AVwebFlash - Volume 13, Number 35b

August 30, 2007

By The AVweb Editorial Staff
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NASA Denies Reports of Drunken Astronauts

A NASA safety review has found no evidence to support claims that astronauts were impaired by alcohol when they flew in space, the agency said on Wednesday. Bryan O'Connor, NASA chief of safety and mission assurance, conducted the monthlong review to evaluate allegations in an Astronaut Health Care System Review Committee report that was released in late July. That report stated that in at least two instances astronauts had been so intoxicated prior to flight that flight surgeons and/or fellow astronauts raised concerns regarding flight safety, but the astronauts were still permitted to fly. O'Connor said he was unable to verify any case in which an astronaut was impaired on launch day, or any case where a manager disregarded the recommendation of a flight surgeon or crewmember that an astronaut should not fly the Shuttle.

"Should such a situation present itself in the future, I am confident that there are reasonable safeguards in place to prevent an impaired crewmember from boarding a spacecraft," O'Connor wrote.

No Charges For Men Who Tried To Get Into Airliner Cockpit

Winnipeg, Manitoba police say the actions of two men who made repeated attempts to get into the cockpit of a WestJet Boeing 737 while it was in flight from Calgary earlier this month was “not a reportable incident.” Canadian Pressreported Sunday that the two men insisted on seeing the cockpit while the aircraft was on the ground in Calgary and captain allowed them a brief visit and “showed them a few things,” said WestJet spokeswoman Gillian Bentley. "They took their seats and during the course of the flight, the two people involved did approach the flight attendant at the front of the aircraft, asking to go on the flight deck again, Bentley said. "She told them they could not. They were very nsistent.” Bentley said it took an intercom call from the captain behind the securely locked cockpit door to convince the men to return to their seats. Police met the pair on arrival and after a brief interview they were allowed to leave. Const. Jason Michalyshen said that because the two weren’t drunk, didn’t get physical and the plane wasn’t diverted there was no police action. Bentley said some passengers were upset by the incident but Bentley downplayed any suggestion of terrorism. "I don't think it had anything to do with hijacking. I think they just wanted to see the cockpit but there hasn't been any determination as to what their motives were," Bentley said.

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Cessna Sets Life Limit on Conquest; Airplanes Grounded in Australia

Operators of Cessna 441 Conquest II twin turboprops must comply with a life limit of 22,500 flying hours, Cessna has said, and several of the aircraft have been grounded. "As part of the continuing product safety process, Cessna looks at data from test articles and from field reports regarding the structural integrity of its aircraft," Cessna spokeswoman Pia Bergqvist told AVweb. Based on test and field data, Cessna has issued a Supplemental Inspection Document recommending the life limit for the aircraft. While most of the Conquests operating around the world are well below this limit, according to Bergqvist, several aircraft in Australia are beyond it, and those aircraft have been grounded. Australia's Civil Aviation Safety Authority has allowed one year for alternatives to be explored that could extend the safe operation of the Conquest beyond the current life limit. It's not known if any Conquests in the U.S. will be immediately affected, industry groups are looking into it.

AOPA spokesman Chris Dancy told AVweb his organization has been in contact with the Cessna Pilots Association but discussions are preliminary. The 441, a pressurized version of the 404, was first delivered in 1977. General-aviation aircraft certified under FAR Part 23 must have a life limit set by the manufacturer on critical structures such as wing spars, but an overall life limit is not required.

LSA Round-the-World Flight Completed

Two Indian Air Force officers have completed a circumnavigation of the globe in a Light Sport Aircraft in 79 days. Wing Commanders and Squadron Leaders Rahul Monga and Anil Kumar visited 19 countries in a Flight Design CTsw. The flight marks the 75th anniversary of the Indian Air Force. Monga and Kumar, who normally fly helicopters and fighter jets, launched June 1 from Delhi, India, and returned August 19, after flying through China, Russia, North America, Europe, and the Middle East. Monga flew solo across the north Atlantic so he could carry more fuel. "The round the world tour under day VFR rules was successful with this airplane despite difficult weather conditions," said Matthias Betsch, CEO of Flight Design, which is based in Germany.

"Of course, weather was a problem for us," Kumar told the Times of India. "We had to train ourselves to handle all kinds of problems ... we were sitting in the cockpit for nine or ten hours, moving from culture to culture, time zone to time zone. I think we are fortunate that we could cope up in all such situations." One of the first aircraft certified under the U.S. LSA standards, the CT is currently the best-selling LSA in the U.S., with 200 copies delivered.

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Eclipse 500 VLJ Draws $1.8 Million Bid on eBay

Eclipse Aviation CEO Vern Raburn announced at Oshkosh that one Eclipse 500 jet would be auctioned off on eBay and the owner could take it home right away, without having to wait until 2009 for their turn to come up. "We'll let the market decide what that could be worth," Raburn said, and this week, the company announced the results of its auction. Morten Wagner of Denmark placed the winning bid of $1,833,945 at 2 a.m. local time on August 11, outbidding five other contenders. Wagner plans to accept his Eclipse 500 in Albuquerque this week, the company said. "I was just sitting there, holding my breath, watching the auction run out," said Wagner. "When I saw I had won, I was delirious; I woke up the whole house and told everyone I just bought an aircraft on Eclipse's private marketplace."

Wagner, a 35-year-old internet entrepreneur, plans to use the jet for business travel throughout Europe, and to travel between his homes in London, Spain, and Denmark. Wagner is a pilot and currently flies a Cirrus SR22. "The fact that we can sell an early Eclipse 500 on an open market for more than $1.8 million demonstrates the enormous demand for very light jets," said Raburn.

Honeywell, Sensis Develop Runway Alerts for Pilots

It's fine for air traffic controllers to get conflict alerts when airplanes converge on the airport surface, but wouldn't it be better if that information was directly available to pilots? The cockpit technology to make that work is now available, Honeywell International and Sensis Corporation said this week. The two companies have created a cockpit advisory system that sends potential ground, arrival or departure conflicts directly to pilots as an audible alert. The system uses a Mode-S data link and an existing TCAS unit in the aircraft, and requires only software modifications to start working, the companies said. The audible alert is transmitted simultaneously to the cockpits in the affected aircraft and to air traffic controllers. Currently, surveillance equipment notifies air traffic controllers of potential incursions and then controllers must relay the information to pilots, slowing down response time.

"The cockpit advisory will ensure that pilots are aware of possible conflicts with the safe operation of their aircraft in the airport vicinity much quicker than current procedures and technology allows," said Rick Berckefeldt, Honeywell product marketing manager for safety and surveillance systems. "Only the pilots that may be involved in a potential conflict receive the audible cockpit warning, and advisories are only provided if a potential conflict is detected. With the audible alerts, no heads-down time is required for the pilots during critical approach, taxi and departure phases, helping to ensure a safe flight." The system was demonstrated this week at the FAA Interim Contractor Depot Level Support facility at Syracuse Hancock International Airport in New York.

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Fallout from Comair Crash Continues

It's been a year since a Comair crew tried to take off from the wrong runway in Lexington, Ky., and the co-pilot, who was the sole survivor, and the captain's widow have filed suits against the FAA, the airport, and Jeppesen. Also, the NTSB, which in its final report on the crash last month faulted the pilots for failing to check their position before takeoff, this week issued safety recommendations (PDF) asking the FAA to revise procedures for pilots and controllers. The FAA should require flight crews to positively confirm and cross-check the airplane's location at the assigned departure runway before crossing the hold-short line, the NTSB said. Also, controllers should not issue a takeoff clearance until after the airplane has crossed all intersecting runways, and controllers should refrain from performing administrative tasks, such as the traffic count, when moving aircraft are in the controller's area of responsibility, the board said.

First Officer James Polehinke suffered extensive injuries in the crash. The lawsuits allege that the FAA should have had two controllers on duty instead of just one, that the airport didn't do enough to clearly notify pilots of changes to taxiways during airport construction, and that Jeppesen was informed of the taxiway changes in June but didn't issue new maps until late in August, after the accident.

United Pilot Noticed for Niceness

While many general aviation pilots revel in avoiding the miseries of airline flight, most find themselves occasionally forced to join the milling crowds in the main terminals. But if they are lucky, they may find themselves aboard a United Air Lines flight captained by Denny Flanagan. Flanagan won his 15 minutes of fame this week when Wall Street Journal travel columnist Scott McCartney singled him out as an island of niceness amid a sea of mere bland competence. While other pilots may get you to your destination in one piece, Flanagan does that plus checks on your pets and your luggage, calls the parents of children flying alone to reassure them, invites families into the cockpit, makes jokes, raffles off free bottles of wine, and orders hamburgers for passengers during delays.

"I just treat everyone like it's the first flight they've ever flown," Flanagan told McCartney. "The customer deserves a good travel experience."

Balloon Pilot Says He Was Blown From Basket

A Canadian balloon pilot criticized by a passenger for being among the first out of burning balloon basket says he was blown out by what he suspects was the ignition of a fuel leak. Two people died and 11, including Pennock, were injured in the accident last week near Vancouver, B.C. Pennock was criticized by passenger Darlene Rutledge, who jumped 50 feet from the burning basket and questioned why the pilot was among the first out. She spoke with reporters from the hospital where she was recovering from burns and broken bones in her feet. In a story in the Vancouver Sun, Wednesday, pilot Steve Pennock says he remembers being thrown from the cockpit of the balloon after an explosion on board. He told the Sun he was thrown to the ground and temporarily immobilized. "I was blinded and stunned," he said. "I couldn't see or do anything I was basically disabled. I was shocked and stunned on the ground." Pennock said that once he was able, he helped get others out of the balloon but the fire burned through the tethers and it shot into the air. The basket, with Shannon Knackstedt and her grown daughter Gemma shot into the air before dropping from 400 feet into an RV park. Pennock said his actions were by the book. "I did exactly what would have been called for," he told the Sun. "I asked people to evacuate. The main concern is to get people out." Transport Canada and the Transportation Safety Board are investigating.

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Airport Videos Now in Google Earth

Users of the latest version of Google Earth, released last week, now can find videos related to all the world's airports with a single click. Version 4.2 enables users to embed videos and link them to sites on the world map, so the folks at planeplaces.com have collected all the airport-related videos at YouTube and linked to them to Google's map of the world. They found over 2,800 videos marked with airport identifiers. "We’re not claiming to have exhaustively searched YouTube or error-checked every video," they said. They have provided an e-mail link with each video and ask users to help weed out incorrect or inappropriate videos.

The video-map data can be downloaded from planeplaces.com and simply dropped into Google Earth. A random visit showed that the map is easy to use, with airplane icons indicating the sites with videos, and the videos load and play quickly. You're likely to find a random assortment of content, though, not all of it aviation-related, so patience is required.

A First Solo Cross-Country to Remember

We all remember our first solo flights but some are more memorable than others. A 69-year-old student on his first solo cross-country flight got lost last Sunday and stumbled into the busy airspace around Indianapolis International Airport. FAA spokesman Tony Molinaro told the Indianapolis Star that controllers tracked the plane flown by Keith Sharpe to within three miles of the airport and finally made contact with him. They directed him to land immediately. Three aircraft waiting to land circled the airport waiting for Sharpe's plane to clear the runway.

The Star says Sharpe told airport police he thought he was landing at Lafayette Airport and was trying to raise the Lafayette tower on the radio. Molinaro said that when contact was finally made (he didn't say how) the decision was made to bring him into Indianapolis. "We determined that if he wasn't sure where he was, we wanted to land him right away," he said. "We didn't want to take any chances with him being up in the air." The FAA is considering citing him for violating airspace regulations. Sharpe declined to comment to the Star about the incident.

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The Savvy Aviator #48: Reliability-Centered Maintenance (Part 2)

Mike Busch explores how RCM might be applied to our small airplanes and especially to our piston aircraft engines.

Click here for the full story.

For three decades, the airlines and military have been using the principles of reliability-centered maintenance to achieve drastic reductions in maintenance cost while actually improving reliability (discussed in last month's column). The lion's share of this improvement in maintenance cost-effectiveness has come from a major shift away from fixed overhaul, replacement or retirement intervals towards on-condition maintenance protocols.

Unfortunately, such RCM-inspired maintenance practices do not seem to have trickled down to the low end of the aviation food chain: piston-powered airplanes. Most aircraft owners dutifully overhaul or replace their piston aircraft engines when they reach TCM's or Lycoming's recommended TBO (at $20,000 to $35,000 a pop), even if the engines are running just fine with no signs of mechanical problems. They overhaul their propellers every five or six years because that's what Hartzell or McCauley recommends. Some operators overhaul or replace various airframe components at fixed intervals, regardless of condition, because that's what the aircraft service manual suggests. Some prophylactically replace vacuum pumps and alternators every 500 hours because some A&P told them it was a good idea.

Do such maintenance practices make sense? After analyzing reams of operational data from a number of major air carriers, RCM researchers concluded that fixed-interval overhaul or replacement rarely makes sense, and often makes things worse by increasing cost while decreasing reliability.

When Does TBO Make Sense?

For fixed-interval overhaul or replacement of a component to make sense, the component needs to have a failure pattern that looks something like the graph below, where the component can be expected to operate reliability for some fixed useful life, beyond which the probability of failure starts to increase rapidly to unacceptable levels.

Fixed-interval overhaul or replacement makes sense for components that have failure patterns that look like this.

Do our piston aircraft engines exhibit this kind of failure pattern? No, they do not. It's easy to demonstrate that these engines suffer the highest risk of catastrophic failure not when they pass TBO, but rather when they're fresh out of the TCM or Lycoming factory or a field overhaul shop. Take a look at these histograms derived from NTSB data on 180 engine-failure accidents for the five-year period from 2001 through 2005.

Small piston airplane accidents in 2001 through 2005 attributed by the NTSB to engine failure, by hours (top) and years (bottom) since engine overhaul. (Thanks to Dr. Nathan Ulrich for these graphs.)

This NTSB data can't tell us much about the risk of engine failure beyond TBO, because relatively few piston aircraft engines are allowed to remain in service beyond TBO (and we don't even have good data on how many are). What it does show quite clearly, however, is that engines fail with disturbing frequency during their first few years and few hundred hours in service after manufacture, rebuild or overhaul. The conventional wisdom is that our piston aircraft engines have a failure pattern that looks more like the following.

Piston aircraft engines are thought to have a failure pattern that looks like this.

This is the well-known "bathtub curve" in which the component exhibits a high risk of failure when first placed into service (so-called "infant mortality"), after which the probability of failure drops to a low level for the remainder of the component's useful life, then starts to rise again as the component is continued in service into the wear-out zone.

Does fixed-interval overhaul or replacement make sense for an engine with a bathtub-curve failure pattern? That's a tricky question, because engine overhaul at TBO becomes a two-edged sword. On one hand, it keeps us out of the presumptive wear-out zone where the probability of engine failure is thought to begin increasing toward unacceptable levels (although we don't have much data to support the contention that such an age-related wear-out zone actually exists). On the other hand, it puts us right back inside the infant mortality window where the data tells us clearly that the probability of engine failure is disturbingly high.

Would you be comfortable taking your family up in your piston-powered single-engine airplane with an engine at five hours since major overhaul (SMOH)? At night? Over rough terrain or water? In IMC? How about at 10 hours SMOH? Or 25 hours SMOH? (These are not easy questions.)

Does overhauling an apparently healthy engine at some fixed TBO help reliability more than it hurts? We can't be sure because there's so little data about the reliability of piston aircraft engines when they are operated beyond TBO (because so few of them are). But the evidence I've seen strongly suggests to me that fixed-interval overhaul for these engines doesn't make sense.

The fact that we have so little data about engines operated beyond TBO illustrates a major obstacle to the adoption of RCM-inspired on-condition maintenance in areas where fixed-interval overhaul has been the norm. RCM researchers call this "The Resnikoff Conundrum," which simply states that in order to collect failure data, there must be equipment failures. But failures of critical items such as engines is considered unacceptable because such failures can cause injury and death. This means that the maintenance program for a critical item must be designed without the benefit of failure data which the program is meant to avoid.

(The FAA's decades-long opposition to rescinding "the age 60 rule" for airline pilots is a perfect example of The Resnikoff Conundrum. Experts in aviation medicine have long been unanimous that there's no scientific basis for the FAA's venerable policy of forcing airline pilots to retire at age of 60. The FAA's longstanding argument has been that it has no safety data showing that allowing airline pilots to continue flying beyond age 60 is safe. Well, duh!)

We do know without doubt that fixed-interval overhaul is counterproductive for turbine aircraft engines, because the airlines and military started phasing out such fixed-interval overhauls in favor of on-condition maintenance decades ago. So we have tons of data about high-time turbine engines (some astonishingly high-time), and analysis of that data makes it crystal clear that fixed-interval overhaul hurts reliability more than it helps, not to mention that it greatly increases maintenance cost and downtime.

My experience and intuition leads me to believe that the same is true for piston aircraft engines, but we simply don't have enough operational data on very high-time piston engines to prove it.

Is This The Right Question?

Upon further reflection, I would argue that this isn't even the right question for us to be asking. That's because a piston aircraft engine isn't a single component with a single dominant failure mode and a well-defined failure pattern (like the bathtub curve). The NTSB reports reveal that engine failures occur for lots of different reasons. A piston engine is a complex system made up of hundreds of diverse components -- crankcase, crankshaft, camshaft, connecting rods, pistons, piston rings, cylinder barrels, cylinder heads, valves, valve guides, rocker arms, pushrods, gears, bearings, through-bolts, magnetos, spark plugs, etc. -- each of which has its own unique failure modes and patterns. An engine failure can be caused by the failure of any of these parts, and each of these parts has distinctively different failure characteristics.

To gain any real insight into how, when, and how often engines fail -- and how best to maintain the engine to prevent those failures -- we really need to analyze the failure modes and patterns of each of the engine's critical component parts, rather than try to lump them all into a single failure pattern for the engine as a whole.

Consider exhaust valves, for example. We know from experience that exhaust valves often don't survive to TBO. When they begin to fail, sometimes we're lucky enough to catch the potential failure at annual inspection before complete functional failure occurs (i.e., a "swallowed valve") by means of a compression test or borescope inspection. If the aircraft is equipped with a digital engine monitor and if the pilot knows how to interpret it, sometimes we can catch a potential exhaust valve failure before the valve fails completely. But if we're not lucky and the valve fails in-flight, it's usually a mayday situation and sometimes results in an off-airport landing or worse.

Does this mean that we should reduce engine TBO to something less than typical exhaust valve life? Should we be overhauling our engines every 500 or 1000 hours to prevent exhaust valve failures? Of course not!

Why not? For one thing, repairing a failing exhaust valve doesn't necessitate removing the engine from the airplane and tearing it down; the repair can be done simply by removing a cylinder. For another thing, we've got excellent tools (like borescopes and digital engine monitors) that allow us to reliably detect potential exhaust valve failures before complete failure occurs -- provided those tools are used properly and often enough. (I would estimate that the time between being able to detect a failing exhaust valve and it actually failing -- the P-F interval I mentioned last month -- is something on the order of 100 hours, which suggests that perhaps we should be inspecting the valves with a borescope every 50 hours -- especially in airplanes that are not equipped with a digital engine monitor.)

Failure Analysis

With this in mind, let's examine some of the most critical components of our piston aircraft engine, think about how those components fail and what consequences their failures have on engine operation, and what sort of maintenance actions we might take to deal with those failures in a manner that is both feasible and worth doing.


It's hard to think of a more serious piston engine failure mode than a crankshaft failure. The engine has only one crankshaft, and if it fails the engine stops producing power instantly and totally. Crankshaft failures result in safety consequences that we simply cannot tolerate.

Nevertheless, crankshafts are not normally replaced even at engine major overhaul. In fact, they are retired very rarely. Lycoming claims that their crankshafts typically remain in service for 14,000 hours and well over 50 calendar years! According to Lycoming, a crankshaft typically remains in service for 7,000 hours until it fails to pass dimensional tests at overhaul, whereupon the crankshaft is machined to approved undersize dimensions and continues in service for another 7,000 hours until it flunks dimensional tests at overhaul a second time. TCM hasn't published this sort of data about their crankshafts, but I would guess that TCM crankshafts experience a very similar life cycle.

There are three kinds of crankshaft failure: (1) infant-mortality failures due to improper material or manufacture; (2) failures following unreported prop strikes; and (3) failures secondary to oil starvation and/or bearing failure.

We've seen a rash of the first type of failures in recent years. Both TCM and Lycoming have had major recalls of crankshafts that were either forged from bad steel or were physically damaged during manufacture. These failures invariably occur within the first 200 hours after a newly manufactured crankshaft goes into service -- a classic infant-mortality failure. History shows that if a crankshaft survives the first 200 hours, we can be confident that it was manufactured correctly and should perform reliably for many engine TBOs.

The type 2 failures seem to be getting rare because owners and mechanics are becoming smarter about the high risk of operating an engine after a prop strike. Both TCM and Lycoming state that any incident that damages the propeller enough that it has to be removed for repair warrants an engine teardown inspection, including both magnetic particle and ultrasonic inspection of the crankshaft for surface and subsurface cracks. This applies even to prop damage that occurs when the engine isn't running. Insurance will pay for the teardown and any necessary repairs, no questions asked, so there's no reason for an owner to hesitate to do it and the risk of severe consequences if he does not.

That leaves us with type 3 failures due to oil starvation and/or bearing failure. We'll talk about these when we look at oil pumps and bearings.


Like crankshafts, crankcases are not usually replaced at major overhaul and often provide reliable service for many TBOs. However, if the crankcase remains in service long enough, it will eventually develop cracks. Some small cracks in low-stress areas of the crankcase are acceptable, but most crankcase cracks are considered airworthiness items that require the engine to be torn down.

The good news is that crankcase cracks tend to propagate quite slowly, so a detailed visual inspection once a year is generally considered to be sufficient to detect such cracks before they pose a threat to safety. Catastrophic engine failures caused by undetected crankcase cracks are extremely rare.

Although crankcases are not normally replaced at overhaul, they do go through a reconditioning process that involves honing the parting surfaces until they're perfectly flat and smooth, and then align-boring the crankshaft and camshaft journals. This process can only be repeated a finite number of times before the crankcase no longer meets dimensional specifications. So crankcases that do not develop fatigue cracks will be eventually retired for dimensional reasons. But their typical useful life is many TBOs.

Camshaft and Lifters

The interface between the cam lobes and lifter faces endures more pressure and friction than any other moving parts in the engine. The cam lobes and lifter faces must be extremely hard and perfectly smooth in order to function and survive. Even the slightest defects in these surfaces (such as tiny corrosion pits caused by periods of disuse or acid build-up in the oil) can lead to rapid destruction (spalling) of the cam and lifters, and the need for a premature teardown. Cam and lifter spalling is one of the most common reasons that engines fail to make TBO. This problem affects primarily owner-flown airplanes because they tend to be flown irregularly and to sit unflown for significant periods of time.

The good news is that camshaft and lifter problems seldom cause catastrophic engine failures. The engine will usually continue to make power even with severely spalled cam lobes and lifter faces that have lost quite a lot of metal, although there will be some loss of performance. Typically, the problem is discovered at an oil change when the oil filter is cut open and found to contain excessive amounts of ferrous metal shed by the destructing cam and lifters.

If the oil filter 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. The best way to prevent such failures is regular inspection of the oil filter (at least every 50 hours). Regular laboratory oil analysis may also be helpful in detecting such problems early.

If the engine is flown regularly so that the cam and lifters do not corrode or scuff, the cam and lifters can remain in pristine condition for thousands of hours. Many big-name overhaul shops routinely replace the cam and lifters with new ones at major overhaul, although some shops use reground cams and lifters.


The engine has lots of gears: crankshaft and camshaft gears, oil pump and fuel pump drive gears, magneto and accessory drive gears, prop governor drive gears and sometimes alternator drive gears. These gears typically have a very long useful life and are not usually replaced at major overhaul unless obvious damage is found. Gears almost never cause catastrophic engine failures.

Oil Pump

Failure of the oil pump is very occasionally responsible for catastrophic engine failures. If oil pressure is lost, the engine will seize quite quickly. The oil pump is a very simple gear pump, with one driven gear and one idler gear housed inside a close-tolerance housing. It is usually trouble-free, but when trouble does occur it usually starts making metal long before complete failure occurs. Regular oil filter inspection and oil analysis will normally detect oil pump problems long before they reach the failure point.


Bearing failure is responsible for a significant number of catastrophic engine failures. Under normal circumstances, bearings have a very long useful life. They are always replaced at major overhaul (it's required), but it's quite typical for bearings that are removed at overhaul to be in excellent condition with very little measurable wear. There are three types of reasons that bearings fail prematurely: (1) They become contaminated with metal from some other failure (e.g., cam/lifter spalling); (2) They become oil-starved when oil pressure is lost; or (3) They become oil starved because they shift position and their oil supply holes become misaligned ("spun bearing").

Type 1 failures (contamination) can mostly be prevented by using a full-flow oil filter, and inspecting the filter for metal on a regular basis. So long as the filter is changed before its filtering capacity is exceeded, particles of wear metals will be caught by the filter and won't contaminate the bearings. If a significant amount of metal is found in the filter, the engine should not be operated until the source of the metal is found and corrected, and checks performed to make sure the bearings haven't become contaminated.

Type 2 failures (loss of oil pressure) are fairly rare. Pilots tend to be well-trained to respond to loss of oil pressure by reducing power and landing at the first opportunity. Bearings will continue to function properly even with fairly low oil pressure (e.g., 10 psi).

Type 3 failures (spun bearings) are usually infant mortality failures, either shortly after an engine is overhauled (because the engine was not assembled properly), or shortly after cylinder replacement (because the crankshaft was rotated while the through-bolts were not torqued up, or the through-bolts were not properly re-torqued). They can also occur after a long period of crankcase fretting (which is typically detectable through oil filter inspection and oil analysis) or after extreme cold-starts without proper pre-heating.

Type 1 and 2 bearing failures are secondary to some other failure that contaminates or shuts off the bearing's oil supply. Type 3 bearing failures are primary, but usually unrelated to hours or years since overhaul.

Connecting Rods

Connecting rod failure is responsible for a significant number of catastrophic engine failures. When a connecting rod fails in flight, it often punches a hole in the crankcase and causes loss of engine oil and subsequent oil starvation. Rod failures have also been known to result in camshaft breakage. The result is invariably a rapid loss of engine power.

Connecting rods usually have a very long useful life, and are not normally replaced at major overhaul. (The connecting rod bearings, like all bearings, are always replaced at overhaul.) Many connecting rod failures are infant mortality failures caused by improper torquing of the rod cap bolts. Rod failures can also be caused by failure of the rod bearings (for the reasons discussed earlier under "bearings"), and these are usually unrelated to hours or years since overhaul.

Pistons and Rings

Piston and ring failures can cause catastrophic engine failures, usually involving only partial power loss but occasionally total power loss. Piston and ring failures are of two types: (1) infant mortality failures due to improper manufacture or installation; and (2) heat-distress failures caused by pre-ignition or destructive detonation events. Heat-distress failures can be caused by contaminated fuel or improper engine operation, but are unrelated to hours or years since overhaul. Use of a digital engine monitor can usually detect pre-ignition or destructive detonation episodes and allow the pilot to take corrective action before heat-distress damage occurs. Unless there's significant collateral damage, damaged pistons and rings can be replaced without engine removal or teardown.


Cylinder failures can cause catastrophic engine failures, usually involving only partial power loss but occasionally total power loss. Cylinders consist of a forged steel barrel mated to an aluminum alloy head. Cylinder barrels normally wear slowly, and excessive wear is detected at annual inspection by means of compression tests and borescope inspections. However, cylinder heads can suffer fatigue failures, and occasionally the head can separate from the barrel. Cylinders with worn barrels can be reconditioned using a number of processes (e.g., oversizing, plating, rebarreling) and kept in service for several engine TBOs. However, most big-name overhaul shops install new cylinders at major overhaul, with reconditioned cylinders used primarily for life extension. Cylinders can be repaired or replaced without engine removal or teardown.

Valves And Valve Guides

As discussed earlier, it is quite common for valves and guides (particularly exhaust valves and guides) to develop problems well short of TBO. Potential valve problems can usually be detected prior to complete failure by means of annual compression tests and borescope inspections, and continuously by means of a digital engine monitor (provided the pilot knows how to interpret the engine monitor data). If a valve fails completely, a significant power loss can occur that occasionally results in an off-airport landing. Failing valves and guides can be replaced without engine removal or teardown.

Rocker Arms And Pushrods

Rocker arms and pushrods (which operate the valves) typically have a very long useful life and are not routinely replaced at major overhaul. (Rocker arm bushings are always replaced at overhaul). Rocker arm failure is quite rare. Pushrod failures are caused by stuck valves, and can almost always be avoided through repetitive valve inspections and digital engine monitor usage as discussed earlier.


Magneto failure is actually uncomfortably commonplace. Fortunately, aircraft engines are equipped with dual magnetos for redundancy, and the probability of both magnetos failing simultaneously is extremely remote. Mag checks during pre-flight runup can detect gross magneto failures, but in-flight mag checks are far better at detecting subtle or incipient failures. Digital engine monitors can reliably detect magneto failures in real time if the pilot knows how to interpret the data. Magnetos should be disassembled, inspected, and serviced every 500 hours -- doing so drastically reduces the likelihood of an in-flight magneto failure.

The Bottom Line

After performing failure analysis of each critical engine component that has a history of contributing to catastrophic engine failure, I cannot help but be struck by some fundamental observations.

The "bottom-end" components of these engines -- crankcase, crankshaft, camshaft, bearings, gears, oil pump, etc. -- are very robust. They normally exhibit very long useful lives that are many times as long as recommended TBOs. Most of these bottom-end components (with the notable exception of bearings) are reused at major overhaul, and not replaced on a routine basis. When these items do fail prematurely, the failures are mostly infant-mortality failures that occur shortly after overhaul, or random failures that are unrelated to hours or years since overhaul. The vast majority of random failures can be detected long before they get bad enough to cause catastrophic engine failure simply by means of routine oil filter inspection and laboratory oil analysis. There seems to be no evidence that these bottom-end components exhibit any sort of well-defined wear-out zone that would justify fixed-interval overhaul or replacement at TBO.

The "top-end" components (or "hot section" components if you prefer) -- pistons, cylinders, valves, etc. -- are considerably less robust, and it is not unusual for them to fail prior to TBO. However, most of these failures can be prevented by regular inspections (compression tests, borescopy, etc.) and by use of digital engine monitors (by pilots who have been taught how to interpret the data). Furthermore, when potential failures are detected, the top-end components can be repaired or replaced quite easily without the need for engine removal or teardown. Once again, the failures are mostly infant-mortality failures or random failures that do not correlate with hours or years since overhaul.

The bottom line is that a detailed failure analysis of piston aircraft engines using RCM principles strongly suggests that what the airlines and military found to be true about turbine aircraft engines is also true of piston aircraft engines: the traditional practice of fixed-interval overhaul or replacement is counterproductive. A conscientiously applied program of on-condition maintenance that includes regular oil filter inspections, oil analysis, compression tests, borescope inspections and in-flight digital engine monitor usage can be expected to yield improved reliability and much reduced maintenance expense and downtime.

The only exception seems to be magnetos. They really need to go through a fixed-interval major maintenance cycle (not a major overhaul, but close) every 500 hours, because we have no effective means of detecting potential magneto failures without disassembly inspection. The good news is that we have two of them on each engine for redundancy.

Don't They Get It?

Why don't our airframe and engine manufacturers recommend RCM-based on-condition maintenance instead of very costly. fixed-interval. major overhauls? Well, for one thing, our TCM and Lycoming engines were certified under the old CAR 7 regulations that were developed long before RCM was invented. The same applies to the overwhelming majority of today's piston-powered GA airplanes, which were certified under the old CAR 3. Even for newer airplanes like the Cirrus, Columbia and Diamond, the manufacturers mostly specify time-directed maintenance (TDM) rather than condition-directed maintenance (CDM) because, unfortunately, there's no tradition of using RCM maintenance principles for small airplanes.

It would take a lot of engineering work for TCM and Lycoming to develop new RCM-inspired maintenance programs for our piston engines, and frankly they have very little incentive to do this work. Even if they did, it would probably be quite a struggle for them to get them approved by the FAA. After all, there's very little operational data about piston aircraft engines that are operated beyond current TBO recommendations (because so few of them are). The Resnikoff Conundrum remains alive and well in piston GA.

Fortunately, we Part 91 operators are under no regulatory obligation to overhaul our engines at the manufacturer's recommended TBO. There's nothing to prevent us from implementing our own RCM-inspired maintenance protocols, and to maintain our engines and airframes strictly on-condition rather than on-time. I've been doing this for decades with my own piston airplanes, and have achieved absolutely outstanding dispatch reliability coupled with drastically reduced maintenance expense. In 20 years of flying and maintaining my current airplane -- a turbocharged piston twin -- I've actually logged more post-TBO engine time than pre-TBO engine time.

Sometimes it's hard to persuade mechanics that it's safe, sensible and prudent to continue an apparently healthy engine in service well beyond recommended TBO. A good friend of mine recently had a shop refuse to sign off the annual inspection on his Cessna T310R (the same kind of airplane I fly) because his right engine was more than 300 hours past TBO. (I consider that engine a relative spring chicken, since both of my engines are -- as of September 2007 -- more than 800 hours past TBO and running great.) The shop even refused to help my friend obtain a ferry permit from the FSDO so he could fly the airplane to another shop to have the engine inspected! The result was both emotionally and financially stressful for the aircraft owner. Ultimately, his engine was torn down by a big-name overhaul shop, and nothing was found to suggest that the engine couldn't have operated safety for many more years and hundreds of hours.

There's an important lesson here: If you believe strongly in condition -directed maintenance (as I do) and your engine is "mature" (as mine are), you'd be wise to explore the subject of condition-directed maintenance and past-TBO operation with the chief inspector at your maintenance shop before you authorize him to commence an annual or 100-hour inspection. If you discover that his maintenance philosophy differs from yours, you might be wise to choose another shop to do the inspection.

See you next month.

Want to read more from Mike Busch? Check out the rest of his Savvy Aviator columns.
And use this link to send questions to Mike.


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On the Fly ...

Dr. Paul MacCready, whose Gossamer Albatross I became the first aircraft to fly across the English Channel under human power alone in 1979, died Aug. 28. MacCready was also the founder of AeroVironment, which developed groundbreaking alternative energy technology ... .

Boeing says it will be ready to test biofuel in a 747 within a year ... .

The Hawker 750 mid-size jet flew for the first time on August 23 ... .

The Hawker 900XP mid-size jet was type certified by the FAA last week, Hawker Beechcraft announced ... .

The Washington, D.C., ADIZ airspace changes shape on Thursday, August 30, AOPA has the details.

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We Need Your Help back to top 


AVweb has an opening for an able and experienced aviation writer and editor with proven experience in both print and web publishing, although we're willing to train the right person in the finer points of massaging content for the web. This position requires relocation to our Sarasota, Florida office. If this description fits you, contact aviationeditorial@comcast.net.

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Your Favorite FBOs back to top 

FBO of the Week: TNT Air (N47, Pottstown, PA)

Nominate an FBO | Rules | Tips | Questions | Winning FBOs

AVweb's "FBO of the Week" ribbon goes to TNT Air at N47 in Pottstown, Penn.

AVweb reader Howard Whyte recommended the FBO after an unscheduled stop at Pottstown:

Recently, while my wife and I were on a cross country flight to visit her brother, we experienced a complete electrical failure. We diverted to the nearest airport and upon landing discovered that because it was Sunday there were no services available. No rental cars, no maintenance and no way home. We called friends and we called acquaintenances, but no luck. Since we are based at N47 we finally called TNT Air. Tom and Angie Noetzel run the FBO there and they immediately sprang into action. Tom picked us up in a Cirrus 22 at no cost, and even let me fly it home. Angie met us on the ramp with cold bottled water and a welcoming smile. That's just the way the operate. Form setting up and hosting a lavish birthday party for a local 96 year old pilot to impromtu cook-outs they manage to keep the airport the place to be. Clean, hospitable, friendly, you couldn't ask for a better FBO than TNT Air.

Keep those nominations coming. For complete contest rules, click here.

AVweb is actively seeking out the best FBOs in the country and another one, submitted by you, will be spotlighted here next Monday!

Attention, LSA Builders & ROTAX 912 Engine Operators
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Picture of the Week back to top 

Picture of the Week: AVweb's Flying Photography Showcase

Submit a Photo | Rules | Tips | Questions | Past Winners

Each week, we go through dozens (and sometimes hundreds) of reader-submitted photos and pick the very best to share with you on Thursday mornings.  The top photos are featured on AVweb's home page, and one photo that stands above the others is awarded an AVweb baseball cap as our "Picture of the Week."  Want to see your photo on AVweb.com?  Click here to submit it to our weekly contest.


The good times continue here at "POTW" Central, with dozens more reader-submitted photos trickling in throughout the week.  Once again, we find ourselves in a tough spot trying to choose the best of the best to share with you here on AVweb.  Despite some tough calls, we've managed to narrow it down to a handful of don't-miss pics.  Let's dive in!

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Used with permission of Bill Howard

Last Plane Out of Santa Maria

Bill Howard of Milton-Freewater, Oregon shot this photo from the window of his airport hotel room — and now it's our "Picture of the Week."  In fact, this is the first "POTW" to feature a sunset in a while!

Watch your mailbox, Bill.  We'll be sending an official, sharp-as-a-tack new AVweb cap your way in the next few days.


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Used with permission of Mark Erwin

Watching the Skies

Mark Erwin of Menlo Park, California treats us to an emerging theme in this week's "POTW" submissions.  And despite what you're thinking, it's not the ATC tower — it's impending weather.


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Used with permission of Chris K. Shopperly

"One Day ..."

Chris K. Shopperly of Calgary, Alberta (Canada) snapped this one at AirVenture 2007, "my son's first trip to Oshkosh."

Next year, you guys stop by the AVweb booth and say hello, O.K.?


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Used with permission of Scott Gipson

Mustang Moment

Scott Gipson of Baytown, Texas submitted this photo on behalf of his son, Ryan Gipson.  Ryan is an Air Force Academy cadet (C3C) who captured this chilly scene on film "in March during a snow storm."


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Used with permission of
Dimitar Petkov Mahnev


Dimitar Petkov Mahnev of Assenovgrad, Plovdiv (Bulgaria) fires up the engines and prepares to fly us out this week.

Be sure to join us next Thursday morning for even more flying fun.  In the meantime, be sure to watch the "POTW" slideshow on AVweb's home page for more bonus images.

To enter next week's contest, click here.

A quick note for submitters:  If you've got several photos that you feel are "POTW" material, your best bet is to submit them one-a-week!  That gives your photos a greater chance of seeing print on AVweb, and it makes the selection process a little easier on us, too.  ;)

A Reminder About Copyrights: Please take a moment to consider the source of your image before submitting to our "Picture of the Week" contest. If you did not take the photo yourself, ask yourself if you are indeed authorized to release publication rights to AVweb. If you're uncertain, consult the POTW Rules or or send us an e-mail.

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Answer: Money

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Question of the Week back to top 

Question of the Week: Where Did You Fly This Summer?

This Week's Question | Previous Week's Answers


These days, it seems everyone in aviation is trying to bring young people into the fold, to the bolster the dwindling ranks of private pilots.  Last week, we asked which (of several options) holds the most promise for getting more young people involved.

Most of our readers thought targeted outreach programs (like the Young Eagles) can do more to spark interest in a new generation of pilots than anything else.  For the complete breakdown of options and reader responses, click here.
(You may be asked to register and answer, if you haven't already participated in this poll.)


This week, we're asking the old back-to-school standard:  What did you do on your summer vacation?  Or, more appropriately to AVweb, where did you fly this summer?

Click here to answer.

Have an idea for a new "Question of the Week"? Send your suggestions to .

This address is only for suggested "QOTW" questions, and not for "QOTW" answers or comments.
Use this form to send "QOTW" comments to our AVmail Editor.

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Names Behind the News back to top 

Meet the AVwebFlash Team

AVwebFlash is a twice-weekly summary of the latest news, articles, products, features, and events featured on AVweb, the internet's aviation magazine and news service.

The AVwebFlash team is:

Timothy Cole

Editorial Director, Aviation Publications
Paul Bertorelli

Russ Niles (bio)

Contributing Editors
Mary Grady (bio)
Glenn Pew (bio)

Features Editor
Kevin Lane-Cummings (bio)

Click here to send a letter to the editor. (Please let us know if your letter is not intended for publication.)

Comments or questions about the news should be sent here.

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If you're having trouble reading this newsletter in its HTML-rich format (or if you'd prefer a lighter, simpler format for your PDA or handheld device), there's also a text-only version of AVwebFlash. For complete instructions on making the switch, click here.

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