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## H.O.NEUBER T& ASSOCIATES , INC . :;j:,iT?€NTOF ' ADVANCE D COMPOSIT E APPUCATION S ^' - ' ^^O^rfAT'O' ^ MATEfllALS , DESIG N fiSTI^UCTURALANALYSIS . ^ ^ ' - ' ^• ' '^' ' "•

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### 7 Augus t201 1 U.S . Departmen t o fTransportatio n Docke tOperations , M-30> Wes t Buildin g Groun d Floor , Roo m W12-14 0 120 0 Ne wJerse yAvenu e S E Washingtoh , D C 2095 0 Re : Docl<etlvio . FAA-20il-0639 , Directorat e Identifie r2011-CE-016-A D Thi s Submissio n i s on e par t o ftw o part s furnishe d b yth e Internationa l Comanch e Societ y(ICiS ) i n respons e t o th e NPRM . IC S ha s 5 Technica l Director s t o suppor t membershi p question s an d concern s abou t th e maintenanc e o fthej rairplanes . I n addition , ther e i s a Flee tAirworthines s Corhmlttee , o fwhic h ther e ar e tw o Co-chairmen . Th e undersigne d i s on e o fth e tw o co-chairmen . A t m ysuggestion , th e response t o th e NPR M woul d b e i n tw o parts . Part1 woul d b e Organize d byDav e Fitzgerald , th e othe rco-chairmen , usin g 4 o f th e Technica l Directors , focusin g o n practica l aspect s o fComanch e maintenanc e an d th e effect s o fth e propose d AD , an d Part2 focusin g o n th e mor e technica l aspects . Pleas e fin d Attachmen t At o thi s lette rfo rth e submitte d comments .

Han s D . Neuber t DER T605393-N I Fiee tAirworthines s Committe e Co-Chairma h

605 1 PRAP O STREET^ ANAHEI M HILLS , C A9260 7 RES : (714 ) 9a8'Z50 4 OPFICE : (714 ) 996-136 508/06/201 1 23:3 5 71499B136 5 H D NEUBER T PAG E 0 2

Attachmen tA 

### Comment s t o Docke tNo . FAA-2011-0639 rDirectorat e

Identifie r2011-CE-016-A D Commen t1 : IC S agree s wit h th e nee d fo ra on e tim e inspectio n o fth e stabilato rhorn , torqu e tube , bearing s an d mountin g hardware . Ther e i s a hig h probabilit ytha tth e AN17 5 bolt s holdin g th e hor n t o th e torqu e tub e wil l b e corroded . Commen t2 : Th e reaso n tha tth e torqu e tub e assembly/contro l hor n hav e no tbee n previousl yinspecte d fo rcrack s i s du e t o th e fac tther e i s n o prio r Pipe rrequiremen tt o d o s o (Re fl : Pipe rServic e Manual , 10t h Rev. , Par tNo . 753-516 , Chapte rIII , Tabl e III-I , Sectio n E) . Commen t3 : Th e NPR M reference s Pipe rServic e Bulleti n 118 9 an d quote s Piper' s recommende d inspectio n intervals . Th e preliminar ycop yo fS B 118 9 ha s a fil e dat e o f2 1 Ma y2009 , whil e th e fina l releas e cop yi s date d 2 9 Marc h 2010 . Th e tw o copie s ar e identical . IC S believe s th e preliminar y(an d fina l version ) cop ywa s writte n base d o n a magazin e articl e withou tsubstantiatin g data , fiel d servic e history , o r engineerin g evaluation . IC S recommend s tha tth e FA Aevaluat e Piper' s S B 118 9 a s advisor yonly , a t best . Commen t4 : Th e NPR M reference s th e stabilato rhor n generically . Th e correc tpar ti s numbe rP/ N 20397-00 , an d shoul d b e s o state d i n th e AD . Commen t5 : IC S ha s conducte d a n extensiv e owne rsurve yo fhor n inspection s (Ref . 3) . Earl ycopie s o fthos e result s wer e submitte d t o th e FA A fo rreview . W e ar e findin g tha tmor e an d mor e owner s ar e performin g th e complet e disassembl yan d inspectio n i n anticipatio n o fth e AD . Wit h ove r 80 0 inspectio n report s now , thos e owner s whic h hav e complete d a vali d inspectio n shoul d b e give n specifi ccredi twithi n th e wordin g o fth e A D s o a n unnecessar yre-inspectio n wil l no tb e required . Commen t6 : Stres s corrosio n o faluminu m alloy s i s a calenda rtime-stres s state-environmen tconditio n problem . Tota l time-in-servic e o rfligh t hour s flow n ar e no tvali d measure s o fwhe n crackin g wil l occu r(Ref . 5) . IC S recommend s tha txx xhour s TI S inspectio n Interval s b e stricke n fro m08/06/201 1 23:3 5 714998136 5 HD NEUBER T PAG E 0 3

wordin g withi n th e AD . Calenda rtim e i s th e onl yvali d inspectio n interva l period . Commen t7 ; I tha s bee n show n b ytest , measuremen tan d detaile d analysi s (Refs : 2 an d 4 ) tha tth e ke yparamete rcausin g SC C i s excessiv e bol ttorqu e holdin g th e hor n t o th e torqu e tube . Thes e bolt s ar e A N 175-33 A clos e toleranc e bolts . Th e applicatio n o fthes e bolt s I s i n bol tshear , no tbol t tension . Fro m Referenc e 1 , 5/1 6 bolt s i n shea rshoul d b e torque d betwee n 60/8 5 inch - pounds , no tth e tensio n valu e o f100/14 0 inch-pound s (plu s nu t friction) . IC S strongl ybelieve s thi s torqu e requiremen tchang e alon e wil l ceas e SC C hor n crackin g i n th e future . Commen t8 : Referenc e 6 provide s a survivabilit ychar t(Figur e 11) , whic h show s tha t100 % survivabilit yo fC-rin g shor ttransvers e tes tspecimen s whe n expose d t o a 3.5 % NaC I solutio n whe n tensio n stres s I s les s tha n 3 5 ks i stress . Th e alloy s plotte d ar e 7075-T6 5 an d 2219-T87 . IC S believe s tha t2014-T 6 wil l behav e similarly . Require d inspectio n interval s shoul d b e base d o n specime n surviva l rat e base d o n hor n stress . IC S ha s alread y demonstrate d tha tcritica l hor n stres s i s 1/5 o fth e critica l stres s show n i n th e Figur e 1 1 o fReferenc e 6 . IC S strongl yrecommend s tha tth e FA AInstruc tNIA R t o conduc tC-rin g testin g pe rReferenc e 6 t o determin e stres s stat e threshol d fo rSC C t o occur . IC S furthe rrecommend s tha tinspectio n interval s b e base d o n thes e tes t results , no tirrationa l TI S value s base d o n speculation . Commen t9 : Withi n th e wordin g o fth e AD , IC S recommend s tha ta terminatin g actio n b e stated . IC S ha s determine d tha ta numbe ro f 180/250/26 0 Comanche s cam e fro m th e factor ywit h thic k walle d tubes . Clearly , thes e ar e no tconformin g t o th e TC . Pipe rrefuse s t o acknowledg e thi s fact . Athic k

walle d torqu e tub e I s considere d terminatin g action . Pipe rrefuse s t o produc e thic k walle d torqu e tubes , statin g tha t i t doe s no t hav e th e resource s o rengineerin g tim e t o develo p thes e Items . The yclai m tha tflutte ran d fligh ttestin g woul d b e required . Installatio n o fthes e thic k torqu e tube s o n th e single s coul d no thav e bee n authorize d withou t engineerin g disposition , therefor e thei rinstallatio n ha s bee n Pipe rapproved . Wit h thes e fou rexamples , ove r14,00 0 troubl e fre e fligh thour s hav e show n tha tth e incorporatio n o fth e thic k walle d torqu e tube s i s a saf e conditio n an d meet s th e equivalen tsafet yo fth e 30/3 9 an d 24-40 0 models .08/06/201 1 23:3 5 714998136 5 HD NEUBER T PAG E 0 4



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### Commen t 10 : IC S recommend s tha t th e A D shoul d contai n a surve yfor m tha towners/inspector s submi t t o bot h th e FA Aan d IC S whe n a cracke d hor n o ra thic k

walle d torqu e tub e i s found .



### Reference s 1 . Pipe rServic e Manual , 10t h Revision , 1 Apri l 2009 , P/ N 753-516 . 2 . "Pipe rComanch e Hor n Cracking" , lette rdate d 1 7 Apri l 2011 , Eri cPau l & Denn yHaskin s t o Gregory(Keith ) Noles , Atlant a ACQ .0B/0B;201 1 23:3 5 714998136 5 HD NEUBER T PAG E 0 6



### 3 . "Cracke d Torqu e Tub e Hor n Surve yResults_Re vA" , PowerPoin t Presentation , Update d 2 0 No v2009 . 4 . "Comanch e Stabilato rHor n Crackin g Investigatio n - Fina l Analysi s Report" , PowerPoin t Presentation , 1 7 Ma y2011 . 5 . "Stress-Corrosio n an d Corrosion-Fatigu e Susceptibilit yo fHigh-Strengt h Aluminu m Alloys" , AFML-TR-70-259 , WPAFB , Ohio , Novembe r1970 . 6 . "Tim e Exposur e Studie s o n Stres s Corrosio n Crackin g o fAluminu m 2014 - T6 , 2219-T87 , 2014-T651 , 7075-T651 , an d Titaniu m 6AI-4V" , Fina l Report , 1 Jun e 1973 , Gramblin g College , Dept . o fPhysics , Grambling , Louisiana .