air accident investigation unit ireland
TRANSCRIPT
Air AccidentInvestigation Unit
Ireland
SeriouS incident report Airbus A330-301, ei-ord
over iceland11 May 2010
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
2
Air Accident Investigation Unit Report 2012-015
AAIU Report No: 2012-015
State File No: IRL00910032
Report Format: Synoptic Report
Published: 20/09/2012
In accordance with the provisions of SI 460 of 2009, the Chief Inspector of Air Accidents, on 12 May 2010, appointed Mr. Graham Liddy as the Investigator-in-Charge to carry out a Field Investigation into this Serious Incident and prepare a Report. Due to his retirement, on the 29 February 2012 the Chief Inspector appointed Mr. Paul Farrell as the Investigator-in-Charge to complete the Investigation. The sole purpose of this Investigation is the prevention of aviation Accidents and Incidents. It is not the purpose of the Investigation to apportion blame or liability.
Aircraft Type and Registration: Airbus A330-301, EI-ORD
No. and Type of Engines: 2 x General Electric CF6-80E1A2
Aircraft Serial Number: MSN 059
Year of Manufacture: 1994
Date and Time (UTC): 11 May 2010 @ 15.08 hrs (UTC1)
Location: Over Iceland; N64º 45.011’, W019º 20.001’
Type of Operation: Scheduled Public Transport
Persons on Board: Crew - 11 Passengers - 227
Injuries: Crew - 0 Passengers - 0
Nature of Damage: Right Hand (RH) inboard aileron, outside
servo-control, outer bracket failure2
Commander’s Licence: JAA ATPL
Commander’s Details: Male, aged 52 years
Commander’s Flying Experience: 19,200 hours, of which 4,931 were on type
Notification Source: Aircraft Operator
Information Source: AAIU Field Investigation
1 UTC:UniversalTimeCo-ordinated,whichisthesameasGreenwichMeanTime.AlltimingsquotedinthisreportareinUTC.
2 Eachwinghastwoailerons,designated“inboard”and“outboard”inthisReport.Eachaileronhastwoservo-controls,designated“inside”and“outside”
inthisReport.Eachservo-controlhastwoattachingbrackets,designated“inner”and“outer”inthisReport.Theseconventionsarenotadheredtowhen
quotingfromofficialpublications.
3
SYNOPSIS
Theaircraftwascruisingat33,000ft,whenitencounteredturbulence.Thisturbulenceresultedinamoderateun-commandedroll.
Whiletheautopilotwascorrectingthisroll,theouterbracketsupportingtheoutsideservo-controloftheRHinboardaileronfailed,causingtheRHinboardailerontooscillatequicklyfrom14degreesupwardsdeflectionto12degreesdownwardsdeflectionandsettlingatanupwardsdeflectionoftheorderof15degrees.Thisdidnotcauseanycontrolproblemsandtheautopilotwasabletocontinuetocontroltheaircraft.Theaircraftlandedwithoutdifficultyattheintendeddestination,ChicagoO’Hare(KORD).SubsequentlyacrackwasdetectedinacorrespondingbracketontheLeftHand(LH)wing.
1. FACTUAL INFORMATION
1.1 History of the Flight
TheaircraftwasonascheduledpublictransportflightfromDublin(EIDW)toKORD.Aroundthedateofthisflight,thevolcanicashsituationarisingfromtheeruptionatEyjafjallajökullinIcelandwasposingamajorproblemtoaircraftoperationsinEuropeandintheNorthAtlanticarea.Atthetimeofflight,alargecloudofvolcanicashwasstreamingdownfromIcelandinasouthwestdirection.Forthisreasontheflightwasroutedalongamorenortherlytrackthannormal,routinginitiallyfromDublintoIcelandandtheninawesterlydirectiontoKORD.DuetothefunnellingofaircrafttracksintheIcelandicarea,arisingfromthepresenceoftheashcloudtothesouthwest,therewasconsiderablecongestionintheairspaceoverIceland.AsaresultEI-ORDwasgivenacruisingaltitudeofFL330(FlightLevel330or33,000ft).TheFlightCrew,beingawareofthissituationpriortodeparturefromEIDWandtheincreasedfuelconsumptionresultingfromthislowerthannormalcruisingaltitude,andalsobecauseofthelongerrouterequiredtoavoidtheashcloud,hadtakenonextrafuel.WhileoverIceland(Figure No. 1)theaircraftencounteredsomemoderateturbulencewhichtheFlightCrewsuspectedmighthavebeencausedbywaketurbulence.Theturbulenceresultedinsomeaircraftrollandyaw.Theautopilot,whichremainedengagedduringtheturbulenceencounter,quicklyreturnedtheaircrafttolevelflight.ShortlyafterwardstheaircraftwasclearedtoclimbtoFL380.TheFlightCrewinputtedthisnewaltitudeintothealtitudeselectorandtheaircraftcommencedaclimbtothenewcruisingaltitude,undercontroloftheautopilot.Duringthisclimb,theFlightCrewobservedalowerthanexpectedrateofclimbandahigherthanexpectedfuelconsumptionrate.
4
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
Figure No. 1: Overview of aircraft location at time of event
TheFlightCrewstartedtotrouble-shootthecauseofthislossofperformance.Duringthistrouble-shootingtheyobservedthattheElectronicCentralisedAircraftMonitoring(ECAM)FlightControlpageshowedthattheRHinboardaileronwas2/3offull-scaleaboveitsnormalposition.TheRHoutboardaileronwasdeflecteddownwardsby1/3offull-scalefromitsnormalposition.BothLHaileronsweredeflectedupwardsby1/3offull-scalefromtheirnormalpositions.TherewerenoECAMwarningsorcautions.TheFlightCrewforthisparticularflightconsistedofthreepilotssotheCaptainwasabletoleavetheflightdeckandgotothecabinwhereheobtainedvisualconfirmationthatthephysicalconfigurationoftheaileronscorrespondedwiththeindicationsontheECAM.TheFlightCrewnotedthattheFlightCrewOperationManual(FCOM)gavenospecificinformationonthecauseoftheobservedproblem,butitstatedthatintheeventofanun-commandedflightcontrolsurfacedeflection,theflightcouldbecontinuedasnormalifnohandlingproblemswerenoted.TheFCOMincludedcrewawarenessguidancewhichpredictedincreasedfuelconsumptionintherange6-16%.TheFlightCrewcontactedtheOperator’smaintenancecontrolcentreinDublinviatheAircraftCommunicationsAddressingandReportingSystem (ACARS).ThepossibilityofresettingPRIM(FlightControlPrimaryComputer)2wasdiscussedbutMaintenanceControladvisedagainstthis.UsingtheHeading(HDG)selectfacility,andwithoutdisconnectingtheautopilot,theFlightCrewsatisfiedthemselvesthattheycouldsuccessfullymanoeuvretheaircraft.Thecockpitandcabinweresecured(passengersandCabinCrewseatedandstrappedin)andtheFlightCrewthenturnedofftheautopilotandverifiedthattherewerenodifficultiesinmanuallycontrollingtheaircraft.Theythenre-engagedtheautopilot,whichcontinuedcontrollingtheaircraftwithoutdifficulty.
5
AtthispointtheaircraftwastothewestofIceland.TheFlightCrewconsideredtheiroptions.Basedonthefactsthat:
• theaircraftwashandlingnormally, • theywereapproximatelyhalfwaytotheirdestination, • theyhadmorethanadequatefueltoreachtheirplanneddestinationevenallowingforthe
increasedfuelconsumption,(becauseoftheextrafuelupliftedatEIDW), • theplanneddestinationofferedalongrunway(13,000ft),whichcouldproveusefuliftheywere
toexperiencehandlingdifficultiesduringtheapproach, • areturntoEIDWatthispointwouldrequiretheaircrafttomanoeuvrearoundthevolcanicash
cloudwhichwasnowbehindthem,
theFlightCrewdecidedtoproceedtoKORD,andtheremainderoftheflightpassedwithoutfurtherincident.
OnestablishingcontactwithKORD,theFlightCrewadvisedATCthattheyhadaflightcontrolsystemsproblem,thenatureofwhichtheycouldnotdetermine.TheyrequestedanapproachtothelongestrunwayatKORD(RWY28/10)incasetheyexperiencedhandlingproblemsastheaircraft’sspeedwasreducedandtheaircraftwasreconfiguredforapproachandlanding(flapsandundercarriagedeployed).ATCqueriediftheyweredeclaringanemergencyandtheFlightCrewsaidno.ATCthendecidedthattheywouldhavetodeclareanemergency,asthiswouldensurethatRWY28/10wouldbeavailabletoEI-ORD.
TheaircraftapproachedandlandedatKORDwithoutdifficultyorincident.
1.2 Injuries to Persons
Therewerenoinjuriessustainedinthisevent.
Injuries Flight Crew Passengers Other
Fatal 0 0 0
Serious 0 0 0
Minor/None 11 227 0
6
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
1.3 Damage to the Aircraft
1.3.1 System Description
OntheA330aircrafteachwingisfittedwithtwoailerons,designatedasinboardandoutboard.Twoelectro-hydraulicservo-controls(actuator)areattachedtoeachaileron(inboardandoutboard).Innormaloperationsonlytheoutsideservo-controlactuatestheaileroninresponsetoinputsfromthecockpitsidesticksortheautopilot.Theinsideservo-controloperatesinadampingmodeandpreventsflutterintheeventofmultipleelectricalorhydraulicsystemfailures.
However,intheeventoffailureoftheoutsideservo-control,theinsideservo-controlcantakeovertheactive/commandfunction.Eachwingisalsofittedwithsixspoilerpanels,numbered1to6,theinnermostpanelbeingNo1.Rollcontrolinflightisachievedbyacombinationofmovementsofinboardandoutboardaileronsanddeploymentofspoilers2throughto6.Athigheraircraftspeeds(inthecruise)onlytheinboardaileronsareoperatedandtheoutboardaileronsareservoedtozero.Oneendoftheservo-controlisattachedtotheaileronitactuates;theotherisattachedtothewingrearsparthroughapairofbrackets(Figure No. 2).
Figure No. 2: Engineering schematic of the assembly (LH Wing)
7
1.3.2 Damage Found on Arrival
OnarrivalatKORDtheaircraftwasinspectedbymaintenancepersonnel.Thebrackets(PartNumberF575-50986)attachingtheoutside(active)servo-control,oftheRHinboardaileron,totheRHwingrearspar,werefoundtobefractured(Photo No. 1),andthelowerwingskindirectlybeneaththebrackets’attachmentpointswasdeflected.Furtherinspectionrevealedthatthecorrespondingouterbracketontheother(LH)sideoftheaircraftwascrackedinthesameareawheretheRHouterbrackethadfailed.
Photo No. 1: The fractured brackets
1.4 Other Damage
Therewasnootherdamage.
8
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
1.5 Personnel Information
1.5.1 Commander Personal Details: Male,aged52years Licence: JAAATPL,IssuedbytheIAA Last Periodic Check: 4Feb2010 Medical Certificate: Class1
Flying Experience: Total all types: 19,200 hours Total all types P1: 16,909 hours Total on type: 4,931 hours Total on type P1: 4,900 hours Last 90 days: 99 hours Last 28 days: 42 hours Last 24 hours: 9.92 hours
1.5.2 First Officer Personal Details: Male,aged35years Licence: JAAATPL,issuedbyIAA Last Periodic Check: 08Oct2009 Medical Certificate: Class1
Flying Experience: Total all types: 6,386 hours Total all types P1: 3,072 hours Total on type: 2,108 hours Last 90 days: 108 hours Last 28 days: 30 hours Last 24 hours: 9.9 hours
1.5.3 Third Pilot Personal Details: Male,aged49years Licence: JAAATPL,IssuedbytheIAA Last Periodic Check: 13Jan2010 Medical Certificate: Class1
Flying Experience: Total all types: 17,700 hours Total all types P1: 10,000 hours Total on type: 2,100 hours Total on type P1: 2,000 hours Last 90 days: 89 hours Last 28 days: 23.15 hours Last 24 hours: 9.53 hours
1.6 Meteorological Information
Theaircraftencounteredmoderateturbulenceatthestartoftheevent.
1.7 Navigation
Aidstonavigationwerenotafactorinthisevent.
9
1.8 Communications
Communicationswerenotafactorinthisevent.
1.9 Aerodrome Information KORDisamajorinternationalairport.Ithasatotalofsevenrunways,whichvaryinlengthfrom
7,500ftto13,000ft.RWY10/28is13,000ftlong,andexceedsthelengthofallotherKORDrunwaysbyatleast3,000ft.
1.10 Flight Recorders
1.10.1 Cockpit Voice Recorder (CVR)
TheaircraftwasequippedwithasolidstateCVR,whichhadarecordingdurationoftwohours.
Theeventoccurredmorethantwohoursbeforetheaircraftlanded.Consequently,therecordingatthetimeoftheeventwasnotavailableandsotheCVRwasnotofanyassistancetotheInvestigation.
1.10.2 Flight Data Recorder (FDR)
DownloadingoftheFDRprovidedthefollowinginformation:
Theaircraftwasinthecruiseat33,000ftwithAP1(Autopilot#1)andFD(FlightDirector)on;ATHR(Auto-thrust)wasengaged.
At15.08:03hrstheaircraftencounteredturbulenceandverticalloadpeaksof0.73and1.45Gwererecorded.Theaircraftimmediatelystartedtobanktotheleftatthistime.ThisrollwascounteractedbyaileronsandRHspoilers.Amaximumbankangleof11degreesleftbankwasreachedsevensecondslaterat15.08:10hrs.
Theaircraftthenstartedtorolltotheright,startingat15.08:12hrs.ThisrollwascounteractedbyaileronsandLHspoilers.TheRHinboardailerondeflectedto14degreesup.threesecondslateritwasat12degreesdownandonesecondlateritwasat13degreesup.Overthesubsequent6secondsitmovedto15degreesup.Inresponsetothisaileronmovementtheaircraftcontinuedtorolltotheright.Amaximumrightbankangleof20degreeswasrecordedat15.08:15hrs.
Thebankanglethendampedtotheleftreaching6degreesleftandrightbankandstabilisedinlevelflight(zerodegrees)at15.08:50hrs.
Inthestabilisedconditionwiththewingslevel,theinboardaileronsstabilisedatRHAileron15degreesupandLHaileron7degreesupwhiletheoutboardRHaileronstabilisedat7degreesdownandtheLHoutboardaileronat6degreesup.
At16.32:44hrstheFlightCrewdisconnectedtheautopilot.Theoutboardaileronsthenservoedtozerodegrees(thisisinaccordancewiththedesignspecificationwhentheaircraftisinthecleanconfigurationabove190kts).Theaircraftinitiallyrolledtotherightduetotheasymmetricpositionoftheinboardailerons.Thiswasmanuallycorrectedwithaleftsidestickinputof1/3deflection.RollcontrolcontinuedtobeavailablebymovementsoftheLHinboardaileronandthespoilers.
10
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
1.11 Damage Information
AfterlandingatKORDthebracketpairsupportingtheoutsideservo-controlontheRHinneraileronwasfoundtohavefailedandwasremoved.Thepaircomprisedtheoutsideservo-controlouterbracket(F575-50989)andtheoutsideservo-controlinnerbracket(F575-50987).ThebracketassemblywasdesignatedbypartnumberF575-50986.ThecorrespondingbracketassemblyontheLHwing,whichNonDestructiveTesting(NDT)foundtobecracked,wasalsoremoved.ThefailedbracketpairwasinitiallyshippedtotheOperator’sbaseatDublinandthentakenbytheAAIUtotheaircraftManufacturer’sfacilityintheUKforexamination.
TheManufacturer’sexaminationcomprised:visualexamination;NDTexamination;Fractographicanalysis;Hardnesstesting;ElectricalConductivitytesting;Mechanicalpropertiestestingofthefailedbracketsandsurfacefinishexaminationofacurrentproductionstandardbracket.
TheManufacturer’sexaminationrevealedthattheprimaryfailurewasoftheouterbracket.Thefailurewascausedbyfatiguecrackingwhichoriginatedfromapitinthebracketsurface.Thepit,whichwasapproximately50micronsindepth,wasbelievedtohavebeenpresentinthebracketsinceitwasmanufactured.Followingfailureoftheouterbracketduetofatiguecrackingtheinnerbracketfailedduetooverload.
Detailedexaminationofthewinglowerskinintheareadirectlybelowthefailedbracketrevealedanareaofdeformationbetweenribs28and29.Thedeformationstartedattheaftsparfastenerlineandcontinuedaftreachingamaximumvalueof6.9mm.(Photo No. 2)
Photo No. 2: Deformation of lower wing skin, RH wing
Therewasnodeformationofthebottomskindirectlyundertherearspar,norwasthereanydeformationoftherearsparflangefasteners,norelongationofassociatedholes.Thelowerfastenerholesintherearsparwebforattachingthebracketstotherearsparwebwerefoundtobeelongated;theholeshadaninitialdiameterof7.94mmbutwerefoundtobeelongatedto8.6mmapproximately.
Therewasnofuelleak.
1.12 Medical and Pathological Information
Therewerenomedicalorpathologicalissuesinthisevent.
1.13 Fire
Therewasnofire.
11
1.14 Survival Aspects
Therewerenosurvivalaspects/issuesinthisevent.
1.15 Test and Research
TheManufacturercarriedoutresearchasdetailedbelow.
1.16 Organisational and Management Information
Notapplicable.
1.17 Additional Information
AtthetimeofthiseventtheaircraftManufacturerinformedtheInvestigationthattherehadbeenatotalofsixeventsrelatingtofailedorcrackedbracketsonA330andA340aircraft;theA340hasasimilarwingwithidenticalbrackets.FouroftheseeventshadoccurredpriortotheEI-ORDeventandanotherhadoccurredonthesameday.Detailsofthesebracketcrack/failureeventsareshownin Appendix A.
Replacementoftheservo-controlbracketsisnotastraightforwardtask,inspiteofthefactthatthebracketswereboltedontothewingrearspar.Thisisbecausethebracketsaresuppliedwithonlypilotholesfortheattachmentboltsandtheseneedtobecustomdrilledtothefinishedsizeandlocationforthewinginquestion.
1.17.1 Manufacturer’s Service Bulletin (SB) A330-57-3109
TheManufacturerpublishedSBA330-57-3109on13February2009.ThisSBwastitled“Wings–InnerAileronRearSparOuterattachments–InspectionofOuterBrackets”.ThereasonforissuingtheSBwasthat“anoperatorreportedcracksonbothbracketsattachingtheLHActiveServocontrol8CS1(inneraileron)attherearspar.AsubsequentinspectionoftheRHwingrevealedsimilarcracksonbothouterbrackets.Theaircraftinquestionhadaccumulated14,261flightcycles”.TheSBwasrestricted(byManufacturer’sserialnumber)toaircraftwhichhadcompletedmorethan10,000flightcycles(FC)andwasclassifiedas“Recommended”whichmeansthatitshouldbecarriedoutattheearliestopportunitysubjecttotheavailabilityoffacilitiesandqualifiedpersonnel.
TheOperator’sMaintenanceContractedServiceProvider(CSP)receivedtheSBinFebruary2009.TheCSPdeterminedthattheSBwasapplicabletothesubjectaircraftandanotheroftheoperator’saircraft.TheSBcalledforaHighFrequencyEddyCurrent(HFEC)inspectionofinnerandouterservo-controlattachmentbrackets,designated8CS1(lefthandwing)and8CS2(righthandwing).TheSBincludedapictureofthepairofbracketstobeinspected;however,thepictureincorrectlyshowedthebracketsfortheinactiveservocontrolratherthantheintendedactiveservocontrolbrackets.TheCSPraisedthenecessaryEngineeringOrderandrelatedinstructionsfortheaccomplishmentoftheSB.TheSBwasaccomplishedduringaC-CheckataMaintenance,RepairandOverhaul(MRO)facility,on22December2009.NoadversefindingswererecordedfollowingaccomplishmentoftheSB.
On9July2009,SBA330-57-3109wasrevised(Revision01,09July2009)followingthediscoveryofcrackingonthebracketsofanaircraftwhichhadaccumulated8,930flightcyclesi.e.lessthantheoriginalinspectionthresholdsetbytheManufacturer.Thenewthresholdwassetat7,500flightcycles.
12
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
1.17.2 HFEC Inspection
TheInvestigationinterviewedtheInspectorwhocarriedoutSBA330-57-3109attheMROfacility.TheInspectorheldcertificationissuedbytheBritishInstituteofNon-DestructiveTesting,whichwasvaliduntil6November2011.TheInvestigationwasalsoshownhisCompanyProceduresandHumanFactorstrainingcertification,whichwerealsovalidandindate.
TheInspectorinformedtheInvestigationthatonthedayoftheSBaccomplishment,itwashisonlyworktaskandthathehadnotbeensubjecttoanydistractions.UsinganotheraircraftattheMROfacility,theInspectordemonstratedhowhehadcarriedouttheInspection.Thedemonstrationshowedthatusingtheprescribedmethodofinspectionitwasdifficultforaninspectortopreventtheprobefromslippingofftheedgeofthebracketbeingsurveyed.Suchslippingcausedfalsereadings.DuringthedemonstrationtheInspectorshowedgoodunderstandingofthetechnique,andrepositionedtheprobeeachtimeitslippedtoensurethatthefinalresultoftheHFECinspectionwasvalid.
TheInvestigationreviewedthecalibrationhistoryforthetestequipment.Theunithadbeencalibratedon28January2009andwasnextduecalibrationon28January2010.Atthecalibrationon28January2010theunitwasfoundtobewithinthecalibrationtolerance.Inaddition,priortoeachuseoftheHFECequipmentAirbusNon-DestructiveTestingManualrequireslocalcalibrationusingsamplecalibrationblocks.Thesecalibrationblocksarelocallymanufacturedblockswithmachinedslotsrunningtoavarietyofdepths.TheInvestigationfoundthattherewasappropriatecertificationfortheseblocks.
DuringhisinterviewtheHFECInspectorrecalledthattheFINcodemarkingdecalwasmissingfromtheRHinboardaileronactiveservo-control.SubsequentinspectionofEI-ORDbytheOperatorconfirmedtheInspector’srecollection.TheOperatorarrangedforreplacementdecalstobefitted.
1.18 Meetings with the Aircraft Manufacturer
1.18.1 June 2010
On16June2010theInvestigationmetwiththeAircraftManufacturertodiscussthematter.TheManufacturerinformedtheInvestigationthatatthattimetherehadbeenatotalofseven(7)aileronactiveservobracketcrackingeventsrecorded.(Appendix A)Ofthese,tworesultedinfractureandseparation;thisincludedthesubjectevent.FouroftheeventsweredetectedasaresultoftheapplicationofSBA330-57-3109Version00.
Atthetimeofthemeetinglaboratorytestsonsixaffectedbracketshadrevealedsurfacepittingtodepthsof50microns;thispittingwasthesiteofthecrackinitiation.Fatiguestriationswereinevidenceinmostofthecracks;crackswithalengthuptoabout4mmexhibitedatypicalstriationspacingofapproximately2microns.
Therewaslittleevidenceofcorrosionwithinthepitsandthepresenceofprimerinthepitssuggeststhatthepittingwastheresincemanufacture.
TheManufacturerhadidentifiedadegreasingprocessknownas“pickling”usedinthemanufacturerofthebracketsasthelikelycauseofthesurfacepitting.PriortoMay2003thepicklingprocesswasamanualprocess,thereafteritwasautomated.TheManufacturerstatedthatabracketrandomlyselectedfromtheproductionlinein2008wasfoundtogenerallyhaveasurfacefinishbetterthantheproductiondrawingrequirementof2.4microns,thoughasmallnumberofisolatedpitsofupto20micronsdepthwereidentifiedandbelievedtobeduetomachining.During
13
manufacturingthebracketsarefullymachinedbeforethesurfacefinishischecked.Thebracketsarethendegreasedandcleanedpriortoanodisingandpost-anodisingthebracketsarepaintedandre-workedasnecessary.Withnosurfacefinishcheckafterthedegreasing(“pickling”)thevariabilityassociatedwiththemanualnatureoftheprocessmeantthatpitsofvaryingdepthcouldbepresent(undetected)inthefinishedbracket.
TheInvestigationraisedanumberofissueswiththeAircraftManufacturer,namely,
• ThelackofclarityinthetitleofSBA330-57-3109.“WINGS–INNERAILERONSREARSPAROUTERATTACHMENTS–INSPECTIONOFOUTERBRACKETS”couldmistakenlybeconstruedtomeanthatonlytheouterbracketsontheoutsideservo-controloftheinboardaileronrequiredinspection.
• ThediagramintheSBshowedthebracketpairfortheinsideservo-controlinsteadofthebracketpairfortheoutsideservo-control.(Figure No. 3)
• WhywastheSBone-offratherthanrepetitiveinnature? • WhydidtheSBnotprescribeacomplianceperiod? • Whyweresomeaircraftexcludedfromtheapplicabilitytable? • Wasthereariskofafuelleakduetotheassociateddeformationofthebottomskinofthe
wing? • NeedtoreviewtheaircrafthandlingimplicationsofEI-ORD’sbracketfailure. • NeedtoconductacrackagestudyonEI-ORD’sfailedbracketstoassessifitwaslikelythat
therewerecrackspresentwhenthebracketswereHFECinspectedinDecember2009.
Figure No. 3: Original SB Diagram showing incorrect bracket pair
14
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
1.18.1 October 2010
On27October2010theInvestigationmetwiththeAircraftManufactureragaintoreviewprogressonthemattersincethepreviousmeeting.
InrelationtotheSB,theAircraftManufactureradvisedthatitwasre-issued(Version02,08September2010)withanewtitle“WINGS-INNERAILERONSREARSPARATTACHMENTS-INSPECTIONOFOUTBOARDACTUATORBRACKETS”.ServiceBulletinA330-57-3109Version02increasedtherecommendednumberofoperatorsrequiredtoaccomplishtheinspectionfromonetotwo.ThereasonfortheSBwaschangedfrom“AnoperatorreportedcracksonbothbracketsattachingtheL/HActiveServoControl8CS1(inneraileronsattherearspar…”to“AnoperatorreportedaruptureofboththepairofattachmentbracketsfortheoutboardL/HServoControl*8CS1)oftheinneraileron...”ServiceBulletinA330-57-3109Version02alsopicturesthecorrectbracketpair(Figure No. 4),includesnotesonnon-destructivetesting,graphicsdepictingthetypicalcracklocationanddetailsforalocallymanufacturedplasticguidetoaddresstheproblemswiththeprobeslippingoffthebracketedge.OnthequestionofrepetitiveintervalstheManufacturersubsequentlyinformedtheInvestigationthatthefollowingintervalswerepublishedintheServiceBulletinA330-57-3109Revision03on31May2011:
• FortheA330,ISB57-3109R3setstherepetitiveintervalasThreshold=6000FC/19400FH3,Interval=1800FC/5700FH.
• FortheA340,ISB57-4119R3setstherepetitiveintervalasThreshold=3600FC/20600FH,Interval=1700FC/9600FH
Figure No. 4: Revised SB diagram showing correct bracket pair
3 FH:FlightHours
15
Onthequestionofpossiblefuelleak,theAircraftManufacturerstatedthatinbotheventsinvolvingbracketfracturetherewasnodeformationofthebottomskinundertherearsparnorwasthereanyholeelongationorrecordeddamagetothesparflangefasteners.TheManufacturerconcludedthattherewasthusnoriskoffuelleakfromthesparflangebolting(Primaryleakpath).InthecaseofEI-ORDtherewassomelocaliseddeformationofthetwolowerfastenersthroughtheaileronattachmentbracketandRearSparweblocations.However,theManufacturerconcludedthattherewasalowriskoffuelleakfromthesefastenersandthatinanycasetheriskwasmitigatedbythesealingandovercoatingofthefastenersduringinstallationandthelowmagnitudeoftheholedeformation.
AsaresultofthisanalysisbytheManufactureritwasconcludedthattheriskofasignificantfuelleakduetothefractureofanaileronbracketwasclassifiedasverylow.
TheAircraftManufactureralsoconsideredthepossibleimplicationsforaircrafthandlingofabracketfailure.TheManufacturerconductedanengineeringassessmentofthehandlingqualities/behaviouroftheaircraftwith1or2inboardaileronsatzerohingemomentposition,asaresultofrupturedactiveservocontrolbrackets.TheManufacturerconcludedthatthereisalwaysenoughlateralcontrol(usually,lessthan5degreesspoilerdeflectionwithover35degreesavailable)tocounterthefailure(s)withverysimilardynamics.TheManufactureradvisedthattheriskofflutterhadbeenreviewedandpresentedtoEASAatthe75thAirworthinessReviewMeeting(ARM)on22/23September2010).TheminutesoftheARMmeetingrecord:“Fluttercanonlybecausedbythecompleteseparationofbothactiveanddampingservocontrols.Thiscannotbecausedbythepresentissueasonlytheactiveservocontrolbracketsoftheinneraileronsisimpacted.Thereisnoriskofflutter”.TheManufacturerstatedthattheclassificationof“MINORimpactonAirworthiness”wasagreedbyEASA(atthe75thARM).
Onthequestionofcrackageestimation,theManufactureradvisedthatthegrowthofasmallflaw(defect)tothepointofrupturecouldnotbedeterminedexactly,butisestimatedtobeseveralthousandflightcycles.EI-ORDwasinspectedinaccordancewiththeSBat15,987FC(55,303FH).Thebracketfracturedat16,183FC(56,180FH).Thus196FC(877FH)hadelapsedbetweentheSBaccomplishmentandtheruptureofthebrackets.Examinationrevealedthatthefinalcrackhadgrownto48mmpriortobracketfracture.Striationspacingwasrelativelyuniformforthefirst10mmofgrowthat1micron.AlthoughitwasdifficulttorelateFCdirectlytoloadapplicationsManufacturer’sengineeringdataandanalysisindicatedthatanassumptionofonemajorfatiguestriationperflightcyclewouldberepresentative.Basedonthisassumptionthelaboratoryanalysissuggeststhatthecrackwouldhavebeenoftheorderof10mminlengthatthetimeoftheSBaccomplishment(HFECinspection).Inconclusion,theManufacturer’slaboratorytestingandanalysissuggestedthatitwashighlyprobablethatthecrackswerepresentduringtheoriginalSBinspectioninDecember2009.
1.19 Useful or Effective Investigation Techniques
Notapplicable.
16
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
2. ANALYSIS
Thiseventwascausedbythefailureoftheinboardaileronoutsideservo-controlouterbracket(F575-50989)ontheRHwingduetofatiguecracking.Theoutsideservo-controlinnerbracket(F575-50987)failedinoverloadasaconsequenceofthefailureoftheouterbracket.Thecorrespondingbracketpaironthelefthandwingwasinspectedandfoundtobecracked.ThetriggeringeventforthisfailurewasanaircraftencounterwithturbulenceoverIceland.
TheFlightCrewdetectedtheeffectsofthefailurealthoughtherewasnospecificindicationoftheeventontheECAM.TheFlightCrewfollowedastructuredapproachtotroubleshootingtheproblemandconsideredallpertinentfactorsbeforemakingthebalanceddecisiontocontinuetotheirdestination.
TheManufacturerhadissuedarecommendedSBrequiringinspectionoftheaffectedbracketsusingHFEC.TheOperator’sMaintenanceManagementSystemcorrectlyscheduledtheSBforaccomplishment.On22December2009,196FCpriortofailure,theSBwascarriedoutbyasuitablyqualifiedinspectorusingproperlycalibratedequipment,freefromanydistractions.TheInspectorwhocarriedouttheinspectionhadclearrecalloftheaircraftandevenrecalledamissingdecalwhichtheOperatorsubsequentlyconfirmed(andreplaced).However,theinspectiondidnotdetectanycracks.Followingtheevent,theManufacturerindicatedfromstudiesofthefeaturesofthefatiguecrackinthefailedbracketthatitwaslikelythatcrackswerepresentwhentheSBwascarriedout.ThereisnoclearexplanationastowhytheinitialapplicationoftheSBdidnotdetectthepresenceofcracks.However,theInvestigationdididentifythattheprocedureprescribedintheSBwaspronetoprobeslippagewhichcausedfalsepositivereadings.InadditiontheoriginalSBcontainedadiagramofthewrongbracketpairandcouldhavecausedconfusion,althoughthereisnoevidencethatsuchconfusionwasafactorinthisparticularapplicationoftheSB.TheManufacturerre-issuedtheSBwith,interalia,adiagramofthecorrectbracketpairanddetailsofalocallymanufacturedguidetoamelioratetheprobeslippageproblem.
Thefailedbracket’sfatiguecrackswerefoundtohaveoriginatedfroma50micronpitwhichwasprobablypresentsincemanufacture.Thepitwaslikelyduetoamanual“pickling”process,whichhasbeenautomatedsince2003.Testsonaproductionstockbracketindicatethattheautomatedprocedurehasaddressedthepittingproblem.
TheeventwasclassifiedbytheManufacturer(andacceptedbyEASA)ashavingaminorimpactonairworthinessandtheriskofanyassociatedfuelleakwasdeemedtobeverylow.
17
3. CONCLUSIONS
(a) Findings
1. TheaircraftencounteredturbulenceoverIcelandandduringautopilotcorrectionstoleveltheaircrafttheouterbracketattachingtheRHinboardaileron’sactive(outside)servotothewingrearsparfractured.
2. TheinnerbracketattachingtheRHinboardaileron’sactive(outside)servotothewingrearsparfailedasaresultoftheouterbracketfracturing.
3. Pittingofupto50micronsdepthwasfoundonthesurfaceofthefailedbracket. 4. Suchpittingprovidedthesitefortheinitiationoffatiguecracking. 5. Theproductiondrawingcalledforthebracketsurfacefinishleavingnopittinggreaterthan
2.4micronsindepth.Qualitycontrolchecksonproductionstockbracketsin2008foundthatgenerallythesurfacefinishwasbetterthantheproductiondrawingrequirementof2.4microns,thoughasmallnumberofisolatedpitsofupto20micronsdepthwereidentifiedandbelievedtobeduetomachining.
6. ThecauseofthepittingwastracedbytheManufacturertoamanualpicklingprocessusedpriortoMay2003,andwhichhadbeenautomatedsincethen.
7. InFebruary2009,theManufacturerpublishedarecommendedSBcallingforHFECinspectionoftheaffectedbracketstodetermineifcrackswerepresent.
8. ThisbulletinwasaccomplishedonEI-ORDinDecember2009andnocracksweredetected. 9. TheInspectorwhocarriedouttheHFECcheckwasproperlyqualifiedandtheequipment
usedwasproperlycalibrated. 10.DuringtheexaminationprescribedintheoriginalSBitwasfoundthetestingprobewas
pronetoslippingofftheedgeofthebracketcausingfalsereadings. 11.TheoriginalSBhadapotentiallymisleadingtitleandcontainedadiagramshowingthe
wrongsetofbrackets. 12.TheManufacturerre-issuedtheSBthreetimesreducingtheinspectionthresholdto
7,500flightcycles(Version01,9July2009),correctingthetitleandbracketdiagram,recommendingtwoInspectorscarryouttheworkanddetailingaplasticguidefortheHFECinspection(Version02,8September2010)andmandatingrepetitiveinspections(Version03,31May2011).
13.TheManufacturer’slaboratorytestingandanalysissuggestedthatitwashighlyprobablethatcrackswerepresentduringtheoriginalSBinspectioninDecember2009.
14. Intotal,acrosstheA330/A340fleet,therewerefivepartialcrackingeventsandtwofullruptureevents,thelastofwhich(partialcrack)wasin2010.
15.Atthe75thAirworthinessReviewMeetingbetweenEASAandtheManufacturertheeventwasclassifiedashaving“MINORimpactonAirworthiness”.
16.Theriskoffuelleakfollowingthefailureofthebracketswasclassifiedasverylow.
(b) Probable Cause
1. FractureoftheouterbracketattachingtheRHinboardaileron’sactive(outside)servo,duetofatigue.
(c) Contributory Cause(s)
1. Manual“pickling”processwhichcausedsurfacepittinggreaterthanthatallowedorprescribedintheManufacturer’sdrawings
2. FailuretodetectcracksduringHFECinspectionprescribedinaManufacturer’sSB.
18
Air Accident Investigation Unit Report 2012-015
Airbus A330-301 EI-ORD Over Iceland 11 May 2010
4. SAFETY RECOMMENDATIONS
AstheManufacturerhaschangedthebracketmanufacturingprocesssince2003andhasrevisedtheSBtotakeaccountofissuesidentifiedduringthisInvestigation,thisInvestigationdoesnotsustainanySafetyRecommendations.
APPENDIx A
Year Aircraft Bracket Finding LH/RH FC FH P/N2007 A330-300 Fullcrackonbothlugsof
theInboardAileronouterbracket(8cS1).StaticfailureonIBbracket
LH 14216 45346 F575-50989(OBbracket)F575-50987(IBbracket)
2007 A330-300 Partialcracksonbothbrackets;fatiguegrowthevident
RH 14853 48116 F575-50989(OBbracket)F575-50987(IBbracket)
2009 A340-300 Partialcrack LH 8930 71688 F575-50989(OBbracket)
2009 A340-200 Partialcrack RH 10198 71989 F575-50989(OBbracket)
2010 A330-300 Fullcrack(subjectaircraft) LH/RH 16183 56180 F575-50989(OBbracket)F575-50987(IBbracket)
2010 A330-300 Partialcracks LH/RH 17457 59106 F575-50989(OBbracket)F575-50987(IBbracket)
2010 A330-300 PartialcrackMultiplebrackets
LH&RH 16828 58853
- END -
Produced by the Air Accident Investigation Unit
AAIU Reports are available on the internet www.aaiu.ie
In accordance with Annex 13 to the International Civil Aviation Organisation Convention, Regulation (EU) No 996/2010, and Statutory Instrument No. 460 of 2009, Air Navigation (Notification
and Investigation of Accidents, Serious Incidents and Incidents) Regulation, 2009, the sole purpose of these investigations is to prevent aviation accidents and serious incidents. It is not the purpose of any such accident investigation and the associated
investigation report to apportion blame or liability.
A safety recommendation shall in no case create a presumption of blame or liability for an occurrence.
A.A.I.U., Department of Transport Tourism and Sport, 2nd Floor, Leeson Lane, Dublin 2, Ireland.Tel (24x7): +353 1 604 1293 or +353 1 241 1777 Fax: +353 1 604 1514 Email: [email protected] Web: www.aaiu.ie