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

Section Page

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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

2.ii

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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

2

SECTION

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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

SECTION

2


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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

SECTION 2

2.4


8/45

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

SECTION

2


9/45

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

2.6


10/45

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

SECTION

2


11/45

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.

SECTION 2

2.8


12/45

!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


13/45

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.

SECTION 2

2.10


14/45

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

SECTION

2.


15/45

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

SECTION 2

2.12


16/45

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

2.


17/45

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

SECTION 2

2.14


18/45

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

2.


19/45

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

SECTION 2

2.16


20/45

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

SECTION

2.


21/45

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

SECTION 2

2.18


22/45


23/45

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.

SECTION 2

2.20


24/45

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

SECTION

2.


25/45

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.

SECTION 2

2.22


26/45

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

SECTION

2.


27/45

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.

SECTION 2

2.24


28/45

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.

SECTION

2.


29/45

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

SECTION 2

2.26


30/45

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

SECTION

2.


31/45

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

SECTION 2

2.28


32/45

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

SECTION

2.


33/45

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

takeoff safety

Documents