takeoff safety
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2.0 Introduction................................................................................................................... 2.1
2.1 Objectives...................................................................................................................... 2.1
2.2 SuccessfulVersusUnsuccessfulGo/NoGoDecisions.............................................. 2.1
2.2.1 AnIn-servicePerspectiveOnGo/NoGoDecisions.................................................2.2
2.2.2 SuccessfulGo/NoGoDecisions........................................................................... 2.3
2.2.3 RTOOverrunAccidentsandIncidents..................................................................... 2.4
2.2.4 Statistics.................................................................................................................... 2.5
2.2.5 LessonsLearned....................................................................................................... 2.6
2.3 DecisionsandProceduresWhat Every Pilot Should Know....................................... 2.7
2.3.1 TheTakeoffRules The Source of the Data........................................................... 2.8
2.3.1.1 TheFARTakeoffFieldLength........................................................................2.8
2.3.1.2 V1 Speed Dened.................................................................................................... 2.10
2.3.1.3 Balanced Field Dened..................................................................................... 2.11
2.3.1.4 (NotUsed).........................................................................................................2.12
2.3.2 Transition to the Stopping Conguration............................................................... 2.12
2.3.2.1 FlightTestTransitions....................................................................................... 2.12
2.3.2.2 AirplaneFlightManualTransitionTimes......................................................... 2.12
2.3.3 ComparingtheStopandGoMargins.............................................................. 2.14
2.3.3.1 TheStopMargins........................................................................................... 2.15
2.3.3.2 TheGoOption............................................................................................... 2.16
2.3.4 OperationalTakeoffCalculations........................................................................... 2.18
2.3.4.1 TheFieldLengthLimitWeight.........................................................................2.18
2.3.4.2 ActualWeightLessThanLimitWeight............................................................ 2.19
2.3.5 FactorsthatAffectTakeoffandRTOPerformance.................................................2.19
2.3.5.1 RunwaySurfaceCondition............................................................................... 2.202.3.5.1.1 Hydroplaning............................................................................................... 2.21
2.3.5.1.2 TheFinalStop.............................................................................................. 2.22
2.3.5.2 AtmosphericConditions.................................................................................... 2.22
2.3.5.3 Airplane Conguration...................................................................................... 2.23
2.3.5.3.1 Flaps.............................................................................................................. 2.23
2.3.5.3.2 EngineBleedAir.......................................................................................... 2.23
2.3.5.3.3 MissingorInoperativeEquipment.............................................................. 2.23
Pilot Guide to Takeo SaetyTable of Contents
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2.3.5.3.4 Wheels,Tires,andBrakes............................................................................ 2.25
2.3.5.3.5 WornBrakes.................................................................................................2.27
2.3.5.3.6 ResidualBrakeEnergy.................................................................................2.282.3.5.3.7 SpeedbrakeEffectonWheelBraking...........................................................2.28
2.3.5.3.8 CarbonandSteelBrakeDifferences............................................................2.30
2.3.5.3.9 HighBrakeEnergyRTOs.............................................................................2.31
2.3.5.4 ReverseThrustEffects...................................................................................... 2.32
2.3.5.5 RunwayParameters........................................................................................... 2.33
2.3.5.6 (NotUsed).........................................................................................................2.34
2.3.5.7 TakeoffsUsingReducedThrust........................................................................2.34
2.3.5.8 TheTakeoffDatathePilotSees........................................................................2.34
2.3.6 IncreasingtheRTOSafetyMargins........................................................................2.35
2.3.6.1 RunwaySurfaceCondition...............................................................................2.35
2.3.6.2 FlapSelection.................................................................................................... 2.35
2.3.6.3 RunwayLineup.................................................................................................2.36
2.3.6.4 SettingTakeoffThrust....................................................................................... 2.36
2.3.6.5 ManualBrakingTechniques.............................................................................. 2.37
2.3.6.6 AntiskidInoperativeBrakingTechniques.........................................................2.38
2.3.6.7 RTOAutobrakes................................................................................................2.38
2.3.6.8 (NotUsed).........................................................................................................2.39
2.3.6.9 TheV1Call........................................................................................................ 2.39
2.3.6.10 CrewPreparedness............................................................................................ 2.40
2.4 CrewResourceManagement...................................................................................... 2.40
2.4.1 CRMandtheRTO.................................................................................................2.40
2.4.2 The Takeoff Brieng............................................................................................... 2.40
2.4.3 Callouts................................................................................................................... 2.41
2.4.4 TheUseofAllCrewMembers............................................................................... 2.41
2.4.5 Summary.................................................................................................................2.42
Section Page
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2.0 Introduction
The Pilot Guide to Takeoff Safety is one
partoftheTakeoff Safety Training Aid.Theother
partsincludetheTakeoffSafetyOverviewfor
Management (Section 1), Example Takeoff
SafetyTrainingProgram(Section3),Takeoff
SafetyBackgroundData(Section4),andan
optionalvideo.Thesubsectionnumberingused
inSections2and4areidenticaltofacilitate
crossreferencing.Thosesubsectionsnotused
inSection2arenotednotused.
The goalofthetrainingaidisto reducethe
numberofRTOrelatedaccidentsbyimproving
the pilots decision making and associated
proceduralaccomplishmentthroughincreased
knowledge and awareness of the factors
affectingthesuccessfuloutcomeoftheGo/No
Godecision.
T he e du ca ti o na l m at er ia l a nd t he
recommendations provided in the Takeoff
Safety Training Aidweredevelopedthroughan
extensivereviewprocesstoachieveconsensusoftheairtransportindustry.
2 .1 Objectives
The objective of the Pilot Guide to Takeoff
Safetyistosummarizeandcommunicatekey
RTO related information relevant to ight
crews.Itisintendedtobeprovidedtopilots
duringacademictrainingandtoberetained
forfutureuse.
2.2 Successul Versus Unsuccessul Go/
No Go Decisions
Any Go/No Go decision can be considered
successfulifitdoesnotresultininjuryor
airplanedamage.However,justbecauseitwas
successful by this denition, it does not mean
theactionwasthebestthatcouldhavebeen
taken.Thepurposeofthissectionistopoint
outsomeofthelessonsthathavebeenlearned
throughtheRTOexperiencesofotherairline
crewssincethe1950s,andtorecommendways
ofavoidingsimilarexperiencesbythepilotsof
todays airline eet.
Pilot Guide to Takeo Saety
Takeoffs, RTOs, and Overruns
Through 2003 Typical Recent Year
Takeoffs 430,000,000 18,000,000
RTOs (est.)
RTO OverrunAccidents/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 1
Takeoffs, RTO
and Overrun
Statistics
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2.2.1 An In-service Perspective On Go/No Go
Decisions
Modern jet transport services began in the
early 1950s and signicantly increased later
thatdecadeafterintroductionoftheBoeing707 and the Douglas DC-8. As shown in
Figure 1, the western built jet transport eet
has accumulated approximately 430 million
takeoffsbytheendof2003.Recentlytherehave
beennearly18milliontakeoffsinatypicalyear.
Thatsapproximately34takeoffseveryminute,
everyday!
Since no comprehensive eet-wide records
are available, it is difcult to identify the total
numberofRTOsthathaveoccurredthroughout
the jet era. However, based onthose eventswhichhavebeendocumented,ourbestestimate
isthatonein3,000takeoffattemptsendswith
anRTO.Atthisrate,therewillbenearly6000
RTOsduringatypicalyear.Thatmeansthat
every day, 16 ight crews will perform an RTO.
Statistically,attherateofoneRTOper3000
takeoffs, a pilot who ies short haul routes and
makes80departurespermonth,willexperience
one RTO every three years. At the opposite
extreme,thelonghaulpilotmakingonlyeight
departurespermonthwillbefacedwithonly
oneRTOevery30years.
Theprobabilitythatapilotwilleverberequired
toperformanRTOfromhighspeediseven
less,asisshowninFigure2.
Availabledataindicatesthatover75%ofall
RTOsareinitiatedatspeedsof80knotsorless.TheseRTOsalmostneverresultinanaccident.
Inherently,lowspeedRTOsaresaferandless
demandingthanhighspeedRTOs.Attheother
extreme,about2%oftheRTOsareinitiated
atspeedsabove120knots.Overrunaccidents
andincidentsthatoccurprincipallystemfrom
thesehighspeedevents.
What should all these statistics tell a pilot?
First,RTOsarenotaverycommonevent.This
speakswellofequipmentreliabilityandthe
preparationthatgoesintooperatingjettransportairplanes.Bothare,nodoubt,dueinlargepart
to the certication and operational standards
developedbytheaviationcommunityovermany
yearsofoperation.Second,andmoreimportant,
the infrequencyof RTO events may lead to
complacencyaboutmaintainingsharpdecision
makingskillsandproceduraleffectiveness.In
spiteoftheequipmentreliability, every pilot
must be prepared to make the correct Go/No
Go decision on every takeoff-just in case.
SECTION 2
2.2
Figure 2
Distribution of
RTO Initiation
Speeds
KNOTSORLESS
TOKNOTS
TOKNOTS
!BOVEKNOTS
0ERCENTOFTOTAL
24/OVERRUNACCIDENTSPRINCIPALLYCOMEFROMTHEOFTHE24/STHATAREHIGHSPEED
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2.2.2 Successul Go/No Go Decisions
AswasmentionedatthebeginningofSection
2.2,thereismoretoagoodGo/NoGodecision
thanthefactthatitmaynothaveresultedin
anyapparentinjuryoraircraftdamage.Thefollowing examples illustrate a variety of
situationsthathavebeenencounteredinthe
past, some of which would t the description
ofagooddecision,andsomewhichare,at
least,questionable.
Listedatthebeginningofeachofthefollowing
examplesistheprimarycauseorcuewhich
promptedthecrewtorejectthetakeoff:
1.TakeoffWarningHorn:Thetakeoff
warninghornsoundedasthetakeoffroll
commenced.Thetakeoffwasrejected
at5knots.Theaircraftwastaxiedoff
theactiverunwaywherethecaptain
discoveredthestabilizertrimwasset
attheaftendofthegreenband.The
stabilizerwasresetandasecondtakeoff
was completed without further difculty.
2.TakeoffWarningHorn:Thetakeoffwas
rejectedat90knotswhenthetakeoff
warninghornsounded.Thecrewfound
thespeedbrakeleverslightlyoutof
thedetent.Anormaltakeoffwasmadefollowingadelayforbrakecooling.
3.EnginePowerSetting:Thethrottleswere
advancedandN1increasedtoslightly
over95%.N1eventuallystabilized
at94.8%N1.ThetargetN1fromthe
FMCTakeoffPagewas96.8%N1.The
throttles were then moved to the rewall
buttheN1stayedat94.8%.Thetakeoff
wasrejectedduetolowN1at80knots.
4.CompressorStall:Thetakeoffwasrejectedfrom155knotsduetoabird
strikeandsubsequentcompressorstall
onthenumberthreeengine.Mostofthe
tires subsequently deated due to melted
fuseplugs.
5.NoseGearShimmy:Thecrewrejected
thetakeoffafterexperiencinganose
landinggearshimmy.Airspeedatthe
timewasapproximatelyVl-10knots.All
fourmaingeartiressubsequentlyblew
during the stop, and res at the number 3
and 4 tires were extinguished by the redepartment.
6.BlownTire:Thetakeoffwasrejectedat
140knotsduetoablownnumber3main
geartire.Number4tireblewturning
ontothetaxiwaycausingthelossofboth
AandBhydraulicsystemsaswellas
major damage to aps, spar, and spoilers.
Theseexamplesdemonstratethediversityof
rejectedtakeoffcauses.AlloftheseRTOswere
successful, butsome situationscame very
close to ending differently. By contrast, the
largenumberoftakeoffsthataresuccessfully
continuedwithindicationsofairplanesystem
problemssuchascautionlightsthatilluminate
at high speed or tires that fail near V1, are
rarely ever reported outside the airlines
own information system. They may result
indiversionsanddelaysbutthelandingsare
normally uneventful, and can be completed
usingstandardprocedures.
This should not be construed as a blanket
recommendationtoGo,nomatterwhat.The
goalofthistrainingaidistoeliminateRTO
accidentsbyreducingthenumberofimproper
decisionsthataremade,andtoensurethatthe
correct procedures are accomplished when
anRTOisnecessary.Itisrecognizedthatthe
kindofsituationsthatoccurinlineoperations
are not always the simple problem that the
pilot was exposed to in training. Inevitably,
the resolution of some situations will only
be possiblethrough the good judgment and
discretion of the pilot, as is exemplied in the
followingtakeoffevent:
After selecting EPR mode toset takeoff
thrust,therightthrustleverstuckat1.21
EPR,whiletheleftthrustlevermovedto
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thetargetEPRof1.34.Thecaptaintriedto
rejectthetakeoffbuttherightthrustlever
couldnotbe movedto idle.Becausethe
lightweightaircraftwasacceleratingvery
rapidly,theCaptainadvancedthethruston
theleftengineandcontinuedthe takeoff.The right engine was subsequently shut
down during the approach, and the ight
wasconcludedwithanuneventfulsingle
enginelanding.
Thefailurethatthiscrewexperiencedwasnot
astandardtrainingscenario.Norisitincluded
heretoencouragepilotstochangetheirmind
inthemiddleofanRTOprocedure.Itissimply
anacknowledgmentofthekindofrealworld
decisionmakingsituationsthatpilotsface.Itis
perhapsmoretypicalofthegoodjudgementsthatairlinecrewsregularlymake,buttheworld
rarelyhearsabout.
2.2.3 RTO Overrun Accidents and Incidents
Theone-in-one-thousandRTOsthatbecame
accidents or serious incidents are the ones
thatwemuststrivetoprevent.Asshownin
Figure3,attheendof2003,recordsshow57in-
serviceRTOoverrunaccidentsforthewestern
built jet transport eet. These 57 accidentscausedmorethan400fatalities.Anadditional
40 serious incidents have been identied which
likelywouldhavebeenaccidentsiftherunway
overrun areas had been less forgiving. The
following are brief accounts of four actual
accidents.Theyarerealevents.Hopefully,they
willnotberepeated.
ACCIDENT: At 154k nots,four knots after
V1,thecopilotssidewindowopened,andthe
takeoff was rejected. The aircraft overran,
hittingablastfence,tearingopentheleftwing
and catching re.
ACCIDENT:Thetakeoffwasrejectedbythe
captain when the rst ofcer had difculty
maintainingrunwaytrackingalongthe7,000
footwetrunway.Initialreportsindicatethattheairplanehadslowlyacceleratedatthestartof
thetakeoffrollduetoadelayinsettingtakeoff
thrust. The cockpit voice recorder (CVR)
readoutindicatestherewerenospeedcallouts
made during the takeoff attempt. The reject
speedwas5knotsaboveV1.Thetransitionto
stoppingwasslowerthanexpected.Thiswas
to have been the last ight in a long day for the
crew.Bothpilotswererelativelyinexperienced
intheirrespectivepositions.Thecaptainhad
about140hoursasacaptaininthisairplanetype and the rst ofcer was conducting
0
5
10
1960 1965 1970 1975 1980
Year
1985 1990 1995 2000
Numberof eventsper year
Figure 3
97 RTO overrun
accidents/incidents
1959-2003
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his rst non-supervised line takeoff in this
airplanetype.Theairplanewasdestroyedwhen
it overranthe end of the runwayand broke
apartagainstpierswhichextendofftheend
oftherunwayintotheriver.Thereweretwo
fatalities. Subsequent investigation revealedthattherudderwastrimmedfullleftpriorto
thetakeoffattempt.
ACCIDE NT: A fl ock o f s ea g u ll s was
encountered very near V1. The airplane
reportedlyhadbeguntorotate.Thenumber
one engine surged and amed out, and the
takeoff was rejected. The airplane overran
theendofthewet6,000footrunwaydespitea
goodRTOeffort.
ACCIDENT: At 120 knots, the ight crew noted
theonsetofavibration.Whenthevibration
increased, the captain elected to reject and
assumedcontrol.Fourtoeightsecondselapsed
between the point where the vibration was rst
notedandwhentheRTOwasinitiated(just
afterV1).Subsequentinvestigationshowedtwo
tireshadfailed.Themaximumspeedreached
was158knots.Theairplaneoverrantheendof
the runway at a speed of 35 knots and nally
stoppedwiththenoseinaswamp.Theairplanewasdestroyed.
Thesefourcasesaretypicalofthe97reported
accidentsandincidents.
2.2.4 Statistics
Studies of the previously mentioned 97
accidents/incidents have revealed some
interestingstatistics,asshowninFigure4:
Fifty-ve percent were initiated at speeds
inexcessofV1.
Approximatelyonethirdwerereportedas
havingoccurredonrunwaysthatwerewet
orcontaminatedwithsnoworice.
Both of these issues will be thoroughly
discussedinsubsequentsections.
An additional, vitally interesting statistic
t h at w a s o bs e r ve d w he n t h e a c ci de nt
records involving Go/NoGo decisions were
reviewed, was that virtually no revenue
flight was found where a Go decision
was made and the airplane was incapable
ofcontinuing the takeoff. Regardless ofthe
abilitytosafelycontinuethetakeoff,aswillbe
seeninSection2.3,virtuallyanytakeoffcanbe
successfullyrejected,iftherejectisinitiated
earlyenoughandisconductedproperly.There
ismoretotheGo/NoGodecisionthanStop
beforeV1andGoafterV1.Thestatisticsof
thepastthreedecadesshowthatanumberof
jettransportshaveexperiencedcircumstances
nearV1thatrenderedtheairplaneincapableof
beingstoppedontherunwayremaining.Italso Figure 4Major factors
in previous RT
incidents and
accidents
)CESNOW
$RY
.OTREPORTED
7ET
'REATERTHAN6
.OT
REPORTED
,ESSTHAN
EQUALTO6
24/)NITIATION3PEED
2UNWAY#ONDITION
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mustberecognizedthatcatastrophicsituations
couldoccurwhichrendertheairplaneincapable
of ight.
Reasons why the 97 unsuccessful RTOs
wereinitiatedarealsoofinterest.Asshownin Figure 5, approximately one-fth were
initiatedbecauseofenginefailuresorengine
indicationwarnings.Theremainingseventy-
nine percent were initiated for a variety of
reasonswhichincludedtirefailures,procedural
error,malfunctionindicationorlights,noises
and vibrations, directional control difculties
andunbalancedloadingsituationswherethe
airplanefailedtorotate.Someoftheevents
containedmultiplefactorssuchasanRTOon
acontaminatedrunwayfollowinganenginefailureataspeedinexcessofV1.Thefactthat
the majority of the accidents and incidents
occurred on airplanes that had full thrust
available should gure heavily in future Go/No
Gotraining.
2.2.5 Lessons Learned
Several lessons can be learned from these
RTO accidents. First, the crew mustalways
beprepared tomaketheGo/NoGodecision
prior to the airplane reaching V1 speed. Aswill be shown in subsequent sections, there
maynotbeenoughrunwaylefttosuccessfully
stoptheairplaneiftherejectisinitiatedafter
V1.Second,inordertoeliminateunnecessary
RTOs, the crew must differentiate between
situationsthataredetrimentaltoasafetakeoff,
andthosethatarenot.Third,thecrewmustbe
preparedtoactasawellcoordinatedteam.A
goodsummarizingstatementoftheselessons
is, as speed approaches V1, the successful
completion of an RTO becomes increasingly
more difcult.
A fourth and nal lesson learned from past
RTOhistoryisillustratedinFigure6.Analysis
of the available data suggeststhatof the 97
Figure 5
Reasons for
initiating the RTO
(97 accidents/
incident events)
/THERANDNOTREPORTED
"IRDSTRIKE
#REWCOORDINATION
)NDICATORLIGHT
#ONFIGURATION
7HEELTIRE
%NGINE
0ERCENTOFTOTALEVENTS
)NCLUDINGEVENTS.OTREPORTED
!4#
.ON%NGINE
%NGINE
SECTION 2
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RTOaccidentsandincidents,approximately
82% were potentially avoidable through
appropriate operational practices. These
potentiallyavoidableaccidentscanbedivided
intothreecategories.Roughly15%oftheRTO
accidentsofthepastweretheresultofimproperpreight planning. Some of these instances
werecausedbyloadingerrorsandothersby
incorrect preight procedures. About 15% of
theaccidentsandincidentscouldbeattributed
toincorrectpilottechniquesorproceduresin
thestoppingeffort.Delayedapplicationofthe
brakes,failuretodeploythespeedbrakes,and
thefailuretomakeamaximumeffortstopuntil
lateintheRTOwerethechiefcharacteristics
ofthiscategory.
Reviewofthedatafromthe97RTOaccidentsandincidentssuggeststhatinapproximately
52%oftheevents,theairplanewascapableof
continuingthetakeoffandeitherlandingatthe
departureairportordivertingtoanalternate.In
otherwords,thedecisiontorejectthetakeoff
appears to have been improper. It is not
possible,however,topredictwithtotalcertainty
whatwouldhavehappenedineveryeventifthe
takeoffhadbeencontinued.Norisitpossible
fortheanalystoftheaccidentdatatovisualize
theeventsleadinguptoaparticularaccident
throughtheeyesofthecrew,includingalltheotherfactorsthatwerevyingfortheirattention
at the moment when the proper decision
could have been made. It is not very difcult
toimagineasetofcircumstanceswherethe
onlylogicalthingforthepilottodoistoreject
the takeoff. Encountering a large ock of birds
atrotationspeed,whichthenproduceslossof
thr ustonbothenginesofatwoengineairplane,
isaclearexample.
Althoughtheseareallvalidpoints,debating
them here will not move us any closer tothe goal of reducing the number of RTO
accidents.Severalindustrygroupshaverecently
studied this problem.Their conclusions and
recommendationsagreesurprisinglywell.The
areas identied as most in need of attention are
decision making and prociency in correctly
performingtheappropriateprocedures.These
are the same areas highlighted in Figure 6.
It would appear then, that an opportunity
exists to signicantly reduce the number of
RTOaccidentsinthefuturebyattemptingto
improvethepilotsdecisionmakingcapabilityandprocedureaccomplishmentthroughbetter
training.
2.3 Decisions and Procedures
What Every Pilot Should Know
Therearemanythingsthatmayultimatelyaffect
theoutcomeofaGo/NoGodecision.Thegoalof
theTakeoffSafetyTrainingAidistoreducethe
numberofRTOrelatedaccidentsandincidents
byimprovingthepilotsdecisionmakingandassociatedprocedureaccomplishmentthrough
increased knowledge and awareness of the
related factors. This section discusses the
rules that dene takeoff performance limit
weightsandthemarginsthatexistwhenthe
actual takeoff weight of the airplane isless
Figure 6
82% of the RTO
accidents and
incidents were
avoidable
"YBETTERPREFLIGHTPLANNING
5NAVOIDABLE
"YCONTINUINGTHETAKEOFF
"YCORRECTSTOPTECHNIQUES
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thanthelimitweight.Theeffectsofrunway
surfacecondition,atmosphericconditions,and
airplane conguration variables on Go/No Go
performancearediscussed,aswellaswhatthe
pilotcandotomakethebestuseofanyexcess
availablerunway.
Although the information contained in this
section has been reviewed by many major
airframe manufacturers and airlines, the
incorporationofanyoftherecommendations
madeinthissectionissubjecttotheapproval
ofeachoperatorsmanagement.
2.3.1 The Takeo Rules
The Source of the Data
It isimportant that all pilots understand the
takeoff eld length/weight limit rules and the
marginstheserulesprovide.Misunderstanding
therulesandtheirapplicationtotheoperational
situation could contribute to an incorrect
Go/NoGodecision.
TheU.S.FederalAviationRegulations(FARs)
have continually been rened so that the details
oftherulesthatareappliedtooneairplane
model may differ from another. However,
thesedifferencesareminorandhavenoeffect
on the basic actions required of the ight
crewduringthetakeoff.Ingeneral,itismore
importantforthecrewtounderstandthebasic
principlesratherthanthetechnicalvariations
in certication policies.
2.3.1.1 The FAR Takeo Field Length
TheFARTakeoffFieldLengthdetermined
from the FAA Approved Airplane Flight
Manual(AFM)considersthemostlimitingof
eachofthefollowingthreecriteria:
1)All-EngineGoDistance:115%ofthe
actualdistancerequiredtoaccelerate,
liftoffandreachapoint35feetabove
therunwaywithallenginesoperating
(Figure7).
2)Engine-OutAccelerate-GoDistance:
Thedistancerequiredtoacceleratewith
allenginesoperating,haveoneengine
failatVEFatleastonesecondbeforeV1,
continuethetakeoff,liftoffandreacha
point35feetabovetherunwaysurfaceatV2speed(Figure8).
3)Accelerate-StopDistance:Thedistance
requiredtoacceleratewithallengines
operating,haveanenginefailureor
othereventatVEVENTatleastone
secondbeforeV1,recognizetheevent,
recongure for stopping and bring
theairplanetoastopusingmaximum
wheelbrakingwiththespeedbrakes
extended.Reversethrustisnotused
todeterminetheFARaccelerate-stopdistance(Figure9),exceptforthewet
runway case for airplanes certied under
FARAmendment25-92.
FAR criteria provide accountability for
wind, runway slope, clearway and stopway.
FAAapprovedtakeoffdataarebasedonthe
performance demonstrated ona smooth,dry
runway. Recent models certied according to
FARAmendment25-92alsohaveapproveddata
basedonwet,andwetskid-resistantrunways.
Separateadvisorydataforwet,ifrequired,orcontaminatedrunwayconditionsarepublished
inthemanufacturersoperationaldocuments.
Thesedocumentsareusedbymanyoperators
toderivewetorcontaminatedrunwaytakeoff
adjustments..
Other criteria dene the performance weight
limitsfortakeoffclimb,obstacleclearance,tire
speedsandmaximumbrakeenergycapability.
Anyoftheseothercriteriacanbethelimiting
factorwhichdeterminesthemaximumdispatchweight.However,theFieldLengthLimitWeight
andtheamountofrunwayremainingatV1will
be the primar y focus ofour discussionhere
sincetheymoredirectlyrelatetopreventing
RTOoverruns.
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!CTUAL$ISTANCE
TIMESTHEACTUALDISTANCE
sFEET
s6TOKNOTS
sFEET
s6
SECONDMINIMUM
6%&
62
6,/&
6
24/TRANSITION
COMPLETE!&-6%6%.4
6
4RANSITION 3TOPSECONDMINIMUM
2UNWAYUSEDTOACCELERATETO6
TYPICALLY
2UNWAYAVAILABLETO'O.O'O
TYPICALLY
SECTION
2
Figure 7
All-engine go
distance
Figure 8
Engine-out
accelerate-go
distance
Figure 9
Accelerate-stop
distance
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2.3.1.2 V1 Speed Defned
V1
Whatistheproperoperationalmeaningofthe
keyparameterV1speedwithregardtothe
Go/NoGocriteria?Thisisnotsuchaneasy
questionsincethetermV1speedhasbeen
redened several times since commercial jet
operationsbeganmorethan30yearsagoand
thereispossibleambiguityintheinterpretation
of the words used to dene V1.
Paragraph 25.107 of the FAA Regulations
denes the relationship of the takeoff speedspublishedin the Airplane Flight Manual, to
various speeds determined in the certication
testingoftheairplane.Forourpurposeshere,
the most important statement within this
ofcial denition is that V1isdeterminedfrom
...the pilots initiation of the rst action to stop
the airplane during the accelerate-stop tests.
Onecommonandmisleadingwaytothinkof
V1istosayV1isthedecisionspeed.Thisis
misleadingbecauseV1isnotthepointtobeginmakingtheoperationalGo/NoGodecision.The
decision must have been made by the time the
airplane reaches V1orthepilotwillnothave
initiatedtheRTOprocedureatV1.Therefore,
by denition, the airplane will be traveling at
aspeedhigherthanV1whenstoppingaction
is initiated, and if the airplane isat a Field
LengthLimitWeight,anoverrunisvirtually
assured.
Anothercommonlyheldmisconception:V1is
theenginefailurerecognitionspeed,suggests
thatthedecisiontorejectthetakeofffollowing
enginefailurerecognitionmaybeginaslateas
V1.Again,theairplanewillhaveacceleratedto
aspeedhigherthanVIbeforestoppingaction
isinitiated.
The certied accelerate-stop distance calculation
isbasedonanenginefailureatleastonesecond
prior to V1. This standard time allowance1
has been established to allow the line pilot
torecognizeanenginefailureandbeginthe
subsequentsequenceofstoppingactions.
InanoperationalFieldLengthLimitedcontext,
the correct denition of V1 consists of two
separateconcepts:First,withrespecttotheNoGocriteria,
V1 is the maximum speed at which
the rejected takeoff maneuver can
be initiated and the airplane stopped
within the remaining eld length under
the conditions and procedures dened
1ThetimeintervalbetweenVEFandVl is the longer of the ight test demonstrated time or one second. Therefore, in determiningthescheduledaccelerate-stopperformance,onesecondistheminimumtimethatwillexistbetweentheenginefailureandtherst pilot stopping action.
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in the FARs. It is the latest point in
the takeoff roll where a stop can be
initiated.
Second,withrespecttotheGocriteria,
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. Thisaspect
ofV1isdiscussedinalatersection.
TheGo/NoGodecisionmustbemadebefore
reachingV1.A No Go decision after passing
V1will not leave sufcient runway remaining
to stop if the takeoff weight is equal to the
Field Length Limit Weight.Whentheairplane
actual weight is less than the Field Length
Limit Weight, it is possible to calculate theactualmaximumspeedfromwhichthetakeoff
couldbesuccessfullyrejected.However,few
operatorsusesuchtakeoffdatapresentations.
Itisthereforerecommendedthatpilotsconsider
V1tobealimitspeed:DonotattemptanRTO
once the airplane has passed V1 unless the
pilot has reason to conclude the airplane is
unsafe or unable to y. This recommendation
should prevail no matter what runway length
appears to remain after V1.
2.3.1.3 Balanced Field Defned
The previous two sections established the
general relationship between the takeoff
performance regulations and V1speed.This
sectionprovidesacloserexaminationofhow
thechoiceofV1actuallyaffectsthetakeoff
performance in specic situations.
Sinceitisgenerallyeasiertochangetheweight
ofanairplanethanitistochangethelengthofarunway,thediscussionherewillconsider
theeffectofV1ontheallowabletakeoffweight
from a xed runway length.
The Continued TakeoffAfter an engine
failure during the takeoff roll, the airplane
mustcontinuetoaccelerateontheremaining
engine(s),liftoffandreachV2speedat35feet.
Thelater in the takeoff roll that the engine
fails,theheaviertheairplanecanbeandstill
gainenoughspeedtomeetthisrequirement.
Fortheenginefailureoccurringapproximately
onesecondpriortoV1,therelationshipofthe
allowableengine-outgotakeoffweighttoV1
wouldbeasshownbytheContinuedTakeoff
lineinFigure10.ThehighertheV1,theheavier
thetakeoffweightallowed.
TheRejectedTakeoff Onthestopsideofthe
equation,theV1/weighttradehastheopposite
trend.The lowertheV1,orthe earlierinthe
takeoffrollthestopisinitiated,theheavierthe
airplanecanbe,asindicatedbytheRejected
TakeofflineinFigure10.
ThepointatwhichtheContinuedandRejected
Takeofflinesintersectisofspecialinterest.It
denes what is called a Balanced Field Limit
Figure 10
Effect of V1 sp
on takeoff weig
(from a xed
runway length)
Continuedtakeoff
Rejectedtakeoff
Airplaneweight
V speed1
Increasing
Increasing
Field limit weight
Balancedfield
LimitV
speed
1
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takeoff.ThenameBalancedFieldrefersto
the fact that the accelerate-go performance
required is exactly equal to (or balances)
the accelerate-stop performance required.
FromFigure10itcanalsobeseenthatatthe
Balanced Field point, the allowable FieldLimitTakeoffWeightforthegivenrunwayis
themaximum.Theresultinguniquevalueof
V1isreferredtoastheBalancedFieldLimit
V1Speedandtheassociatedtakeoffweight
iscalledthe BalancedFieldWeightLimit.
This is the speed that is typically given to ight
crewsinhandbooksorcharts,bytheonboard
computersystems,orbydispatch.
2.3.1.4 (Not Used)
2.3.2 Transition to the Stopping Confguration
In establishing the certied accelerate-stop
distance, the time required to recongure the
airplane from the Go tothe Stop mode
is referred to as the transition segment.
T h is act io n and t he ass ociated t i me of
accomplishmentincludesapplyingmaximum
brak ing simultaneously moving the thr ust
levers to idle and raising the speedbrakes.The transition time demonstrated by ight
test pilots during the accelerate-stop testing
isusedtoderivethetransitionsegmenttimes
usedintheAFMcalculations.Therelationship
between the ight test demonstrated transition
times and those nally used in the AFM is
anotherfrequentlymisunderstoodareaofRTO
performance.
2.3.2.1 Flight Test Transitions
Several methods of certication testing that
producecomparableresultshavebeenfoundto
beacceptable.Thefollowingexampleillustrates
theintentofthesemethods.
During certication testing the airplane is
acceleratedtoapre-selectedspeed,oneengine
isfailed by selecting fuel cut off,and the
pilot ying rejects the takeoff. In human
factors circles, this is dened as a simple task
becausethetestpilotknowsinadvancethatan
RTOwillbeperformed.Exactmeasurements
of the time taken by the pilot to apply thebrakes,retardthethrust leverstoidle,andto
deploythespeedbrakesarerecorded.Detailed
measurements of engine parameters during
spooldown are also made so that the thrust
actuallybeinggeneratedcanbeaccountedfor
inthecalculation.
The manufacturers test pilots, and pilots
from the regulatory agency, each perform
severalrejectedtakeofftestruns.Anaverage
of the recorded data from at least six of
these RTOs is then used to determine thedemonstrated transition times. The total ight
testdemonstratedtransitiontime,initialbrake
applicationtospeedbrakesup,istypicallyone
secondorless.Howeverthisisnotthetotal
transition time used to establish the certied
accelerate-stop distances. The certication
regulationsrequirethatadditionaltimedelays,
sometimesreferredtoaspads,beincludedin
the calculation of certied takeoff distances.
2.3.2.2 Airplane Flight Manual TransitionTimes
Althoughthelinepilotmustbepreparedfor
anRTOduringeverytakeoff,itisfairlylikely
thattheeventorfailurepromptingtheGo/No
Godecisionwillbemuchlessclear-cutthan
anoutrightenginefailure.Itmaythereforebe
unrealistictoexpecttheaveragelinepilotto
performthetransitioninaslittleasonesecond
inanoperationalenvironment.Humanfactors
literature describes the line pilots job as acomplextasksincethepilotdoesnotknow
whenanRTOwilloccur.Inconsiderationof
this complex task, the ight test transition
times are increased to calculate the certied
accelerate-stop distances specied 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.Their
purpose is to allow sufcient time (and distance)
fortheaveragepilottotransitionfromthe
takeoffmodetothestoppingmode.
The rst adjustment is made to the time required
torecognizetheneedtostop.DuringtheRTO
certication ight testing, the pilot knows
thathewillbedoinganRTO.Therefore,his
reactionispredictablyquick.Toaccountfor
this,aneventrecognitiontimeofatleastone
secondhasbeensetasastandardforalljet
transport certications since the late 1960s.
V1 istherefore, atleastonesecondafterthe
event.Duringthisrecognitiontimesegment,
theairplanecontinuestoacceleratewiththe
operatingengine(s)continuingtoprovidefull
forward thrust. If the event was an engine
failure,thefailedenginehasbeguntospool
down,butitisstillprovidingsomeforward
thrust,addingtotheairplanesacceleration.
Overtheyears,thedetailsofestablishingthe
transitiontimesegmentsafterV1havevaried
slightlybuttheoverallconceptandtheresulting
transitiondistanceshaveremainedessentially
thesame.Forearlyjettransportmodels,an
additionalonesecondwasaddedtoboththe
ight test demonstrated throttles-to-idle time
and the speedbrakes-up time, as illustrated
in Figure 11. The net result is that the ighttest demonstratedrecognitionand transition
time of approximately one secondhas been
increased for the purpose of calculating the
AFMtransitiondistance.
In more recent certication programs, the AFM
calculation procedure was slightly different.
Anallowanceequaltothedistancetraveled
duringtwosecondsatthespeedbrakes-upspeed
wasaddedtotheactualtotaltransitiontime
demonstrated in the ight test to apply brakes,bringthethrust leversto idleand deploythe
speedbrakes,asshowninFigure12.Toinsure
consistentandrepeatableresults,retardation
forces resulting from brake application and
speed brake deployment are not applied
duringthistwosecondallowancetime,i.e.no
decelerationcreditistaken.Thistwosecond
distance allowance simplies the transition
distancecalculationandaccomplishesthesame
goalastheindividualonesecondpadsused
Figure 11
Early method o
establishing AF
transition time
!&-TRANSITION
COMPLETE
&LIGHTTEST
%NGINE
&AILURE
!&-EXPANSION
&LIGHTTESTDEMONSTRATEDTRANSITIONTIME
!&-TRANSITIONTIME
!&-SECOND
MINIMUM
SEC SEC
2ECOGNITION
6
"RAKE
SON
4HROTTLESTOIDLE
3PEEDBRAKES
SECTION
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foroldermodels.
Evenmorerecently,FARAmendments25-42
and25-92haverevisedthewayinwhichthe
twoseconddistanceallowanceiscalculated.
Regardlessofthemethodused,theaccelerate-stopdistancecalculatedforeverytakeofffrom
theAFMistypically400to600feetlongerthan
the ight test accelerate-stop distance.
Thesedifferencesbetweenthepastandpresent
methodology are not signicant in so far as
the operational accelerate-stop distance is
concerned.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,thepads
provideanallowancethatassuresthepilothasadequatedistancetogettheairplaneintothe
full stopping conguration.
Regardlessoftheairplanemodel,thetransition,
or reconguring of the airplane for a rejected
takeoff,demandsquickactionbythecrewto
simultaneously initiate maximum braking,
retardthethrustleverstoidleandthenquickly
raisethespeedbrakes.
2.3.3 Comparing the Stop and GoMargins
WhenperformingatakeoffataFieldLength
LimitWeightdeterminedfromtheAFM,the
pilotisassuredthattheairplaneperformance
w il l, a t t he m i ni mu m , c on fo rm t o t he
requirementsoftheFARsiftheassumptions
ofthecalculationsaremet.Thismeansthat
followinganenginefailureoreventatV EVENT,
thetakeoffcanberejectedatV1andtheairplane
stoppedattheendoftherunway,orifthetakeoff
iscontinued,aminimumheightof35feetwillbereachedovertheendoftherunway.
Thissectiondiscussestheinherentconservatism
of these certied calculations, and the margins
they provide beyond the required minimum
performance.
Figure 12
More recent
method of
establishing AFM
transition time
!&-TRANSITION
COMPLETE
&LIGHTTEST
!&-EXPANSION
&LIGHTTESTDEMONSTRATEDTRANSITIONTIME
!&-TRANSITIONTIME
!&-SECONDMINIMUM
&4DEMO
SEC
2ECOGNITION
6
"RAKESO
N
4HRO
TTLESTOID
LE
3PEED
BRAKES
3ERVICEALLOWANCE
%VENT
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2.3.3.1 The Stop Margins
F ro m t he p re c ed i ng d is cu s si on of t he
certication rules, it has been shown that at
a Field Length Limit Weight condition, an
RTOinitiatedatV1willresultintheairplanecomingtoastopattheendoftherunway.This
accelerate-stop distance calculation species an
enginefailureoreventatVEVENT,thepilots
initiationoftheRTOatV1,andthecompletion
ofthetransitionwithinthetimeallottedinthe
AFM.Ifanyofthesebasicassumptionsarenot
satised, the actual accelerate-stop distance
mayexceedtheAFMcalculateddistance,and
anoverrunwillresult.
The most signicant factor in these assumptions
istheinitiationoftheRTOnolaterthanV1.Yetaswasnotedpreviously,inapproximately
55%oftheRTOaccidentsthestopwasinitiated
afterV1.AtheavyweightsnearV1,theairplane
istypically travelingat 200 to 300 feet per
second,andacceleratingat3to6knotsper
second. This means that a delay of only a
secondortwoininitiatingtheRTOwillrequire
severalhundredfeetofadditionalrunwayto
successfullycompletethestop.Ifthetakeoff
wasataFieldLimitWeight,andthereisno
excessrunwayavailable,theairplanewillreach
the end of the runway at a signicant speed, asshowninFigure13.
The horizontal axis of Figure 13 is the
incrementalspeedinknotsaboveV1atwhich
amaximum effortstopisinitiated.Thevertical
axisshowstheminimum speedinknotsatwhich
theairplanewouldcrosstheendoftherunway,
assuming the pilotusedall of the transitiontime allowed in the AFM to recongure the
airplane to the stop conguration, and that a
maximumstoppingeffortwasmaintained.The
datainFigure13assumesanenginefailurenot
lessthanonesecondpriortoV1anddoesnot
includetheuseofreversethrust.Therefore,if
thepilotperformsthetransitionmorequickly
thantheAFMallottedtime,and/orusesreverse
thrust,thelinelabeledMAXIMUMEFFORT
STOPwouldbeshiftedslightlytotheright.
However,basedontheRTOaccidentsofthe
past,theshadedareaabovethelineshowswhatismorelikelytooccurifahighspeedRTOis
initiatedatorjustafterV1.Thisisespeciallytrue
iftheRTOwasduetosomethingotherthanan
enginefailure,orifthestoppingcapabilityof
theairplaneisotherwisedegradedbyrunway
surface contamination, tire failures, or poor
technique.ThedatainFigure13aretypicalofa
large,heavyjettransportandwouldberotated
slightlytotherightforthesameairplaneata
lighterweight.
In the nal analysis, although the certied
accelerate-stopdistance calculationsprovide
Figure 13
Overrun Speed
an RTO initiat
after V1
!BORTINITIATIONSPEEDABOVESCHEDULED6
KNOTS
-AXIMU
MEFFORT
STOP
3PEEDOFFENDOF
RUNWAYKNOTS
3HADEDAREAINDICATESDEGRADED
STOPPINGPERFORMANCE
s#ONTAMINATEDRUNWAY
s0ILOTTECHNIQUE
s3YSTEMFAILURES
SECTION
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sufcient runway for a properly performed
RTO,theavailablemarginsarefairlysmall.
Most importantly, there are no margins to
accountforinitiationoftheRTOafterV1or
extenuating circumstances such as runway
contamination.
2.3.3.2 The Go Option
FARrulesalsoprescribeminimumperformance
standardsfortheGosituation.Withanengine
failedatthemostcriticalpointalongthetakeoff
path,theFARGocriteria requiresthatthe
airplanebeabletocontinuetoaccelerate,rotate,
liftoffandreachV2speedatapoint35feetabove
theendoftherunway.Theairplanemustremaincontrollablethroughoutthismaneuverandmust
meet certain minimum climb requirements.
These handling characteristics and climb
requirements are demonstrated many times
throughout the certication ight test program.
Whileagreatdealofattentionisfocusedon
theenginefailurecase,itisimportanttokeep
inmind,thatin over three quarters of all RTO
accident cases, full takeoff power was available.
Itislikelythateachcrewmemberhashada
good deal of practice in engine inoperativetakeoffsinpriorsimulatororairplanetraining.
However,itmayhavebeendoneatrelatively
lighttrainingweights.Asaresult,thecrewmay
conclude that large control inputs and rapid
responsetypicalofconditionsnearminimum
controlspeeds(Vmcg)arealwaysrequiredin
ordertomaintaindirectionalcontrol.However,
at the V1 speeds associated with a typical
FieldLengthLimitWeight,thecontrolinput
requirementsarenoticeablylessthantheyare
atlighterweights.
Also, at light gross weights, the airplanes
rate of climb capability with one-engine
inoperativecouldnearlyequaltheall-engine
climb performance at typical in-service
weights, leading the crew to expect higher
performancethantheairplanewillhaveifthe
actualairplaneweightisatornearthetakeoff
ClimbLimitWeight.Engine-outrateofclimb
andaccelerationcapabilityataClimbLimit
Weightmayappeartobesubstantiallylessthan
thecrewanticipatesorisfamiliarwith.
Theminimumsecondsegmentclimbgradients
required in the regulations vary from 2.4%
to3.0%dependingonthenumberofengines
installed. These minimum climb gradients
translateintoaclimbrateofonly350to500
feetperminuteatactualclimblimitweights
andtheirassociatedV2speeds,asshownin
Figure 14. The takeoff weight computations
performed prior to takeoff are required to
account for all obstacles in the takeoff ightpath . All that is required to achieve the
anticipated ight path is adherence by the ight
crewtotheplannedheadingsandspeedsper
their pre-departure brieng.
Consider a one-engine-inoperative case
wherethe enginefailure occurs earlier than
the minimum time before V1 specied in
therules.Becauseengine-outaccelerationis
less than all-engine acceleration, additional
distance is needed to accelerate to VR and,as a consequence, the liftoff point will be
movedfurtherdowntherunway.Thealtitude
(orscreenheight)achievedattheendofthe
runway is somewhat reduced depending on
howmuchmorethanonesecondbeforeV1the
engine failure occurs. On a eld length limit
runway,theheightattheendoftherunway
may be less than the 35 feet specied in the
regulations.
Figure 15 graphically summarizes thisdiscussion of Go margins. First, let VEF
be the speed at which the Airplane Flight
Manualcalculationassumestheenginetofail,
(a minimum of one second before reaching
V1).ThehorizontalaxisofFigure15shows
the number of knots prior to VEF that the
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engineactuallyfailsinsteadofthetime,and
the vertical axis gives the screen height
achievedattheendoftherunway.Atypical
rangeofaccelerationforjettransportsis3to6
knotspersecond,sotheshadedareashowsthe
rangeinscreenheightthatmightoccurifthe
engineactuallyfailedonesecondearly,or
approximatelytwosecondspriortoV 1.Inother
words,aGodecisionmadewiththeengine
failureoccurringtwosecondspriortoV1will
resultinascreenheightof15to30feetfora
FieldLengthLimitWeighttakeoff.
Figure15alsoshowsthattheGoperformance
margins are strongly inuenced by the number
ofengines.Thisisagaintheresultofthelarger
proportionofthrustlosswhenoneenginefails
on the two-engine airplane compared to a
-20 -16 -12 -8 -4 0
0
10
20
30
40
(35)
(150)
One-engine inoperative
All engines
2-eng
ineairplane
Height at end
of runway, ft
Speed at actual engine failurerelative to VEF, knots
V2 + 10 to 25 knots
V2
+8+4
TypicalV1 range
One secondminimum
4-engineairpla
ne
3-engineairp
lane
&0-AT6^KNOTS
&0-AT6^KNOTS
&0-AT6^KNOTS
-INIMUMGRADIENTREQUIRED
ENGINE
ENGINE
ENGINE
4YPICALRATEOFCLIMB
DEGREEBANKTURNWILLREDUCETHESE
CLIMBRATESBYAPPROXIMATELY&0-
Figure 14
GO perfoma
at climb limit
weights
Figure 15
Effect of engin
failure before V
on screen heigh
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threeorfour-engineairplane.Ontwo-engine
airplanes,therearestillmargins,buttheyare
notaslarge,afactthatanoperatorofseveral
airplanetypesmustbesuretoemphasizein
trainingandtransitionprograms.
It should also be kept in mind that the 15
to 30 foot screen heights in the preceding
discussion were based on the complete loss
ofthrustfromoneengine.Ifallenginesare
operating, as was the case in most of the
RTOaccidentcases,theheightovertheend
of the Field Length Limit runway will be
approximately 150 feet and speed will be
V2+10 to 25 knots, depending on airplane
type.Thisisduetothehigheraccelerationand
climbgradientprovidedwhenallenginesareoperatingandbecausetherequiredallengine
takeoffdistanceismultipliedby115%.Ifthe
failed engine is developing partial power,
the performance is somewhere in between,
but denitely above the required engine-out
limits.
2.3.4 Operational Takeo Calculations
As we have seen, the certication ight testing,inaccordancewiththeappropriategovernment
regulations, determines the relationship
between the takeoff gross weight and the
requiredrunwaylengthwhichispublishedinthe
AFM.ByusingthedataintheAFMitisthen
possibletodetermine,foragivencombination
ofambientconditionsandairplaneweight,the
required runway length which will comply
with the regulations. Operational takeoff
calculations,however,haveanadditionaland
obviouslydifferentlimitation.Thelengthof
therunwayistheLimitFieldLengthanditisxed, not variable.
2.3.4.1 The Field Length Limit Weight
Instead of solving for the required runway
length, the rst step in an operational takeoff
calculation is to determine the maximum
airplane weight which meets the rules forthe xed runway length available. In other
words,whatisthelimitweightatwhichthe
airplane:
1)Willachieve35-ftaltitudewithall
enginesoperatingandamarginof15%
oftheactualdistanceusedremaining;
2)Willachieve35-ftaltitudewiththe
criticalenginefailedonesecondprior
toV1;
3)WillstopwithanenginefailureorothereventpriortoV1andtherejectinitiated
atV1;
all within the existing runway length
available.
Theresultofthiscalculationisthreeallowable
weights.Thesethreeweightsmayormaynotbe
thesame,butthelowestofthethreebecomesthe
FieldLengthLimitWeightforthattakeoff.
Aninterestingobservationcanbemadeatthispointas to whichof these three criteria will
typically determine the Takeoff Field Limit
Weightforagivenairplanetype.Two-engine
airplanesloseone-halftheirtotalthrustwhen
anenginefails.Asaresult,theFieldLength
LimitWeightfortwo-engineairplanesisusually
determinedbyoneoftheengine-outdistance
criteria.Ifitislimitedbytheaccelerate-stop
distance,therewillbesomemargininboth
theall-engineandaccelerate-godistances.If
thelimitistheaccelerate-godistance,some
marginwouldbeavailablefortheall-enginegoandaccelerate-stopcases.
By comparison, four-engine airplanes only
loseone-fourthoftheirtakeoffthrustwhenan
enginefailssotheyarerarelylimitedbyengine-
outgoperformance.TheFieldLengthLimit
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2.3.5.1 Runway Surace Condition
Theconditionoftherunwaysurfacecanhave
a signicant effect on takeoff performance,
sinceit canaffect both the acceleration and
deceleration capability of the airplane. Theactualsurfaceconditioncanvaryfromperfectly
drytoadamp,wet,heavyrain,snow,orslush
coveredrunwayinaveryshorttime.Theentire
lengthoftherunwaymaynothavethesame
stoppingpotentialduetoavarietyoffactors.
Obviously, a 10,000-ft runway with the rst
7,000feetbareanddry,butthelast3,000feet
asheetofice,doesnotpresentaverygood
situationforahighspeedRTO.Ontheother
hand, there are also specially constructed
runways with a grooved or Porous Friction
Coat(PFC)surfacewhichcanofferimprovedbrakingunderadverseconditions.Thecrews
cannotcontroltheweatherliketheycanthe
airplanes conguration or thrust. Therefore, to
maximizeboththeGoandStopmargins,
theymustrely on judiciously applying their
companyswetorcontaminatedrunwaypolicies
aswellastheirownunderstandingofhowthe
performanceoftheirairplanemaybeaffected
byaparticularrunwaysurfacecondition.
The certication testing is performed on a
smooth,ungrooved,dryrunway.Forairplanes
certied under FAR Amendment 25-92, testing
isalsoperformedonsmoothandgroovedwet
runways.Anycontaminationnotcoveredinthe
certication data which reduces the availablefrictionbetweenthetireandtherunwaysurface
willincreasetherequiredstoppingdistancefor
anRTO.Runwaycontaminantssuchasslush
orstandingwatercanalsoaffectthecontinued
takeoff performance due to displacement
and impingement drag associated with the
spray from the tires striking the airplane.
Somemanufacturersprovideadvisorydatafor
adjustmentoftakeoffweightand/orV1when
the runway is wet or contaminated. Many
operators use this data to provide ight crews
withamethodofdeterminingthelimitweights
forslipperyrunways.
Factorsthatmakearunwayslipperyandhow
theyaffectthestoppingmaneuverarediscussed
inthefollowingsections.
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2.3.5.1.1 Hydroplaning
Hydroplaning is an interesting subject since
mostpilotshaveeitherheardoforexperienced
instancesofextremelypoorbrakingactiononwetrunwaysduringlanding.Thephenomenon
ishighlysensitivetospeedwhichmakesitan
especially important consideration for RTO
situations.
Asatirerollsonawetrunway,itsforward
motiontendstodisplacewaterfromthetread
contactarea.Whilethisisntanyproblemat
lowspeeds,athighspeedsthisdisplacement
action can generate water pressures sufcient
toliftandseparatepartofthetirecontactarea
fromtherunwaysurface.Theresultingtire-to-groundfrictioncanbeverylowathighspeeds
butfortunatelyimprovesasspeeddecreases.
Dynamic hydroplaning is the term used to
describe the reduction of tire tread contact
areaduetoinducedwaterpressure.Athigh
speeds on runways with signicant water,
theforwardmotionofthewheelgeneratesa
wedgeofhighpressurewaterattheleading
edgeofthecontactarea,asshowninFigure
16A.Dependingonthespeed,depthofwater,
andcertaintireparameters,theportionofthetiretreadthatcanmaintaincontactwiththe
runway varies signicantly. As the tread contact
areaisreduced,theavailablebrakingfriction
isalsoreduced.Thisisthepredominantfactor
leading to reduced friction onr unways that
have either slush, standing water or signicant
waterdepthduetoheavyrainactivity.Inthe
extremecase,totaldynamichydroplaningcan
occurwherethetiretorunwaycontactarea
vanishes,thetireliftsofftherunwayandrides
onthewedgeofwaterlikeawaterski.Sincetheconditionsrequiredtoinitiateandsustain
total dynamic hydroplaning are unusual, it
is rarely encountered. When it does occur,
suchasduringanextremelyheavyrainstorm,
it virtually eliminates any tire braking or
corneringcapabilityathighspeeds.
Another form of hydroplaning can occur
where there is some tread contact with the
runwaysurfacebutthewheeliseitherlocked
or rotating slowly (compared to the actual
airplane speed). The friction produced bytheskiddingtirecausesthetreadmaterialto
becomeextremelyhot.AsindicatedinFigure
16B,theresultingheatgeneratessteaminthe
contactareawhichtendstoprovideadditional
upwardpressureonthetire.Thehotsteamalso
startsreversingthevulcanizingprocessused
in manufacturing the rubber tread material.
The affected surface tread rubber becomes
irregularinappearance,somewhatgummyin
nature,andusuallyhasalightgraycolor.This
revertedrubberhydroplaningresultsinvery
lowfrictionlevels,approximatelyequaltoicyrunwayfrictionwhenthetemperatureisnear
themeltingpoint.Anoccurrenceofreverted
rubberhydroplaningisrareandusuallyresults
fromsomekindofantiskidsystemorbrake
malfunctionwhichpreventedthewheelfrom
rotatingattheproperspeed.
Figure 16A
Dynamic Hydroplaning
Figure 16B
Reverted Rubber Hydroplaning
&LOODEDRUNWAY,OCKEDTIRE
3TREAMPRESSURE
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In the last several years, many runways
throughout the world have been grooved,
thereby greatly improving the potential wet
runway friction capability. As a result, the
numberofhydroplaningincidentshasdecreased
considerably.Flighttestsofonemanufacturersairplane on a well maintained grooved
runway,whichwasthoroughlydrenchedwith
water,showedthatthestoppingforceswere
approximately90%oftheforcesthatcouldbe
developedonadryrunway.Continuedefforts
togrooveadditionalrunwaysortheuseofother
equivalenttreatmentssuchasporousfriction
overlays, will signicantly enhance the overall
safetyoftakeoffoperations.
Theimportantthingtorememberaboutwet
orcontaminatedrunwayconditionsisthatforsmoothrunwaysurfacesthereisapronounced
effect of forward ground speed on friction
capability,aggravatedbythedepthofwater.
Forproperlymaintainedgroovedorspecially
treated surfaces, the friction capability is
markedlyimproved.
2.3.5.1.2 The Final Stop
Areviewofoverrunaccidentsindicatesthat,in
manycases,thestoppingcapabilityavailablewas not used to the maximum during the
initialandmidportionsofthestopmaneuver,
becausethereappearedtobeplentyofrunway
available.Insomecases,lessthanfullreverse
thrustwasusedandthebrakeswerereleasedfor
aperiodoftime,lettingtheairplanerollonthe
portionoftherunwaythatwouldhaveproduced
goodbrakingaction.Whentheairplanemoved
onto the nal portion of the runway, the crew
discoveredthatthepresenceofmoistureonthe
topofrubberdepositsinthetouchdownand
turnoff areas resulted in very poor brakingcapability,andtheairplanecouldnotbestopped
ontherunway.WhenanRTOisinitiatedonwet
orslipperyrunways,itisespeciallyimportant
tousefullstoppingcapabilityuntiltheairplane
iscompletelystopped.
2.3.5.2 Atmospheric Conditions
Ingeneral,theliftthewingsgenerateandthrust
theenginesproducearedirectlyrelatedtothe
airplanesspeedthroughtheairandthedensity
of that air. The ight crew should anticipatethattheairplanestakeoffperformancewillbe
affectedbywindspeedanddirectionaswell
astheatmosphericconditionswhichdetermine
airdensity.Properlyaccountingforlastminute
changesinthesefactorsiscrucialtoasuccessful
Go/NoGodecision.
Theeffectofthewindspeedanddirectionon
takeoffdistanceisverystraightforward.Atany
givenairspeed,a10-knotheadwindcomponent
lowersthe groundspeed by 10 knots. Since
V1, rotation, and liftoff speeds are at lower
groundspeeds,therequiredtakeoffdistance
isreduced.Theoppositeoccursifthewind
hasa10-knottailwindcomponent,producing
a10-knotincreaseinthegroundspeed.The
requiredrunwaylengthisincreased,especially
thedistancerequiredtostoptheairplanefrom
V1. Typical takeoff data supplied to the ight
crew by their operations department will
eitherprovidetakeoffweightadjustmentstobe
appliedtoazerowindlimitweightorseparate
columns of limit weights for specic values
of wind component. In either case, it isthe
responsibility of the ight crew to verify that
lastminutechangesinthetowerreportedwinds
areincludedintheirtakeoffplanning.
Theeffectofairdensityontakeoffperformance
isalsostraightforwardinsofarasthecrew
isnormallyprovidedthelatestmeteorological
informationpriortotakeoff.However,itisthe
responsibilityofthecrewtoverifythecorrect
pressurealtitudeandtemperaturevaluesusedin determining the nal takeoff limit weight
andthrustsetting.
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2.3.5.3 Airplane Confguration
The planned conguration of the airplane at the
timeoftakeoffmustbetakenintoconsideration
by the ight crew during their takeoff planning.
This should include the usual things like apselection, and engine bleed conguration, as
well as the unusual things like inoperative
equipmentcoveredbytheMinimumEquipment
List (MEL) or missing items as covered by
the Conguration Deviation List (CDL). This
sectionwilldiscusstheeffectoftheairplanes
conguration on takeoff performance capability
and/or the procedures the ight crew would use
tocompleteorrejectthetakeoff.
2.3.5.3.1 Flaps
The airplanes takeoff eld length performance
is affected by ap setting in a fairly obvious way.
Foragivenrunwaylengthandairplaneweight,
thetakeoffspeedsarereducedbyselectinga
greater ap setting. This is because the lift
required for ight is produced at a lower V2
speed with the greater ap deection. Since the
airplanewillreachtheassociatedlowerV1speed
earlierinthetakeoffroll,therewillbemore
runwayremainingforapossiblestopmaneuver.OntheGosideofthedecision,increasing
the takeoff ap deection will increase the
airplanedrag and the resulting lower climb
performance maylimittheallowabletakeoff
weight.However,thetakeoffanalysisusedby
the ight crew will advise them if climb or
obstacleclearanceisalimitingfactorwitha
greater ap setting.
2.3.5.3.2 Engine Bleed Air
Wheneverbleedairisextractedfromanengine,
andthevalueofthethrustsettingparameter
isappropriatelyreduced,theamountofthrust
theenginegeneratesisreduced.Therefore,theuseofenginebleedairforairconditioning/
pressurizationreducestheairplanespotential
takeoffperformanceforagivensetofrunway
length,temperatureandaltitudeconditions.
When required, using engine and/or wing
anti-ice further decreases the performance
onsomeairplanemodels.Thislostthrust
may be recoverable via increased takeoff
EPRorN1limitsasindicatedintheairplane
operatingmanual.Itdependsonenginetype,
airplane model, and the specic atmospheric
conditions.
2.3.5.3.3 Missing or Inoperative Equipment
In op erat i ve o r mi s si n g eq ui pment can
sometimes affect the airplanes acceleration
or deceleration capability. Items which
are allowed to be missing per the certied
Conguration Deviation List (CDL), such
asaccesspanelsandaerodynamicseals,cancauseairplanedragtoincrease.Theresulting
decrements tothe takeoff limit weightsare,
when appropriate, published in the CDL.
Withthesedecrementsapplied,theairplanes
takeoffperformancewillbewithintherequired
distancesandclimbrates.
Inoperativeequipmentordeactivatedsystems,
aspermittedundertheMinimumEquipment
List (MEL) can also affect the airplanes
dispatched Go or Stop performance.
For instance, on some airplane models, aninoperative in-ight wheel braking system may
requirethe landing gear tobe left extended
during a large portion of the climbout to
allow the wheels tostoprotating.The Go
performancecalculationsfordispatchmustbe
made in accordance with certied Landing
GearDownFlightManualdata.Theresulting
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new limit takeoff weight may be much less
thantheoriginallimitinordertomeetobstacle
clearance requirements, and there would be
someexcessrunwayavailableforarejected
takeoff.
AnMELitemthatwouldnotaffecttheGo
performance margins but would denitely
degradetheStopmarginsisaninoperative
anti-skidsystem.Inthisinstance,notonlyisthe
limitweightreducedbytheamountdetermined
from the AFM data, but the ight crew may also
berequiredtouseadifferentrejectedtakeoff
procedure in which throttles are retarded rst,
the speedbrakes deployed second, and then
thebrakesareappliedinajudiciousmannerto
avoidlockingthewheelsandfailingthetires.3
TheassociateddecrementintheFieldLength
LimitWeightisusuallysubstantial.
OtherMELitemssuchasadeactivatedbrake
may impact both the continued takeoff and
RTOperformancethroughdegradedbraking
capability and loss of in-ight braking of the
spinningtire.
The ight crew should bear in mind that
the performance of the airplane with these
typesofCDLorMELitemsintheairplanes
maintenancelogatdispatchwillbewithinthe
certied limits. However, it would be prudent
for the ight crew to accept nal responsibility
toassurethattheitemsareaccountedforin
thedispatchprocess,andtoinsurethatthey,
asacrew,arepreparedtoproperlyexecuteany
revisedprocedures.
3UKCAAprocedureadds...applymaximumreversethrust.
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2.3.5.3.4 Wheels, Tires, and Brakes
The airplanes wheels, tires, and brakes are
anotherareathatshouldbeconsideredinlight
of the signicant part they play in determining
theresultsofaGo/NoGodecision.
One design featurewhich involvesall three
components is the wheel fuse plug. All jet
transportwheelsusedforbrakingincorporate
thermalfuseplugs.Thefunctionofthefuseplug
istopreventtireorwheelburstsbymeltingifthe
heattransferredtothewheelsfromthebrakes
becomes excessive. Meltingtemperatu res of
fuseplugsareselectedsothatwithexcessive
brake heat, the ination gas (usually nitrogen)
isreleased before the structural integrity of
thetireorwheelisseriouslyimpaired.Both
certification limitations and operationalrecommendationstoavoidmeltingfuseplugs
areprovidedtooperatorsbythemanufacturer,
asisdiscussedinSection2.3.5.3.6underthe
heading,ResidualBrakeEnergy.
While fuse plugs provide protection from
excessive brake heat, it isalso important to
recognizethatfuseplugscannotprotectagainst
all types of heat induced tire failures. The
locationofthefusepluginthewheelisselected
toensureproperresponsetobrakeheat.This
locationincombinationwiththeinherentlow
thermalconductivityoftirerubbermeansthat
thefuseplugscannotpreventtirefailuresfrom
therapidinternalheatbuildupassociatedwith
taxiing on an underinated tire. This type of heat
buildupcancauseabreakdownoftherubber
compound,plyseparation,and/orruptureofthe
plies.Thisdamagemightnotcauseimmediate
tirefailureandbecauseitisinternal,itmay
notbeobviousbyvisualinspection.However,
theweakenedtireismorepronetofailureona
subsequent ight. Long taxi distances especially
athighspeedsandheavytakeoffweightscanaggravatethisproblemandresultina blown
tire. While underination is a maintenance
issue, ight crews can at least minimize the
possibilityoftire failuresduetooverheating
byusinglowtaxispeedsandminimizingtaxi
brakingwheneverpossible.
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Correct tire ination and fuse plug protection
are signicant, but will never prevent all tire
failures. Foreign objects in parking areas,
taxiwaysandrunwayscancauseseverecutsin
tires.Theabrasionassociatedwithsustained
lockedorskiddingwheels,whichcanbecausedbyvariousantiskidorbrakeproblems,cangrind
throughthetirecordsuntilthetireisseverely
weakenedorablowoutoccurs.Occasionally,
wheel cracks develop which deate a tire and
generateanoverloadedconditionintheadjacent
tireonthesameaxle.Someoftheseproblemsare
inevitable.However,itcannotbeoverstressed
that proper maintenance and thorough walk
aroundinspectionsarekeyfactorsinpreventing
tirefailuresduringthetakeoffroll.
Tire failures may be difcult to identify from theight deck and the related Go/No Go decision
isthereforenotasimpletask.Atireburstmay
beloudenoughtobeconfusedwithanengine
compressorstall,mayjustbealoudnoise,or
maynotbeheard.Atirefailuremaynotbe
feltatall,maycausetheairplanetopulltoone
side,orcancausetheentireairplanetoshake
andshuddertotheextentthatinstrumentsmay
become difcult to read. Vibration arising out of
failureofanosewheeltirepotentiallypresents
anothercomplication.Duringtakeoffrotation,
vibrationmayactuallyincreaseatnosewheelliftoffduetothelossofthedampeningeffect
ofhavingthewheelincontactwiththerunway.
Apilotmustbecautiousnottoinappropriately
conclude, under such circumstances, that
anotherproblemexists.
Although continuing a takeoff with a failed
tire will generally have no signicant adverse
results,theremaybeadditionalcomplications
asaresultofatirefailure.Failedtiresdonot
inthemselvesusuallycreatedirectionalcontrol
problems.Degradation ofcontrolcan occur,
however, as a result of heavy pieces of tire
materialbeingthrownatveryhighvelocities
andcausingdamagetotheexposedstructure
of the airplane and/or the loss of hydraulic
systems. On airplanes with aft mounted
engines,thepossibilityofpiecesofthefailed
tirebeingthrownintoanenginemustalsobe
considered.
An airplanes climb gradient and obstacle
clearance performance with all engines
operatingandthelandinggeardownexceedsthe minimum certied engine-out levels that
areusedtodeterminethetakeoffperformance
limits.Therefore,leavingthegeardownafter
asuspectedtirefailurewillnotjeopardizethe
aircraftifallenginesareoperating.However,if
theperceivedtirefailureisaccompaniedbyan
indicationofthrustloss,orifanengineproblem
shoulddeveloplaterin thetakeoffsequence,
theairplanesclimbgradient and/orobstacle
clearance capability may be significantly
reducedifthelandinggearisnotretracted.The
decisiontoretractthegearwithasuspectedtireproblemshouldbeinaccordancewiththe
airlines/manufacturersrecommendations.
Ifatirefailureissuspectedatfairlylowspeeds,
it should be treated the same as any other
rejectable failure and the takeoff should be
rejectedpromptly.Whenrejectingthetakeoff
withablowntire,thecrewshouldanticipate
thatadditionaltiresmayfailduringthestop
attempt and that directional control may be
difcult. They should also be prepared for the
possiblelossofhydraulicsystemswhichmaycausespeedbrakeorthrustreverserproblems.
Sincethestoppingcapabilityoftheairplanemay
be signicantly compromised, the crew should
notrelaxfromamaximumeffortRTOuntilthe
airplaneisstoppedonthepavement.
Rejecting a takeoff from high speeds with
a failed tire is a much riskier proposition,
especiallyiftheweightisneartheFieldLimit
Weight.Thechancesofanoverrunareincreased
simplyduetothelossofbrakingforcefrom
onewheel.Ifadditionaltiresshouldfailduring
thestopattempt,theavailablebrakingforceis
evenfurtherreduced.Inthiscase,itisgenerally
bettertocontinuethetakeoff,ascanbe seen
inFigure17.Thesubsequentlandingmaytake
advantageofalowerweightandspeedifitis
possibletodumpfuel.Also,thecrewwillbe
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better prepared forpossible vibration and/or
controlproblems.Mostimportant,however,is
thefactthattheentirerunwaywillbeavailable
forthestopmaneuverinsteadofperhaps,as
littleas40%ofit.
As can be seen from this discussion, it isnot a straightforward issue to dene when a
takeoffshouldbecontinuedorrejectedafter
a suspected tire failure. It is fairly obvious
however,thatanRTOinitiatedathighspeed
withasuspectedtirefailureisnotapreferred
situation. McDonnell Douglas Corporation,
inanAllOperatorLetter4,hasaddressedthis
dilemma by recommending a policy of not
rejectingatakeoffforasuspectedtirefailure
atspeedsaboveV120 knots. The operators
of other model aircraft should contact the
manufacturer for specic recommendations
regardingtirefailures.
2.3.5.3.5 Worn Brakes
TheinvestigationofonerecentRTOincident
whichwasinitiatedverynearV1,revealed
thattheoverrunwastheresultof8ofthe10
wheel brakes failing during the RTO. The
failed brakes were later identied to have been
atadvancedstatesofwearwhich,whilewithin
acceptedlimits,didnothavethecapacityfora
highenergyRTO.
This was the rst and only known accident in
thehistoryofcommercialjettransportoperation
thatcanbetracedtofailureofthebrakesduring
anattemptedRTO.TheNationalTransportation
SafetyBoard(NTSB)investigatedtheaccident
andmadeseveralrecommendationstotheFAA.
The recommendations included the need to
requireairplaneandbrakemanufacturersto
verifybytestandanalysisthattheirbrakes,
whenworntotherecommendedlimits,meetthe certication requirements. Prior to 1991,
maximumbrakeenergylimitshadbeenderived
fromtestsdonewithnewbrakesinstalled.
Virtually all brakes in use today have wear
indicatorpinstoshowthedegreeofwearand
when the brake must be removed from the
!VAILABLE2UNWAY
3AMEINITIALCONDITIONS
s4AKEOFFFLAPS
s#ERTIFIEDPERFORMANCE
s$RYRUNWAY
s&IELDLENGTHLIMITWEIGHT
s,ANDINGFLAPS
s#ERTIFIEDPERFORMANCE
LESSBLOWNTIREEFFECTS
s4AKEOFFWEIGHTMINUS
BURNOFFANDFUELDUMPOPTFT
3TOPZONE
2EJECT
'O
6
4RANSITIONCOMPLETE
4RANSITIONCOMPLETE
62
6%&
62
6
FT
2EJECT
'O
TOKTS
TOFTOVERRUN
%NGINEFAIL
4IREFAIL
TO-ARGIN
TO
!PPROXFT
2EDUCEDBRAKINGCAPABILITYPLUSALL
ENGINEREVERSE
&ULLSTOPPINGNOREVERSE
Figure 17
Margins associ
with continuin
rejecting a tak
with a tire failu
4McDonnellDouglasAllOperatorsLette rFO-AOL-8-0 03,-9-006,-10-00 4,-11-015,Reiteration of Procedures and TechniquesRegarding Wheels, Tires, and Brakes,dated19AUG1991
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airplane.Inmostcases,asthebrakewears,the
pinmovescloserto areferencepoint,sothat
when the end of the pin is ush with the reference
(withfullpressureapplied),thebrakeisworn
out.Asoflate1991,testshavebeencompleted
whichshowthatbrakesattheallowablewearlimitcanmeetAFMbrakeenergylevels.As
a result, wear pin length is not signicant
to the ight crew unless the pin indicates that
thebrakeiswornoutandshouldberemoved
from service. There are no changes to ight
crewordispatchproceduresbasedonbrake
wearpinlength.
2.3.5.3.6 Residual Brake Energy
Afterabrakeapplication,theenergywhichthebrakehasabsorbedisreleasedasheatanduntil
thisheatisdissipated,theamountofadditional
energy which the brake can absorb without
failureisreduced.Therefore,takeoffplanning
must consider the effects of residual brake
energy(orbraketemperature)iftheprevious
landing involved signicant braking and/or the
airplaneturnaroundisrelativelyshort.There
are two primary sources of information on
thissubject.Thebraketemperaturelimitations
and/orcoolingchartsintheairplaneoperating
manualproviderecommendedinformationontemperaturelimitationsand/orcoolingtimes
and the procedures necessary to dissipate
variousamountsofbrakeenergy.Inaddition,
the Maximum Quick Turnaround Weight
(MQTW) chartin the AFM is a regulatory
requirementthatmustbefollowed.Thischart
showsthegrossweightatlandingwherethe
energy absorbed by the brakes during the
landing could be high enough to cause the
wheel fuse plugs to melt and establishes a
minimumwaiting/coolingtimeforthesecases.
TheMQTWchartassumesthattheprevious
landingwasconductedwithmaximumbraking
fortheentirestopanddidnotusereversethrust,
soformanylandingswhereonlylightbraking
wasusedthereissubstantialconservatismbuilt
intothewaitrequirement.
2.3.5.3.7 Speedbrake Eect on Wheel
Braking
Whilejettransportpilotsgenerallyunderstand
the aerodynamic drag benet of speedbrakes
andthecapabilityofwheelbrakestostopanairplane,theeffectofspeedbrakesonwheel
brakeeffectivenessduringanRTOisnotalways
appreciated. The reason speedbrakes are so
criticalistheirpronouncedeffectonwinglift.
Depending on ap setting, the net wing lift
canbe reduced, eliminated orreversed toa
downloadbyraisingthespeedbrakes,thereby
increasing the vertical load on the wheels
which in turn can greatly increase braking
capability.
Speedbrakes are important since for mostbraking situations, especially any operation
onslipperyrunways,thetorqueoutputofthe
brake,andthereforetheamountofwheelbrake
retardingforcethatcanbedevelopedishighly
dependent on the vertical wheel load. As a
result,speedbrakesmustbedeployedearlyin
thestoptomaximizethebrakingcapability.
During RTO certication ight tests, the
stoppingperformanceisobtainedwithprompt
deploymentofthespeedbrakes.Failure to raise
the speedbrakes during an RTO or raising
them late will signicantly increase thestopping distance beyond the value shown
in the AFM.
Figures 18 and 19 summarize the effect of
speedbrakes during an RTO. For a typical
mid-sizedtwo-enginetransport,atatakeoff
weightof225,000lb,thetotalloadonthemain
wheelsatbrakereleasewouldbeapproximately
193,000lb.Astheairplaneacceleratesalongthe
runway,wingliftwilldecreasetheloadonthe
gear,andbythetimetheairplaneapproaches
V1speed,(137knotsforthisexample),themain
gearloadwillhavedecreasedbynearly63,000
lb.ThedatainFigure19graphicallydepicts
howtheforcesactingontheairplanevarywith
airspeedfromafewknotsbeforetheRTOis
initiateduntiltheairplaneisstopped.Whenthe
pilotbeginstheRTObyapplyingthebrakesand
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4OTALSTOPPINGFORCECAPABILITY
INCREASE
$RAG
"RAKES
$RAG
,OADONWHEELS
,IFT
"RAKES
&ORWARDMOTION
2OLLING
"RAKETORQUE "RAKINGFORCE
"RAKINGFORCEBRAKINGFRICTIONXLOADONTIRE
"RAKETORQUENOTLIMITING
3PEEDBRAKESDOWN
3PEEDBRAKESUP
3PEEDBRAKEPOSITION
5P$OWN
$IFFERENCESPEEDBRAKEUP
$RAG
,IFT
.ETLOADONWHEELS
-AXBRAKINGFORCE
-AXSTOPPINGFORCEBRAKESANDDRAG
LBS
LBS
LBS
7EIGHTONTIRE
Figure 18
Effect of
speedbrakes on
stopping capab
of a typical mid
size two-engine
transport
Figure 19
Summary of fo
during a typica
mid-size two-
engine airplan
RTO
3PEED+4!3
2ETARDINGFORCELB
"RAKINGFORCEWITHSPEEDBRAKESUP
"RAKINGFORCEWITHSPEEDBRAKESDOWN
4WOENGINEREVERSETHRUSTFORCE
!ERODRAGWITHSPEEDBRAKESUP
!ERODRAGWITHSPEEDBRAKESDOWN
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closingthethrustlevers,thebrakingforcerises
quicklytoavalueinexcessof70,000lb.The
nearlyverticallinemadebythebrakingforce
curveinFigure19alsoshowsthattheairplane
begantodeceleratealmostimmediately,with
virtuallynofurtherincreaseinspeed.
ThenextactioninatypicalRTOprocedure
istodeploythespeedbrakes.Bythetimethis
action is completed, and the wheel brakes
havebecomefullyeffective,theairplanewill
haveslowedseveralknots.Inthisexampleof
an RTO initiatedat 137 knots,the airspeed
wouldbeabout124knotsatthispoint.The
weightonthemaingearat124knotswouldbe
approximately141,600lbwiththespeedbrakes
down,andwouldincreaseby53,200lbwhen
the speedbrakes are raised. The high speedbrakingcapabilityissubstantiallyimprovedby
this38%increaseinwheelloadfrom141,600to
194,800pounds,whichcanbeseenbynoting
theincreaseinbrakingforceto98,000pounds.
In addition, the speedbrakes have an effect
onaerodynamicdrag,increasingitby73%,
from8,500to14,700pounds.The combined
result,asindicatedbythetableinFigure18,
isthatduringthecritical,highspeedportion
oftheRTO,thetotalstoppingforceactingon
the airplane is increased by 34% when the
speedbrakesaredeployed.
Sinceboththeforcethebrakescanproduce
andtheaerodynamiceffectofthespeedbrakes