ExemptionNo.11075UNITEDSTATESOFAMERICADEPARTMENTOFTRANSPORTATIONFEDERALAVIATIONADMINISTRATIONBURLINGTON,MA01803-5229InthematterofthepetitionofROLLS-ROYCEpicforanexemptionfrom§33.27(f)(6)ofTitle14,CodeofFederalRegulationsRegulatoryDocketNo.FAA-2014-0609GRANTOFEXEMPTIONAugust13,2014,Rolls-Roycepic,ML-52,POBox31,Derby,DE248BJ,England,petitionedtheFederalAviationAdministration(FAA)foranexemptionfromTitle14,CodeofFederalRegulations(14CFR)§33.27(f)(6),Amendment33-31.Thepetitionerrequestsrelieffromthefollowingregulation:Section33.27(f)(6),Amendment33-31,Turbine,compressor,fan,andturbosuperchargerrotoroverspeed."(f)Failureofashaftsectionmaybeexcludedfromconsiderationindeterminingthehighestoverspeedthatwouldresultfromacompletelossofloadonaturbinerotoriftheapplicant:(6)Doesnotexcludetheentireshaft."PetitionerRolls-RoycerequeststheFAAgranttheexemptionbasedontwopoints.Petitioner'sfirstpointisthatforeachoftheTrentXWBenginemodelsitidentifies,thepetitionerhasshownthatthehigh-pressure(HP)turbinerotorburstspeedisgreaterthanI00%rotorterminalspeedresultingfromHPshaftsystemfailure.Petitioner'ssecondpointisthatcompliancewith§33.27cannotbeshown,absentanexemptionfrom§33.27(f)(6).Thepetitioneradds,however,thatcompliancecanbeshownwithoutadverselyaffectingsafety,iftheexemptionisgranted..Petitionerrequestsexemptionfrom14C.F.R.§33.27(f)(6)fortheHPshaftsystemofthefollowingTrentXWBenginemodels:ANE-14-425-EModelTrentXWB-84TrentXWB-79BTrentXWB-79TrentXWB-75Ratingx1000lbs.84797975Petitionerassertsthatasdemonstratedinitssubstantiatingreport,thelevelofsafetyaffordedbycompliancewith§33.27fortheHPshaftsystemwillbeunaffectedbythegrantingofanexemptionfrom§33.27(±)(6).Petitioneralsostatesthatgrantingthisexemptionwillpromoteandservethepublicinterest,andpetitioneridentifiedthosebenefitsinitspackage.Finally,petitioneralsoassertsthatgrantingitsexemptionwillhavenoadverseeffectonsafetyandprovidedthefollowinginsupportofthatcontention.1.TheHPshaftsystemdesignutilizedacrosstheTrentenginefamilydifferssignificantlyfromconventionalshaftsystems.AFailureModeandEffectAnalysisdeterminedthatnoknownorpotentialenvironmentalthreatstotheintegrityoftheHPshaftsystemcomponentsexistthatcouldleadtoalossofloadfailure.2.Thespecialcontrolsappliedtothetorque-transmittingcomponents(i.e.,theHPcompressorreardrumandtheHPturbinediscoftheHPshaftsystem)areofahigherstandardthanthoseofmanyothershaftsystemsinthepast.3.Theserviceexperienceofpetitioner'sthree-shaftfamilyofenginessupportsthetheoreticalassessmentofpoints1)and2)above,andallincorporatethesamedesignstylefortheHPshaftsystemastheenginemodelsthatarethesubjectofthispetition.Operationally,overmorethan250millionserviceflighthourshavebeenrecordedwithoutfailureofanyreportedHPshaftsystemtorquepathfailuresontheTrentfamilyofengines.Thisperformancetranslatestoafailurerateoflessthan2.8x10-9failuresperflighthour.FederalRegisterPublicationTheFAAdeterminedthatpublishingthepetitioner'srequestforexemptionintheFederalRegisterforpubliccommentwasnecessary,per14CFR11.87.AsummaryofthepetitionwaspublishedintheFederalRegisteronSeptember2,2014(79FR52104),fora10dayperiod.TheFAAreceivednocomments.ThecompletepetitionisavailableattheDepartmentofTransportation'sFederalDocketManagementSystemathttp://regulations.govunderDocketNo.FAA-2014-0609.2TheFAA'sAnalysisOurreviewofthepetitioner'spetitionandsupportingdataindicatesthatwhatthepetitionerseeksisnotanexemptionto§33.27(f)(6),butto§33.27(b)(3).Section§33.27(b)(3)requiresarotorburstmarginbegreaterthan5%ofrotorterminalspeed.Section33.27(f)(6)prohibitsexclusionoftheentireshaftsystemfromfailureconsideration.Petitionerrequestedthattheexemptionfrom§33.27(f)(6)begrantedonthebasisofitsdemonstrationthatforeachofthelistedenginemodels,theHPturbinerotorburstspeedisgreaterthan100%rotorterminalspeedresultingfromanHPshaftsystemfailure.Basedonwhatthepetitionerrequestedandwhatthepetitionerdemonstratedinitssupportingpackage,anexemptionto§33.27(f)(6)isnotapplicable.Rather,thepetitioner'srequestisapetitionforexemptionto§33.27(b)(3),andtherequirementthatrotorburstmarginbegreaterthan5%ofrotorterminalspeed.Therefore,weinterpretpetitioner'srequestasarequestforexemptionto§33.27(b)(3).WereviewedthedataprovidedbypetitionerandfindthattheHPturbinerotorburstspeedsfortheTrentXWBenginemodelsaregreaterthan100%rotorterminalspeedresultingfromanHPshaftsystemfailure.Basedonourfindingandthecompensatingfactorsthatthepetitionerdemonstratedthroughgoodserviceexperienceofsimilarthree-shaftdesignsystemsandevaluationofallknownfailuremodes,weconcludethatanexemptionto§33.27(b)(3)fortheTrentXWB-84,-79B,-79,and-75enginemodelswillhavenoadverseeffectonsafety.TheFAA'sDecisionInconsiderationoftheforegoing,andbasedontheFAA'sinterpretationofpetitionerRollsRoyce'sexemptionrequest,Ifindthatagrantofexemptionwillnotadverselyaffectthelevelofsafetyprovidedbytheregulationsandisinthepublicinterest.Therefore,pursuanttotheauthoritycontainedin49 U.S.C.§§106(f),40113and44701,delegatedtomebytheAdministrator,thepetitioner,Rolls-Royceplc,isherebygrantedanexemptionto§33.27(b)(3)forHPshaftsystemfailurewiththeconditionthattheHPturbinerotorburstspeedbegreaterthan100%rotorterminalspeedresultingfromHPshaftsystemfailure.IssuedinBurlington,Massachusetts,onOctober3,2014.fLc.·?Vlttw--jD'AlessandroAssistantManager,EngineandPropellerDirectorateAircraftCertificationService3