Cylinder Safety ProgramJimmy Tubbs© AEC | 2Cylinder Safety Project•Statistics:–27,000 each 520/550 cylinders produced fromnov 2002 thru June 2008–24 confirmed head-to-barrel head thread fatiguefailures–7 failures on cylinders produced after 2005–Additional similar type failures (in FAA list)resulted from two additional failure modes•Head separation at top of barrel•Head & barrel disengaging© AEC | 3Cylinder Safety ProgramTime Line   © AEC | 4Cylinder Safety Project-Design History•AEC Replacement Cylinders:–Designed from continental cylinders–FAA knew of high continental cylinder head-tobarrel separation history•Was discussed in AEC certification documents•The Service Difficulty Reports from that timeshow more than 1200 Continental head-tobarrel separations between 1974 and 2012© AEC | 5Cylinder Safety ProgramAEC and OEM Head-BarrelSeparations 1974 To Today© AEC | 6Cylinder Safety Project-Search For Cause•FAA/NTSB Meeting In San Antonio In 2006–Wide Ranging Issues Discussed–Most Pressing Issue Was HB Separations–Suggestion To Develop Lab Testing Technique ToIdentify Root Cause For HB Separations© AEC | 7Cylinder Safety Project-Search For Cause•Lab testing in 2006-2007 time frame–Higher interferencefits were the result•Tests on Lycomingcylinders veryconclusive•Continental tests-notso much–Engine TestingNeeded© AEC | 8Cylinder Safety Project-Search For Cause•AEC Proposed Root Cause Engine Testing ToFAA In Late 2010 and Again in Early 2011•AEC Developed A Test Program Plan–Briefed FAA on Plan June 2011•Instrumentation, Engine Build and TestingStarted December 2011•Report 1202-2 Dated Feb. 20, 2012© AEC | 9Conductedinstrumentedengine testsin late 2011and early2012© AEC | 10Cylinder Safety Program•Cylinders instrumented at critical location with high temp strain gauges andthermocouples© AEC | 11Cylinder Safety Program•A range of interference fits were testedEngineCylinderPositionSealBandInterferenceThreadInterference#10.0080.012#20.010.012#30.0120.012#40.0140.012#50.0160.012#5Glazed0.0170.016#60.0180.012© AEC | 12Cylinder Safety ProgramTest Results:The test dataplotted as afunction of CHTExhaust Side Strain Trend Plots vs CHTPhase 2 Tests, TO Power200220240260280300320340360380400420440460480500520540300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620CHT, Deg. F

Strain, MicroinchesCyl #5Cyl #2Cyl #4© AEC | 13Cylinder Safety ProgramEffect ofBad Break-In© AEC | 14Results of NTSB Meeting Nov. 2012•Suggested FEA Correlated to Engine TestData•AEC Agreed On The Need–Delta G•Used AEC 3-D Model•Set Range of Boundary Conditions To SpanAssembly and Operation© AEC | 15ComputerModel© AEC | 16Stress with noseal bandfrictionShows seal bandcontributionessential© AEC | 17Stress with no sealband slipThread stress withinMaterial limitswith seal bandcontribution© AEC | 18Cylinder Safety Program•Analysis Supports AEC Position:–AEC631397 safe when operated within limits•With a margin–AEC Inspection and Removal at TBO•Pre-April 2006•All manufactured with less than .011 inchinterference•Give inspection credit for engine monitoringsystem© AEC | 19Cylinder Safety Program•What does the testing and analysis tell us?–Stresses become critical if:•CHT above published limits•Break-In attempt does not seal piston ringsand cylinder bore–New assembly practices will not prevent futurefailures, but does increase margins© AEC | 20Cylinder Safety Program•Effects of Higher Interference Fits–Higher interference fits will not prevent all futurehead-barrel separations•However, other failure modes caused byexcessive heat may cause failure before headbarrel separation–Most of the failure modes morecatastrophic than head-barrel separation© AEC | 21Cylinder Safety ProgramIndications ofOver Heat© AEC | 22•GOOD© AEC | 23Cylinder Safety Program•Causes of cylinder overheating–Induction leaks–Mixture–Malfunctioning or blocked injectors•Air side of turbocharged engines–Ignition timing–Spark Plugs•Loose•Broken insulators•Bad resistors© AEC | 24Cylinder Safety Program•What other factors are relevant?–CHT gauges not required for many airplanes–On many with CHT, only one cylinder monitored–CHT gauges not required to be calibrated–Mechanics not trained adequately about pistonengine Break-In procedures© AEC | 25Cylinder Safety Program•Factors (Cont)–In the old days-•Chrome bores were very difficult to Break-In•Oil burners were considered a nuisance, not asafety issue–Hundreds of head-barrel separations inpast years show that it was just acceptedas a part of aviation–We now know the root cause for head-barrelseparation, but changing is difficult!© AEC | 26Cylinder Safety Program•Discussions have been held with the SmallAirplane Directorate and GAMA–They believe that mandating old airplanes to beretrofitted with CHT gauges on all cylinders notpractical–Also, they believe it would be difficult to imposecalibration requirements on older airplanes–May be a way to address for new airplanes•ASTM F44© AEC | 27Cylinder Safety Program–Specifics•AEC suggests the following (as incorporatedin MSB 13-3):1. Recommend a repetitive inspection andremoval at overhaul of cylinders producedsince end of MSB 06-2 to April 20061. AEC does not have assembly data onthese cylinders, so cannot segregate intosubsets© AEC | 28Cylinder Safety ProgramSpecifics (Cont)2. Recommend a repetitive inspection andremoval at overhaul of cylinders producedsince 2006 with less than .011 seal bandinterference.1. The testing shows that this would provideadequate safety margin for temperatureexcursions2. Give Credit For Engine Monitors1. 50 Hr vs. Annual Inspection© AEC | 29Cylinder Safety Program•AEC Should:–Provide owners/operators with detailedinformation on the issue of high cylindertemperatures and glazed cylinder bores»SIB 12-2–Encourage Engine Monitoring© AEC | 30Cylinder Safety Program•FAA Advisory Data such as SAIB could beuseful•NTSB Advisory?•Root cause information should be shared–AEC working on publications–Mike Bush just published an article andanother to follow© AEC | 31Cylinder Safety Program•The NTSB:–Can promote a technical root cause basedapproach to this safety issue–Can encourage root cause issues to be providedto the aviation public by the FAAQuestions?