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maintenance and certificationSmoke in the Cabin—Landing Light Switch Failure ..................................................................................................... page 17Canada-U.S. Bilateral Aviation Safety Agreement ........................................................................................................ page 19

Smoke in the Cabin—Landing Light Switch FailureThe following occurrence resulted in two aviation safety advisories from the Transportation Safety Board of Canada (TSB).

BackgroundOnSeptember24,2007,aCessna152aircrafttookofffromtheOshawaMunicipalAirport,Ont.,withthepilotandpassengeronboard,destinedtoKingston,Ont.Justafterclearingthecontrolzone,thepilotandpassengernoticedanelectricalodourandobservedasmallfireandsmokeemanatingfromthebottomoftheleftdashpanelwheretheaircraftlightingswitcheswerelocated.Thepassenger,sittingintherightfrontseat,reachedforanddischargedthefireextinguisher.Thefirewasquicklyextinguished,buttheextinguishingagentcloudedthecockpit,reducingvisibility.Thecockpitwindowswereopenedandvisibilityimprovedconsiderably.TheaircraftreturnedtotheOshawaairportandlandedwithoutfurtherincident.Thepilotsufferedaminorburntohislegwhentheplasticinstrumentpanelmeltedanddrippedontohisjeans.TheTSBissuedFinalReport A07O0264onJanuary 14, 2009,regardingthisoccurrence.

Front of instrument panel

TheTSBdeterminedthatthelandinglightswitchinstalledintheoccurrenceaircraftwasbeyonditsdesigncapabilityandthereforewasunsuitableforthecircuititwascontrolling.Excessiveheatfromarcingandoxidizationwithintheswitchweakenedtheswitchstructureandcontactsupport,allowingthecontactstofalloutorbeexposed.Arcingfromthecontactscausedoilresiduetoflash,whichignitedanearbydustaccumulationandstartedthefire.Combustionwassustainedbytheplasticinstrumentpanel.TheTSBstatedthatsimilarlandinglightswitchsystemsareincorporatedonmost

oftheCessna 100-seriesaircraft,therebyincreasingthelikelihoodofasimilarevent.TheTSBissuedtwoaviationsafetyadvisoriesasaresultoftheirinvestigation.

Advisory No. 1: Landing light switch failureThelandinglightelectricalcircuitiscomposedofa15-amppush-to-resetcircuitbreakerinserieswithasinglepole,singlethrowrockerswitch,whichisinserieswitha28 VDC250-wattincandescentlamp.Theswitchandthecircuitbreakerarelocatedonthelowerinstrumentpaneltotherightofandabovethepilot’skneewhenseatedintheleft-handseat.Theengineoilpressureandtemperaturegaugesarelocateddirectlyabovethelandinglightswitch.Theoilpressuregaugeisconnectedtotheoil-carryingpressureline,whichisdirectlyconnectedtotheengine.Thistypeofcircuitandinstrumentpanellayoutarecommonamongstthe100-series Cessnaaircraft.

Theswitchwasidentifiedasarocker-styleswitchratedat10A250VAC,15A125VAC,3/4HP125-250VAC.NoDCratingswerefoundforthisswitch.Theswitchshowedevidenceofmeltdamagebeginningatthebaseandprogressingupwardonbothsides.Thesamedamagewasevidentontheinterioroftheswitch.Theswitchexteriorhadathickcoatingofdustandanoilyresidue,whichwasalsofoundinsidetheswitch.Ascanningelectronmicroscope (SEM)andenergydispersivespectroscopy (EDS)analysisoftheresidueindicatedthatitmighthavebeenengineoil.

Thelandinglightcircuitwiresremainedattachedtothecontactbutshowedevidenceoffiredamagenearwherethecontactenterstheswitch.Thecontactwascoatedwiththeplasticcasingmaterialandwhenthesurfacewasexaminedtherewasevidenceofrepeatedarcing,whichhadseverelyerodedthecontact’ssurface.Arcingwithinthelandinglightswitchcouldhaveprovidedtheignitionsourcenecessaryforafiretostart.Thedustcoveringevidentontheswitchandtheoilresidueprovidedbypossibleseepagefromtheoilpressuregaugelinelocatedabovetheswitchmayhaveprovidedthekindlingnecessarytostartafire.Theoilwouldconsistentlyreachitsflashpointwhenexposedtoarcing,andwhenitwasinproximitytothedustitwouldcausethedusttoignite.Asmallsectionoftheplasticinstrumentpanelwastestedforflammabilitybyintroducingadirectflametothe

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plastic.Thepieceofpanelreadilyignitedandsustainedflame.Italsoproducedgasesthatwerequiteharshwheninhaled,andwithoutsufficientventilationmaycausesomeincapacitationtothepilot.

AccordingtotheU.S.FederalAviationAdministration (FAA)AdvisoryCircular43.13-1B,chapter11(pages 11–17),becauseoftheinitialcurrentencounteredbyswitchescontrolling28 VDClamploads (incandescentlamps),theswitchesshouldhaveaderatingfactorof8.Thisaircraft’sswitchcontrolsa250-wattlampinacircuitpoweredby28 VDC,andshouldhaveaminimumDCcurrentratingof71 amps.TheswitchfromtheaircrafthadanACrating.TheAdvisory Circularhasawarningthatreads“Do not use AC derated switches in DC circuits. AC switches will not carry the same amperage as a DC switch.”Theswitchmanufacturerwascontactedandprovidedwiththelandinglightcircuitandswitchinformation.Afterevaluatingtheinformation,theyconfirmedthattheswitchwasnotdesignedtohandlethelamploads described.Thecircuitbreakerwasidentifiedasa15-amppush-to-resetcircuitbreaker (CB),CessnapartnumberS1360-15L.ThepurposeoftheCBinthecircuitistoprotectthe circuitwiring,notthecomponentsattachedtothewiring.The15-ampthermal-typeCBwasfoundtobesuitableforthecircuit.TheCBdidnottripaftertheoccurrencebut,beingthethermal-typeofCB,itdoesnotreactinstantaneouslytoanover-currentcondition.Thisfeatureisnecessarybecausewhenthelightswitchisselected“ON”,theinitialcurrentcanbeashighas15 timesitsratedload.IftheCBweretoreactinstantly

to theinitialcurrentitwouldtripeverytimetheswitchwasselected“ON”.

AsearchoftheFAA’sservicedifficultyreport (SDR)databasebytheTSBrevealed23 eventssimilartothisoccurrence.Thecommontermswere:smellorsmokeincockpit,landinglightswitchhot,landinglightswitcharcing,landinglightswitchmelted,andcircuitbreakerdid nottrip.

Duetothenumberoftheseaircraftpresentlyinuseworldwide,includinginflighttrainingschools,thepossibilitythatthistypeofeventmayrecuronaircraftthathavetheAC-ratedlandinglightswitchinstalledcannotbediscounted.Ifthistypeofeventweretooccurtoaninexperiencedpilot,ortoastudent-pilotonasoloflight,thepilot’sattentioncouldbedivertedfromflyingtheaircrafttofocusonextinguishingthefire,withpossibledireconsequences.

TheTSBsuggestedthatTransport Canada (TC),inco-ordinationwiththeFAAandtheaircraftmanufacturer,maywishtotakeactiontomitigateoreliminatethethreatoffirecausedbyAC-ratedswitchesinthelandinglightDCcircuitofCessna152 aircraft.

Advisory No. 2: Smoke-in-cabin emergency proceduresThepilotandpassengerfollowedtheemergencyproceduresforanelectricalfireinthecabin,asperthepilot’soperatinghandbook (POH).Theprocedureswereperformedfrommemoryonly.Actingontheirowninstincts,theydecidedtoopenthetwocabinwindowstoquicklyimprovevisibilityandimproveairqualityintheconfinedareaofthecockpit.Theirquickactionsweresuccessfulandthepilotwasabletore-channelhisfullattentiontosafelyflyingtheaircraftbacktotheairport.

Reportedcasesofsmokeinthecockpitaboundinvarioustypesofgeneralaviation (GA)aircraftworldwide.Apilot’sabilitytoflytheaircraftsafelyisdegradedbythepresenceofsmokeandextinguishingagentsinthecockpit.Takingactiontoremovethesmokeandfumesfromextinguishingagentswouldincreasevisibilityandimprovetheairqualitywithintheaircraft.

Toensurethatpilotscanquicklyeliminatesmokeandextinguishingagentfumesfromthecockpit,furtherchecklistorproceduralitemsmayberequired.TheTSBthereforesuggestedthatTC,inconcertwithmanufacturersandtheregulatoryauthoritiesofothercountries,maywishtoreviewemergencychecklistproceduresdealingwithsmokeandfireonGAaircraftandtoincludeanadditionalsteptoeliminatesmokeor fumes.

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Rear of instrument panel

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Safety action takenTCcontactedtheFAA,theauthorityforthestateofdesign,requestingtheirpositionandpossiblecorrectiveaction.TheFAAapproachedCessnawhodevelopedacorrectiveactionplan.

Landing light switchTheFAAtookactiontomitigateoreliminatethethreatoffirecausedbyAC-ratedswitchesinthelandinglightDCcircuitofCessna 152aircraft.Cessnaco-operatedwiththeFAAbyissuingMandatoryServiceBulletinsMEB09-3andSEB09-6datedMay 11, 2009,toremoveandreplaceallsubjectswitchesusedinthelandinglightaswellasthetaxilightandrotatingbeaconcircuitsinthe100-,200-and300-seriesCessnamodelswithservicelifegreaterthanfouryears.ThisincludestheCessna 152-seriesaircraft.Thesebulletinsaretobeaccomplishedwithinthenext400 hoursofoperation,or12 calendarmonths,whichevercomesfirst.Areviewofthedatabaseshowslessthan1percentofthefleethasbeenaffectedbythistypeoffailure.Therefore,theFAA’scourseofactionhasbeentodisseminatetheconcernbyissuingaSpecialAirworthinessInformationBulletin (SAIB)CE-09-42,whichisavailableatwww.faa.gov/aircraft/safety/alerts/SAIB/.

Smoke-in-cabin emergency proceduresTheFAAtookactionbyreviewingtheemergencychecklistproceduresdealingwithsmokeandfirein

GAaircraftandincludingadditionalstepstoeliminatesmokeorfumes.TheFAA’scourseofactionhasbeentodisseminatethisinformationbyissuingSAIBCE-10-04,whichisavailableatwww.faa.gov/aircraft/safety/alerts/SAIB/.ItrecommendsthatownersandoperatorschecktheirPOHoraircraftflightmanual (AFM)andaddastatement:“toremovesmokeandfumesfromthecockpit,dothefollowing…”IfsuchastatementdoesnotexistintheirPOHorAFM,ownersandoperatorsareencouragedtocontacttheaircraftmanufacturerforchecklistinstructionsfortheremovalofsmokeorfumesfromthecockpit (e.g.closingoropeningheating,air-conditioning,orairvents).

ConsideringtheFAA’sissuanceofthecorrespondingSAIBandthatCessnahasforwardedtheapplicableserviceinformationtoallsubscribersofsuchpublications,TChasnottakenanyadditionalactionatthistime.

In closing, TC would like to remind the community that defects, malfunctions and failures occurring on aeronautical products should be reported to Transport Canada, Continuing Airworthiness in accordance with CanadianAviationRegulation (CAR) 521 mandatory SDR requirements. These reports will serve as supporting documentation to present to the authority for the state of design or the manufacturer when corrective action is necessary.  

Canada-U.S. Bilateral Aviation Safety Agreementby Joel Virtanen, Civil Aviation Safety Inspector, Maintenance and Manufacturing, Standards, Civil Aviation, Transport Canada

IthasrecentlycometoTransportCanadaCivilAviation’s (TCCA)attentionthatmoreawarenessisrequiredontheimpactofinternationalagreementsontheCanadianaviationindustry.ThisarticlewillhelpaddressthisconcernbyfocusingontheCanada-U.S.BilateralAviationSafetyAgreement (BASA),itsassociatedmaintenanceimplementationprocedures (MIP),andhowtheyapplytoaviationprofessionalsinCanada.

OnJune 12, 2000,CanadaandtheUnited StatessignedtheBASAanddesignatedtheirrespectivecivilaviationauthoritiesastheexecutiveagentsforitsimplementation.TheAgreementcanbeviewedat:www.tc.gc.ca/eng/civilaviation/standards/int-baa-usa-2000-3676.htm.

TheBASAprovidesfor,amongotherthings,thereciprocalacceptanceofairworthinessapprovalsandenvironmentaltestingandapprovalofcivilaeronauticalproducts,aswellasapprovalsandmonitoringofmaintenance,alterationand/ormodificationfacilities,maintenancetrainingorganizations,andmaintenance personnel.

ArticleIII (B)oftheBASArequiredthattheU.S.FederalAviationAdministration (FAA)andTCCA—beingtheexecutiveagentsfortheParties—draftwrittenmethodsbywhichsuchreciprocalacceptanceswouldbemade.ThisdocumentedprocessisreferredtoastheImplementationProceduresgenerally,andthedetailedprocedureforthereciprocalacceptanceofmaintenanceactivitiesandpersonnelisdescribedintheMIP.TheMIPcanbeviewedat:www.tc.gc.ca/eng/civilaviation/standards/int-ta-usaimp2006-menu-3700.htm.

TheobjectiveoftheMIPistooutlinethetermsandconditionsunderwhichtheFAAandTCCAcanaccepteachother’sinspectionsandevaluations,includingFAA-approvedFederal Aviation Regulations (FARs)Part 145repairstationsandCanadianapprovedmaintenanceorganizations (AMO).TheMIPalsoappliestoFAA-certificatedairmenandCanadianaircraftmaintenanceengineers (AME).Asaresult,thefindingsofcomplianceandregulatoryoversightbyeitheragencywillbeacceptedbytheotheragency.Thiswillleadtoareductioninredundantinspectionswithoutadverselyaffectingaviation safety.

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