway Sea Level 37° C

Flap setting

1 5 15 20

Runway limit weight, lb (kg)

358,300 (162,494)

374,200 (169,705)

389,000 (176,417)

393,600 (178,503)

Climb/Obstacle limit weight, lb (kg)

414,100 (187,800)

407,300 (184,717)

393,600 (178,503)

383,000 (173,696)

Figure 21 Typical large two-engine jet transport takeoff performance

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If a flight requires the absolute maximum takeoffweight,theaboveweightlimitswoulddictatechoosingFlaps15since389,000lbisthehighestweightallowed.Flaps20isClimb/ObstaclelimitedtoalowerweightandFlaps1and5areRunwaylimitedtolowerweights.If the actual takeoffweightdesired is equalto the maximum limit weight, there is no flap selectionoption.ThetakeoffwillneedtouseFlaps15.

Moretypically,however,theairplane’sactualtakeoff weight is well below the maximum.There are then two viable ways to improveRTO stopping distance margin: either by flap selectionorbyreducedV1techniques.

If the flight’s actual takeoff weight was 374,200 pounds,investigatingtheabovetableindicatesFlaps5,Flaps15,orFlaps20areallacceptable.Flaps 5 is runway limited so it offers noadditionalRTOmargin.However,Flaps15andFlaps20bothofferanopportunityforadditionalstopping distance margin. These additionalstoppingmarginshavebeencalculatedforthisexampleandareshowninFigure22.

Thus,iftherearenootherconstraintssuchasobstaclesorcriticalnoiseabatementproceduresthat would prevent the selection of a greater flap setting,thecrewcouldgivethemselves1000feetofextrastoppingdistanceincaseanRTOwasrequiredonthistakeoff.

Rememberthattherearesomedisadvantagesto selecting a higher f lap setting. Thesedisadvantages include diminished climbperformanceandslightlymorefuelconsumeddue to the higher drag configuration and the additional flap retraction cleanup time that will berequired.

2.3.6.3 Runway Lineup

Positioning the aircraft on the runway inpreparationfortakeoffisanimportantelementinmaximizingtheamountofpavementavailableforapossibleRTOmaneuver.Correctiontotheavailable runway length canbemade to thetakeoff analysis on those runways where itisnotpossibletopositiontheairplaneatthebeginningofthepublisheddistance.

Correctrunwaylineuptechniqueshouldalwaysbepracticedregardlessofwhetherornotthereisexcessrunwayavailable.Evenifanallowancehasbeenmade,itisuptothecrewoperatingthe flight to align the airplane on the runway using the shortest possible distance. If theycandoitinashorterdistancethantakenintoaccountby theircompany, then there is thatmuchextramarginforthetakeoff.

2.3.6.4 Setting Takeoff Thrust

At takeoff thrust settings, gas turbine (jet)enginesoperateatveryhighRPM.Ittypicallytakesseveralsecondsfortheenginestospoolupfromalowidleortaxithrusttotakeoffpowerafter the thrust levers are advanced.Duringthis time, the aircraft is not accelerating atfullpotentialbecausetheenginesarenotyetdevelopingfullpower.

Thedemonstratedtakeoffdistanceisachievedwhenthetakeoffthrustissetpriortoreleasingthe brakes, but this technique is often notpractical in lineoperationsdue toexpedited

Flap setting 5 15 20

Stopping margin Zero 850 ft 1,000 ft

Figure 22Effect of flap

selection on RTO stopping margins

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takeoffclearances,engineFODhazards,andpassengercomfort.Asaresult,mosttakeoffsareperformedas“rollingtakeoffs”,withthethrustbeingsetastheairplanebeginsthetakeoffroll.However,thistechniquemustbeaccomplishedpromptly toavoidcompromising the takeoffperformance.Adelayedapplicationoftakeoffthrustwill increasethetimeanddistancetoreachV1speed.Consequently,lessrunwaywillbelefttostoptheairplaneshouldanRTObenecessary.Thethrustshouldbesetpromptly,according to the airframe manufacturer’srecommendations. The non-flying pilot or flight engineer then typically makes any final adjustmentsandmonitorstheenginesforanyabnormalities.

Onairplanesequippedwithautothrottles,anadditional item to be aware of is that someautothrottle systems incorporate “ThrustHold” features which will stop advancingthe thrust leversafter theairplanereachesapredetermined threshold airspeed value. Adelayinengagingtheautothrottlecanresultinthethruststabilizingbelowthetakeofftargetsettingandtheinitialaccelerationbeinglessthanrequired.

Theengineinstrumentsshouldbemonitoredclosely for any abnormal indications. PastRTOaccidentshaveoccurredafteranengineproblem was identified early in the takeoff roll, butnoactionwasinitiateduntiltheairplanehadreachedorexceededV1.

Company operations manuals or trainingmanualscontaincorrectproceduresforsettingtakeoff thrust. Observing these proceduresassures efficient engine acceleration and, as a consequence, proper aircraft accelerationthroughouttheentiretakeoffroll.

2.3.6.5 Manual Braking Techniques

Modulationofbrakepressureor“pumpingthebrakes”wasthewaymostpeopleweretaughtto apply automobile brakes when braking

conditions were less than favorable. Thispreventedsustainedskidsandthereforeaffordedboth better braking and directional control.Both benefits occur because a skidding tire produceslessfrictionalforcethanatirewhichcontinuestorotate.Flightdeckobservationandsimulatortesting,however,bothindicatethatthistechniquehasattimesbeencarriedoverintothecockpitofjettransports.Withtheantiskidcontrolsystemsinjettransportairplanesthistechnique is not onlyunnecessary, it resultsindegradedstoppingcapabilityandthereforeexcessive stopping distance especially foradverserunwayconditions.Proper braking technique in an RTO is to apply full brake pedal force (“stand on it”) and maintain full brake pedal force until the airplane comes to a complete stop.

Thepilot’sfootpositionrelativetotherudderpedalcanalsohaveaneffectontheachievementoffullbrakepressure.ItwasnotedduringastudyconductedbytheTrainingAidWorkingGroup6thatfootpositionduringthetakeoffrolltendstobeanindividualpreference.Somepilotsprefertohavetheirfeet“uponthepedals”tobereadytoapplyfullbrakesifrequired.Pilotswhopreferthistechniquealsonotedthattheirtoesare“curledback”toavoidunwantedbrakeapplicationswhenapplyingrudder.Theothertechnique is to rest the heels on the floor during thetakeoffroll,andthenraisethemtobeonthepedaltoapplyfullbraking.Noproblemswerenotedwitheithertechnique.

Onetechniquewhichdidnotworkwellwasalsonoted.Itisnotpossibletoapplymaximumbrake pedal deflection, and hence full brake pressure,iftheheelofthefootisleftonthefloor, unless the pilot has very big feet. In an RTOstopmaneuver,thefeetshouldbeupontherudderpedalsandsteady,heavypressureapplieduntiltheairplaneiscompletelystopped.Pilotsshoulddevelopahabitofadjustingtheirseatandtherudderpedalspriortoleavingthegate.Theabilitytoapplymaximumbrakepedalforceaswellasfullruddershouldbecheckedbybothpilots.

6TheTrainingAidWorkingGroupistheindustryandregulatoryteamthatdevelopedtheTakeoff Safety Training Aid.

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The importance of maintaining maximumbrakingandfullreversethrustduringanRTOuntiltheairplane“rockstoastop”cannotbeover-stressed. During a reject from V1, thegoal is safety, not passenger comfort. Theamountofdistancerequiredtodeceleratefromagivenspeedatthehighweightsassociatedwith takeoff is significantly greater than from thesamespeedatatypicallandingweight.Ifthepilottriestojudgetheamountofrunwayremaining against the current speed of theairplane,thevisualperceptionthattheairplanewillstopontherunway(“we’vegotitmade”),willpromptadecreaseinthestoppingeffort.ItispreciselyatthispointintheRTOthatthedifference between a successful Go/No Godecisionandanaccidentcanoccur.Thebrakesmaybenearingtheirenergyabsorptionlimitsandtheairplanemaybeenteringaportionoftherunwaycontaminatedwithrubberdeposits,whichcanbeveryslickifwet.InseveraloftheRTOaccidentsandincidentsofthepast,therewasexcessrunwayavailabletocompletethestop,but thepremature relaxationof thestoppingeffortcontributedtoanoverrun.

Anadditional consideration in completing asuccessfulRTOisthatthecrewshouldassesstheconditionoftheairplaneafteritcomestoastop.If there is evidence of a fire or other significant hazardtothepassengers,anevacuationontherunway is definitely preferable to “clearing theactive.”Everysecondcountsinanactualemergency evacuation. In at least one RTOaccident,manyofthefatalitieswerecausedbydelayingtheevacuationuntiltheaircraftwasclearoftherunway.

2.3.6.6 Antiskid Inoperative Braking Techniques

Antiskid inoperative dispatches represent aspecialcaseforbrakeapplicationtechniques.InthissituationthepilotexecutingtheRTOshouldapplysteadymoderatepedalpressureconsistent, in his judgement, with runwayconditions, airplanedispatchweight and the

availablerunwaylength.Fullbrakepressureshouldnotbeappliedwiththeantiskidsysteminoperativeduetotheriskoftirefailure.Tominimize the possibility of skidding a tire,whichcanleadtoablowout,thespeedbrakesshouldbedeployedbeforebrakesareapplied.Thisprovidesthehighestpossiblewheelloadstokeepthewheelsrotatingwiththeforwardmotionoftheairplane.

2.3.6.7 RTO Autobrakes

Autobrakesystemfunctionsandcrewactionstoinitiatethesefunctionsvaryfromoneairplanemodeltoanother.Forexample,somesystemsincludeautomaticspoilerextension,othersdonot.Therefore,traininginuseofthesystemmustbetailoredtotheparticularsysteminstalled.Thefollowingdiscussionillustratesthegeneralintentofautobrakesystems.

BrakeapplicationisanimmediatepilotactionwheninitiatinganRTO,andthisapplicationshouldbeofmaximumeffort.Anautomaticbrake application system called “RTOAUTOBRAKES”isbeinginstalledonmoreandmoreairplanestodaytoinsurethatthiscriticalstepisperformedasrapidlyaspossiblewhenanRTOisinitiated.Thissystemisdesignedtoautomaticallyapplymaximumbrakepressureifduringthetakeoffroll,allthethrustleversareretardedtoidle,andtheaircraftspeedisabove a specified value (usually 85-90 knots). RTOAutobrakestherefore,achievethesameairplane stopping performance as a proper,manualapplicationoffullfootpedalbraking.NotimedelaysarebuiltintotheRTOautobrakessuch as areused in some landing autobrakesettings.

Theuseof“RTOAUTOBRAKES”eliminatesany delay in brake application and assuresthat maximum effort braking is appliedpromptly.Possibleapplicationdelaysarisingfrom distractions due to directional controlrequirementsincrosswinds,orapplicationoflessthanmaximumbrakeforce,arecompletely

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eliminated. The results of a simulator studyconducted by the Training Aid WorkingGroup also suggest that, on the average,thoseRTOsperformedwithRTOautobrakesARMED resulted in more runway distanceremaining after the stop than did the RTOsperformed using manual braking only. Thisresult is more significant because few pilots left the autobrakes engaged for more thana few seconds before overriding them andapplyingfullmanualbraking.Thedifferencein stopping performance is attributed to thefirst few seconds of high deceleration with the autobrakesatfullpressure.

When theRTOautobrakes areARMED fortakeoff, the pilot not flying must monitor the system and advise the pilot flying if a DISARM condition occurs. The pilot flying should also monitor the deceleration of the airplane foracceptabilityandbepreparedtoapplymanualbraking if required or, the pilot performingthe rejectprocedure shouldapplymaximummanualbrakingduringtheRTO.InthislattercasearmingtheRTOautobrakefunctiononlyservesasabackupifforsomereasonmanualbrakingisnotapplied.

Thebrakepedalforcesrequiredtodisarmtheautobrakes may vary significantly between the landing autobrake settings and the RTOautobrakesettingofanygivenairplane,betweenoneairplanemodelandanotherof thesamemanufacturer,aswellasbetweenthevariousmanufacturers’airplanes.Itisnotsurprisingthat thispoint isnot fullyunderstood in thepilotcommunity.Itisimportantthatpilotsbemadeawareofhowthedetailsofanyparticularairplane’sautobrakesystemmightaffectRTOperformanceandthattheyobtainthenecessaryinformationfromtheirtrainingdepartment.

2.3.6.8 (Not Used)

2.3.6.9 The V1 Call

OneimportantfactorinavoidingRTOoverrunaccidentsisforthecrewtorecognizereachingV1whentheairplanedoes,infact,reachV1—notafter. The airplane’s stopping performancecannot match that specified in the Airplane FlightManualiftheassumptionsusedtoderivethatperformanceareviolated,knowinglyorinadvertently.Operationally,carefulattentiontoproceduresand teamworkare required tomatchthehumanperformancerecognizedbytheAFM.

Basicoperatingprocedurescall for thepilotflying the airplane to include airspeed in his instrumentscanduringthetakeoffgroundroll.Henceheisalwaysawareoftheapproximatespeed. The pilot not flying monitors airspeed inmoredetailandcallsout“VeeOne”asaconfirmation of reaching this critical point in theacceleration.

The pilot flying cannot react properly to V1unlesstheV1callismadeinatimely,crisp,andaudiblemanner.OnemethodofaccomplishingthisbyamajorU.S.carrieristheiradoptionofapolicyof“completingtheV1calloutbythetimetheairplanereachesV1.”ThisisanexcellentexampleofthewayairlinesareimplementingprocedurestoimproveRTOsafety.Itisagoodprocedure and it shouldpreclude a situationwherethe“NoGo”decisionisinadvertentlymadeafterV1.However,thesuccessofsuchapolicy in reducingRTOsafterV1,withoutunduly compromising the continued takeoffsafety margins, hinges on the line pilot’sunderstanding of the specific airplane model’s performancelimitationsandcapabilities.

AnotherproposalforcallingV1istouseacallsuchas“ApproachingV1”withtheV1portionoccurringastheairspeedreachesV1.Eitheroftheseproposalsaccomplishthetaskofadvisingthe flying pilot that the airplane is close to the speedwhereanRTOforallbutthemostseriousfailuresisnotrecommended.

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AfrequentlycitedfactorinRTOaccidentsthatoccurred when the First Officer was flying is the lackofanyairspeedcallsbytheCaptainduringthetakeoff.Thistypeofpoorcrewcoordinationmay be overcome by the use of automated“V1” and “Engine Failure” calls which willeliminatemuchofthevariabilityexperiencedintoday’soperations.Evenwithanautomatedcall system however, an “Approaching” callby the non-flying pilot would still seem to be an appropriate method of ensuring airspeedsituationalawarenessforbothpilots.

2.3.6.10 Crew Preparedness

Important crew factors directly related toeliminating RTO overrun accidents andincidentsare:

- BriefthosephysicalconditionswhichmightaffectanRTOthatareuniquetoeach specific takeoff.

- Bothpilotsmustbesuretopositiontheseatandrudderpedalssothatmaximumbrakepressurecanbeapplied.

- BothpilotsshouldmaintainsituationalawarenessoftheproximitytoV1.

- Usestandardcalloutsduringthetakeoff.

- Transitionquicklytostoppingconfiguration.

- Don’tchangeyourmind.IfyouhavebegunanRTO,stop.IfyouhavereachedV1,go,unlessthepilothasreasontoconcludethattheairplaneisunsafeorunable to fly.

- Usemaximumeffortbrakeapplication.

- Assuredeploymentofspeedbrakes.

- Usemaximumreversethrustallowable.

Theaccidentrecordsfrequentlyshowthatslowor incompletecrewactionwas thecauseof,orcontributedto,anRTOoverrunevent.ThecrewmustbepreparedtomaketheGo/NoGodecisiononeverytakeoff.Ifa“NoGo”decision

ismade,thecrewmustquicklyuseallofthestopping capability available. Too often, therecordsshowuncertaintyinthedecisionprocessandalackofcompletenessintheprocedures.Bereadytodecideandbereadytoact.

2.4 Crew Resource Management

CrewResourceManagement(CRM)isatermthatcanmeanmanythings.Inthiscontextitis simply intended to encompass the factorsassociatedwithhavingthecrewmembersworkeffectivelytogethertomakeoptimalGo/NoGodecisionsandeffectivelyaccomplishrelatedprocedures.ItisrecognizedthatthecontentofaCRMdiscussiononGo/NoGodecisionsmustreflect the needs and culture of each individual operator.Therefore,thematerialcontainedinthissectionisprovidedonlyasanexampleofthetypeofCRMinformationwhichcouldbeprovidedtothelinepilot.

2.4.1 CRM and the RTO

EffectiveCRMcanimprovecrewperformanceand in particular, decision making duringtakeoff.Often,Go/NoGodecisionsmustbemade “instantaneously” and as a result, thesignificance of CRM is not readily apparent. However,thefactthatacriticaldecisionmustbemadeandimplementedusingrapidlychanging,often incomplete information in a dynamicenvironment in which the time availabledecreases as the criticality of the decisionincreases,isreasonforeffectiveCRM.SomeaspectsofCRMareespeciallyimportantwithrespecttotheGo/NoGodecision.

2.4.2 The Takeoff Briefing

Crewmembersmustknowwhat isexpectedofthemandfromothers.Foroptimumcreweffectiveness, they should share a commonperception — a mental image — of what ishappeningandwhatisplanned.ThiscommonperceptioninvolvesanumberofCRMareas:

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communications, situational awareness,workload distribution, cross-checking, andmonitoring.

Avarietyofmeansareused to achieve thiscommonperception.Thisbeginswithairlinestandardoperatingpolicies(SOPs)thatclearlydefine captain and first officer as well as pilot flying and pilot not flying responsibilities and duties.Trainingreinforcesthecrew’sknowledgeand skill, while standardization insuresacceptable,consistentperformance,acrossallfleets and cultures within an airline.

A takeoff briefing is another means ofimprovingthecrew’sawareness,knowledge,and team effectiveness, especially whenspecial circumstances or conditions exist.The briefing is not necessarily a one-way process. In fact, asking for clarification or confirmation is an excellent way to insure mutualunderstandingwhenrequired.Asimple,“standard procedures” takeoff briefing might be improved by adding “I’m not perfect, sobackmeupon the speedbrakes andmyuseoftheRTOautobrakes”or,“ifwe’renotsureofanenginefailure5knotsbeforeV1,we’llcontinuethetakeoffandI’llstate‘CONTINUETAKEOFF”’. These briefings can improve team effectivenessandunderstandingoftheGo/NoGodecisionplanningandcommunicationstobeused.Suchadditionsmightbe especiallyappropriate on the first segment of a flight with a relatively new first officer or a crew’s first flight of the month.

Areviewofactionsforablowntire,highspeedconfiguration warning, or transfer of control are examples of what might be appropriatefor before takeoff (or before engine start)review. Such a briefing should address items thatcouldaffectthistakeoff,suchasrunwaycontamination, hazardous terrain or specialdeparture procedures. The briefing should not beameaninglessrepetitionofknownfacts,butratheratoolforimprovingteamperformance,that addresses the specific factors appropriate tothattakeoff.

2.4.3 Callouts

Meaningful communication, however brief,regarding a non-normal situation duringtakeoffandRTOcanoftenmeanthedifferencebetweensuccessanddisaster.Forthisreason,communications must be precise, effective,and efficient. Standard callouts contribute to improvedsituationalawareness.Thesecallouts,coupled with all crewmembers being awareofairspeed,maximize theopportunity foracommon understanding of what actions areproperintheeventofanon-normalsituation.The crewmember noting a problem shouldcommunicate clearly and precisely withoutinferring things that may not be true. Forexample, the loss of fuel flow indication alone doesnotnecessarilymeananenginefailure.Use of standard terms and phraseology todescribe the situation is essential. The pilottaskedtomaketheRTOdecisionshouldclearlyannouncethisdecision,whetheritbetocontinueorreject.

2.4.4 The Use of All Crew Members

It’s important to understand that all crewmembers on the flight deck play an important role in the Go/No Go decision and RTOmaneuver. Company policies shape theseroles.However,howtheteamisorganizedforeach takeoff can make a difference in teamperformance.Knowingyourowncapabilitiesandthatoftheothercrewmembersispartofsituational awareness and shouldbeused inplanningforagiventakeoff.Althoughit’s“thefirst officer’s leg”, it might not be an effective plan to task an inexperienced first officer with amarginalweathertakeoffwhenweightisalsolimited by field length. Consider the possibility ofanRTOwhenassigningtakeoffduties.

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2.4.5 Summary

Each airline approaches CRM in a slightlydifferent manner, but the goal of effectiveteamworkremainsthesame.ThismaterialisanexampleofthetypeofCRMinformationthatcouldbeusedtopromoteacommonperceptionofRTOproblemsandactions.

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