Reliability-Centered Maintenance (RCM)

1 EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Reliability-Centered Maintenance (RCM)The science of achievingbettersafety & dispatch reliabilityby doing lessmaintenance!EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Who uses RCM?Airlines(1970s-)zAir Transport Ass n MSG-3 Military aviation(1980s-)Non-aviation (industrial)Nuclear power plantsOil refineriesWater treatment plantsMarine vesselsHeavy equipment manufacturingEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Benefits of using RCM050100150200250300350 Components subject to scheduled overhaulor replacementDC-8: 339DC-10: 7 DCDC--8:8:TraditionalTraditionalDCDC--10 :10:RCMRCMEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Benefits of using RCM0500000100000015000002000000250000030 0000035000004000000 Man-hours of structural inspections(first 20,000 hours TIS)DC-8: 4,000,000B-747: 66,000 DCDC--8:8.

2 TraditionalTraditionalBB--747:747:RCMRCM EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Benefits of using RCMzRCM has saved the airlines a fortune byzSlashing the amount of scheduled PMzEliminating most TBOszBig surprise:When PM was slashed and TBOs eliminated, aircraft safety and dispatch reliability improved dramatically!zzQ:Q:How can doing LESS Maintenance result in MORE safety and reliability ?zzA:A:By reducing MIFs ( Maintenance -induced failures)EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393zMaintenance is inherently invasive it often breaks things that were previously working finezWe call this a Maintenance -induced failure (MIF)zThe more invasive the task, the more likely a MIFzPerforming unnecessary maintenancezWastes money and increases the risk of MIFzEliminating unnecessary maintenancezSaves money and improves safety and reliabilityMaintenance has a dark side!

3 Maintenance has a dark side! Maintenance has a dark side!EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Traditional vs. RCMzTraditional view:zMaintenance is a good thingzThe more we do, the betterzRCM view:zMaintenance is a necessary surgeryzThe less we do, the betterzWe should do it only when absolutely necessary, or when the benefits clearly outweigh the associated risks and costsEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Key RCM questionszWhat are this component s failure modes?zFor each failure mode:zHow likelyis this failure to occur?zIs the probability of this failure:zHigher when component is old? ( age-related )zHigher when component is young?

4 ( infant mortality )zUnrelated to component age? ( random )zHow serious are the consequencesof this failure?zCan we detectan incipient failure before it occurs?EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 TDM versus CDMzTime-directed Maintenance (TDM)zAttempts to avoid failures by retiring, replacing or overhauling components at a specific age (TBO)zCondition-directed Maintenance (CDM)zAttempts to avoid failures by monitoring component condition to detect potential failures before they become functional failureszCDM is always more efficient than TDMzTDM should be used only when CDM is infeasibleEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Hierarchy of consequenceszSafety consequenceszFailure might hurt or kill someonezExample.

5 Engine connecting rod failurezHidden consequenceszFailure invisible to crew, and might reduce safetyzExample:failure of standby vacuum systemzOperational consequenceszFailure might make aircraft unflyable (AOG)zExample:failure of a magnetozEconomic consequenceszFailure has no significant operational impactzExample:failure of #2 comm radioEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 RCM decision treeRisks damage?Impacts mission?Impacts safety?Is CDM effective?Is TDM effective?Perform CDMP erform TDMA ccept failure,redesign system,or add redundancyRun tofailureYesNoYesYesYesYesNoNoNoNoEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Age-related failuresTraditional few premature failuresUnacceptable rate of failureTBOTBOSafe LifeSafe LifeDo our piston Do our piston aircraft engines aircraft engines exhibit this exhibit this failure pattern?

6 Failure pattern?EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Engine-failure accidents(2001-2005 small piston airplanes)Age-related failuresEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Engine-failure accidents(2001-2005 small piston airplanes)????!!!!Past TBO?Past TBO?InfantInfant--mortality!mortality!Ag e-related failuresEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Age-related failuresSecond-generation AT TBO???OVERHAUL AT TBO??? Bathtub curveBathtub curve EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Age-related failuresThird-generation view (RCM).

7 Age-relatedNon-age-related77% to 92%8% to 23%TBO makes sense forTBO makes sense foronly 4% to 6% of theonly 4% to 6% of thecomponents on civil A/Ccomponents on civil A/CEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393zSimple itemszOne dominant failure mode ( , metal fatigue)zFailure probability often increases with agezAn age limit, safe-life limit, or TBO may be usefulzComplex itemszMany different failure modeszFailure probability usually doesn t increase with agezAge limits, safe-life limits and TBOs are not effectiveSimple vs. complexEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Condition monitoringRule of thumb:For condition monitoring to detect potential failures reliablyand prevent functional failures, we must inspect for potential failures at approximately one-half of the P-F inspection for potential failures (P) intended to prevent functional failures (F)EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Nowlan & Heap report: reliability centered Maintenance Dec.

8 1978, 520 Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Let s talk about an apparently healthy engine at TBO makes very little sensezComplex item, no single dominant failure modezso overhauling at TBO is not an effective method of reducing failure risk zMost likely catastrophic failure is infant mortalityzso overhauling arbitrarily at TBO is more likely to increase risk than decrease itzWhy throw away years of useful life?EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Let s talk about an engine beyond absolutely t void your aircraft t make the overhaul more t make a catastrophic failure more likelyzIn fact, it will do exactly the opposite!

9 EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393A tale of two engineszMy 1979 Cessna T310R has two TSIO-520-BBszTCM s published TBO is 1,400 hourszOn first run, these engines ran trouble-free for 1,900 hours SNEW, then field overhauledzWhy? Because I chickened out!(Pretty dumb, huh?)zAt teardown, engines immaculatezAll 12 cylinders re-valved and continued in servicezAt TBO (1,400 SMOH), running greatzAt 2,300+ SMOH (164% of TBO), still running finezThis time, I m in no hurry to overhaul!EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 TBO do s and don tszHow we shoulduse TBOzUse it to plan reserve for overhaulzUse it to adjust fair market valuezHow we should notuse TBOzDon t euthanize an engine just because it has attained some arbitrary agezWhy throw away years of useful life?

10 ZMonitor engine health using all available tools, and overhaul strictly on condition EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Compression testEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Compression testzMandated by FARs but problematic:zVery unrealistic test conditionszPoor precision and reproducibilityzSensitive to equipment, techniquezNumerous false positives tens of thousands of cylinders have been removed unnecessarily due to weak compression zNeverpull a jug solely because of a low compression reading!EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Compression testEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Oil filter inspectionEAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Oil filter inspectionzMandated by FARszVery important test, but has limitations:zWon t detect microscopic wear metal particles <20 micronszMay not detect large chunks >1/16 EAA Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Oil filter inspectionBut may notdetect detect Chapter 393 (June 2008)Copyright 2008 Savvy Aviator, 393 Oil filter never saw this!