MIKE BUSCH HANDS ON / SAVVY AVIATOR

Critical Component Failures Reliability-Centered Maintenance, Part 3

TO PROPERLY APPLY RELIABILITY-CENTERED maintenance (RCM) prin- operating an engine after a prop strike. Both ciples to the maintenance of our aircraft engines, we need to TCM and Lycoming state that any incident analyze the failure modes and failure consequences of each major that damages the enough that it component part of those engines. has to be removed for repair warrants an Last month, we looked at the issue of catastrophic failures of pis- engine teardown inspection. This applies ton aircraft engines and saw that the predominant risk of such even to prop damage that occurs when the failures is greatest when the engine is young, not when it’s old. This engine isn’t running. Insurance will pay for month, we’ll examine the critical components of these engines, how the teardown and any necessary repairs, no they fail, what consequences those failures have on engine operation questions asked, so it’s a no-brainer. and safety of fl ight, and what sort of maintenance actions we can That leaves us with failures due to take to deal with those failures eff ectively and cost-effi ciently. oil starvation and/or bearing failure. We’ll talk about these when we look at oil pumps and bearings. It’s hard to think of a more serious piston engine failure mode than a crankshaft failure. If it fails, the engine quits. CRANKCASE Yet are rarely replaced at overhaul. Lycoming says its Crankcases are also rarely replaced at major crankshafts often remain in service for more than 14,000 hours and overhaul, and they often provide reliable 50 years. Teledyne Continental Motors (TCM) hasn’t published this service for many TBOs. If the case stays in sort of data, but TCM crankshafts probably have similar longevity. service long enough, it will eventually crack. Crankshafts fail in three ways: 1) infant-mortality failures due to The good news is that case cracks propagate improper material or manufacture; 2) failures following unreported slowly, so a detailed annual visual inspection prop strikes; and 3) failures secondary to oil starvation and/or bear- is suffi cient to detect such cracks before they ing failure. pose a threat to safety. Engine failures We’ve seen a rash of infant-mortality crankshaft failures in recent caused by case cracks are extremely rare. years. Both TCM and Lycoming have had major recalls of crankshafts that were either forged from bad steel or were physically damaged AND LIFTERS during manufacture. Those failures invariably occurred within the The cam/lifter interface endures more pres- fi rst 200 hours after a newly manufactured crankshaft entered ser- sure and friction than any other moving vice. If a crankshaft survives the fi rst 200 hours, we can be confi dent parts in the engine. The cam lobes and lifter that it was manufactured correctly and should perform reliably for faces must be hard and smooth in order to multiple TBOs. function and survive. Even tiny corrosion Unreported prop strikes seem to be getting rare because owners pits (caused by disuse or acid buildup in the and mechanics are becoming smarter about the high risk of oil) can lead to rapid destruction (spalling)

96 Sport Aviation March 2010 PHOTOGRAPHY BY BRADY LANE of the cam and lifters and dictate the need for a pre- mature teardown. This is the number one reason that engines fail to make TBO. This problem mainly aff ects owner-fl own airplanes because they tend to fl y irregularly and sit unfl own for weeks at a time. Camshaft and lifter problems seldom cause cata- strophic engine failures. The engine will continue to make power even with severely spalled cam lobes that have lost a lot of metal, although there is some small loss of power. Typically, the problem is discov- ered when the oil fi lter is cut open and found to be full of metal. If the oil fi lter isn’t cut open and inspected on a regular basis, the cam and lifter failure may progress undetected to the point that ferrous metal circulates through the oil system and contaminates the engine’s bearings. In rare cases, this can cause catastrophic engine failure. A program of regular oil-fi lter inspec- tion and oil analysis will prevent such failures. If the engine is fl own regularly, the cam and lifters can remain in pristine condition for thousands of hours. Some overhaul shops routinely replace the cam and lifters with new ones at major overhaul, but other shops use reground cams and lifters. Most knowl- edgeable engine experts agree that properly reground cams and lifters are just as reliable as new ones. FLIGHT GUIDE HAS THE SOLUTION FOR THE ACTIVE PILOT! GEARS The engine has lots of gears: crankshaft and camshaft FLIGHT GUIDE GOES IFR gears, oil pump and fuel pump drive gears, magneto ® and accessory drive gears, prop governor drive FLIGHT GUIDE eBOOK gears, and sometimes drive gears. These For Portable Electronic Readers gears typically have a long useful life and are not usu- ally replaced at major overhaul unless obvious damage is found. Gears rarely cause catastrophic engine failures.

OIL PUMP Failure of the oil pump is occasionally responsible for catastrophic engine failures. If oil pressure is lost, the engine will seize quite quickly. The oil pump is sim- ple, consisting of two gears in a close-tolerance housing, and it usually runs trouble-free. When trou- ble does occur it usually starts making metal long before complete failure occurs. Regular oil-fi lter inspection and oil analysis will normally detect oil pump problems long before the pump reaches the failure point. What's better than having Flight Guide airport data in your cockpit? How about Flight BEARINGS Guide airport data and IFR approach plates integrated with each airport! Introducing Bearing failure is responsible for a signifi cant Flight Guide eBooks now with IFR PilotPlates available for your portable Sony and number of catastrophic engine failures. Under Kindle DX Readers! Buy all three regions of both Flight Guide eBooks & IFR Pilot Plates, and together you will have yourself a suitcase full of printed IFR & VFR airport normal circumstances, bearings have a long useful data, in one portable light weight digital reader, for a fraction of the cost! life. They are always replaced at major overhaul, but it’s quite typical for bearings that are removed at To order go to www.flightguide.com/sowww.flightguide.com/sa • Airguide Publications, Inc. • 800 FLY-FLY1 (359-3591)

www.eaa.org 97 MIKE BUSCH

overhaul to be in excellent (sometimes even usually random failures unrelated to time major overhauls include new cylinders, so pristine) condition with little measurable between overhauls. age-related failures have become wear. Bearings fail prematurely for three quite rare. reasons: 1) they become contaminated with AND RINGS metal from some other failure; 2) they Piston and ring failures can cause cata- VALVES AND VALVE GUIDES become oil-starved when oil pressure is lost; strophic engine failures, usually involving As I discussed last month, it is quite common or 3) they become oil-starved because the only partial power loss but occasionally total for valves and guides (particularly exhaust) bearing shells shift position in the crankcase power loss. Piston and ring failures are of to develop problems well short of TBO. Valve saddles to the point where the bearings’ oil two types: 1) infant-mortality failures due to problems can usually be detected prior to supply holes become misaligned (“spun improper manufacture or installation; and 2) failure by means of compression tests, - bearing”). heat-distress failures caused by pre-ignition scope inspections, and surveillance with a Contamination failures can be prevented or destructive detonation events. Heat- digital engine monitor (provided the pilot by using a full-fl ow oil fi lter and inspecting distress failures can be caused by knows how to interpret the engine monitor the fi lter for metal on a regular basis. So long contaminated fuel or improper engine oper- data). If a valve fails completely, a signifi cant as the fi lter is changed before its fi ltering ation, but they are generally unrelated to power loss can occur. capacity is exceeded, particles of wear met- hours or years since overhaul. A digital als will be caught by the fi lter and won’t ROCKER ARMS AND PUSHRODS contaminate the bearings. If signifi cant Rocker arms and pushrods (which operate metal is found in the fi lter, the aircraft the valves) typically have a long useful life should be grounded until the source of the and are not routinely replaced at major over- metal is found and corrected. haul. ( bushings are always Oil-starvation failures are fairly rare. replaced at overhaul.) Rocker arm failure is Pilots tend to be well-trained to respond to quite rare. Pushrod failures are caused by loss of oil pressure by reducing power and stuck valves, and they can almost always be landing at the fi rst opportunity. Bearings avoided through repetitive valve inspections will continue to function properly even with and digital engine monitor usage as dis- fairly low oil pressure (for example, 10 psi). cussed earlier. Spun bearings experience infant-mortal- ity failures either shortly after an engine is MAGNETOS A severely spalled cam lobe. This camshaft failure overhauled (assembly error) or shortly after originated from corrosion pitting during an eight- Magneto failure is uncomfortably common- cylinder replacement. Failures can also month period of engine disuse. place. Fortunately, aircraft engines are occur after a long period of crankcase fret- equipped with dual magnetos for redun- ting (which is detectable through oil-fi lter engine monitor can usually detect pre-igni- dancy, and the probability of both magnetos inspection and oil analysis) or after extreme tion or destructive detonation episodes, failing simultaneously is extremely remote. cold starts without proper preheating. These allowing the pilot to take corrective action Mag checks during prefl ight run-up can are usually random failures, unrelated to before heat-distress damage occurs. detect gross magneto failures, but in-fl ight hours or years since overhaul. mag checks are far better at detecting subtle CYLINDERS or incipient failures. Digital engine monitors CONNECTING RODS Cylinder failures can cause catastrophic can reliably detect magneto failures in real failure is responsible for a engine failures, usually involving only partial time if the pilot knows how to interpret the signifi cant number of catastrophic engine power loss but occasionally total power loss. data. Magnetos should be disassembled, failures. When a rod fails in fl ight, it often A cylinder has a forged steel barrel mated to inspected, and serviced every 500 hours— punches a hole in the crankcase and causes an aluminum alloy head. Cylinder barrels doing so drastically reduces the likelihood of loss of engine oil and subsequent oil starva- normally wear slowly, and excessive wear is an in-fl ight magneto failure. tion. Rod failures have also been known to detected at annual inspection by means of result in camshaft breakage. The result is compression tests and borescope inspec- THE BOTTOM LINE invariably a rapid loss of engine power. tions. However, cylinder heads can suff er The bottom-end components of these Connecting rods usually have a long use- fatigue failures, and occasionally the head engines—crankcase, crankshaft, camshaft, ful life and are not normally replaced at can separate from the barrel, causing a cata- bearings, gears, oil pump, etc.—are very major overhaul. (The rod bearings, like all strophic engine failure. robust. They normally exhibit long useful bearings, are always replaced at overhaul.) failures can be infant-mortality related (due lives that are many times as long as recom- Many rod failures are infant-mortality fail- to improper manufacture) or age-related. mended TBOs. Most of these bottom-end ures caused by improper torque of the rod Age-related failures seldom occur unless the components (with the notable exception of cap bolts. Rod failures can also be caused by cylinder is operated for more than two or bearings) are reused at major overhaul and failure of the rod bearings, and these are three TBOs. Nowadays, most are not replaced on a routine basis. When

98 Sport Aviation March 2010 PHOTOGRAPHY BY MIKE BUSCH This photo shows the aftermath of a crank shaft failure on an IO-360. After the engine failure, the pilot safely landed the plane in a nearby fi eld. The cam shaft broke in half and the crankcase, as you can see, was ripped apart in fl ight. these items do fail prematurely, the failures engine.) It is not unusual for top-end com- are mostly infant-mortality failures that ponents to fail prior to TBO. However, occur shortly after engine manufacture, most of these failures can be prevented by rebuild, or overhaul, or they are random regular inspections (compression tests, failures that are unrelated to hours or years borescopy, etc.) and by use of digital engine since overhaul. The vast majority of ran- monitors (by pilots who have been taught dom failures can be detected long before how to interpret the data). Furthermore, they get bad enough to cause catastrophic when potential failures are detected, the engine failure simply by means of routine top-end components can be repaired or oil-fi lter inspection and laboratory oil anal- replaced quite easily without the need for FAA-PMA Manufacturer of Quality Aircraft Parts ysis. There seems to be no evidence that engine teardown. Once again, the failures www.mcfarlaneaviation.com/EAA these bottom-end components exhibit any are mostly infant-mortality failures or ran- 888.750.5244 sort of well-defi ned steep-slope wear-out dom failures that do not correlate with Dual for New! zone that would justify fi xed-interval over- time between overhauls. 912/914 Rotax Engines haul or replacement at TBO. The bottom line is that a detailed fail- Clean installation The top-end components—pistons, cyl- ure analysis of piston aircraft engines using without a clunky splitter box inders, valves, etc.—are considerably less RCM principles strongly suggests that Push to Unlock Controls robust. (The “top end” of a piston engine is what the airlines and military found to be Heavy duty for strength and long life analogous to the “hot section” of a turbine true about turbine aircraft engines is also Anodized aluminum knobs true of piston aircraft engines: The tradi- - Custom marking available tional practice of fi xed-interval overhaul or replacement is counterproductive. A con- Flight Control Cables & Engine Controls Custom made to your requirements scientiously applied program of • Same high quality as our FAA-PMA products on-condition maintenance that includes • Quick turn-around regular oil-fi lter inspections, oil analysis, compression tests, borescope inspections, and in-fl ight digital engine monitor usage can be expected to yield improved reliabil- Cowl Saver™ BafÀ e Seal Material ity and much-reduced maintenance Reduce Airframe Vibration & Stop Cowl Damage Free sample! expense and downtime. You can feel the difference! Magnetos are an exception. They really 10 times less friction need to go through a fi xed-interval major Exhaust valves often don’t survive to TBO. If we maintenance cycle every 500 hours, don’t catch a potential exhaust valve failure because we have no eff ective means of using compression tests, borescope inspections, View demo: www.mcfarlaneaviation.com/cowlsaver detecting potential magneto failures with- and engine monitor data, we risk a total failure McFarlane Aviation Products (“swallowed valve”). out disassembly inspection. 696 East 1700 Road, Baldwin City, Kansas 66006 Ph: 785.594.2741 Fax: 785.594.3922 [email protected]

PHOTOGRAPHY CONTRIBUTED BY MITCH ZEHR www.eaa.org 99 MIKE BUSCH

DON’T THEY GET IT? maintenance expense. Both engines on my condition with nothing to suggest that it It would take a lot of work for Lycoming or 1979 Cessna T310R are presently nearly 200 couldn’t have operated safely for another TCM to develop RCM-inspired mainte- percent of TBO and still operating fl awlessly. 1,000 hours. nance programs for our airframes and In 23 years of fl ying and maintaining my air- There’s an important lesson here: If you engines. Frankly, they have no incentive to plane, I’ve actually logged more post-TBO believe strongly in on-condition mainte- do this work. Even if they did, it would engine time than pre-TBO engine time. (And nance and your engine is “mature,” you’d be probably be an uphill struggle for them to by the way, none of the insurance carriers wise to explore the subject of on-condition get FAA approval because there’s so little I’ve used over those 23 years—USAIG, AIG, maintenance and past-TBO operation with operational data about piston aircraft and Starr—have the slightest problem with your inspection-authorized airframe and engines operated beyond current TBO rec- any of this.) powerplant mechanic before you authorize ommendations (because so few of them Sometimes it’s hard to persuade mechan- him or her to do an annual or 100-hour are). The Resnikoff Conundrum remains ics that it’s safe, sensible, and prudent to inspection. If you fi nd a maintenance philos- alive and well. continue an apparently healthy engine in ophy diff erent from yours, you might be wise Fortunately, as Part 91 operators, we service well beyond recommended TBO. A to choose another mechanic with inspection don’t have to overhaul our engines at the friend recently had a shop refuse to sign off authorization to do the inspection. manufacturer’s recommended TBO. There’s the annual inspection on his airplane nothing to prevent us from implementing because the engine was 300 hours past TBO. Mike Busch, EAA 740170, National Aviation our own RCM-inspired maintenance proto- The shop even refused to help the owner Maintenance Technician of the Year for 2008, has cols and maintaining our engines and obtain a ferry permit so he could fl y the air- been a pilot for more than 44 years and has airframes on-condition rather than on-time. plane to another shop to get a second logged 7,000 hours. He is a certifi cated fl ight I’ve been doing this for decades with my opinion! The result was both emotionally instructor and an airframe and powerplant own piston airplanes and have achieved and fi nancially stressful for the owner. The mechanic with inspection authorization. absolutely outstanding dispatch reliability engine was torn down by a big-name over- Questions for Mike may be e-mailed to coupled with drastically reduced haul shop that found it to be in pristine [email protected].

100 Sport Aviation March 2010