Some Thoughts On Engine Reliability

"I understand you deliver little airplanes to Australia. How long does that take? Two days? I came back from Sydney on a Qantas 747 last year, and that was a real grind---13 hours nonstop." Some of those folks are amazed when I tell them I rarely fly jets. My rides are more typically single- and twin-engine piston and turboprop aircraft that can require as long as a week to make the trip Down Under.

Many can't believe it's possible to fly a single-engine piston airplane across an ocean. "Wouldn't it be easier and safer to just put the airplane in a pallet and ship it? How many times have you had to ditch?"

When I tell them, "Never," they're understandably skeptical. Problem is, if I say the same thing to a group of pilots, even some of them don't believe me.

The myth is that engines quit all the time in "those little airplanes." After all, many newspaper accounts of aircraft accidents read like amateur night in the sky. "A light plane crashed in an open field on Sunday, only 17 miles from a school yard where middle-school children might have been playing if it hadn't been late July. The accident site was also only 235 miles from a nuclear powerplant that was closed in 1995. The plane, a single-engine Cherokee Skylane, made a successful landing as the pilot apparently remembered to extend the landing gear at the last second, but both propellers were nevertheless damaged. Both occupants escaped injury, and there was little other damage to the eight-seat aircraft (that wasn't equipped with a parachute). The FAA confirmed the pilot had not received a weather briefing for his planned 78-mile flight and had not filed a flight plan, so he had no idea where he was."

That's certainly one reason why many intelligent non-pilots, not intending any insult, almost always first ask the same question, "What do you do if the engine quits?" Pilots who read the brand of uninformed journalism above would keel over with laughter if it weren't for the fact that many people accept such ludicrous newspaper accounts as factual.

The reality is, if you do everything right and don't contribute to your own engine failure, chances are you'll never have one. The catchphrase above is, "Do everything right."

How many times have we read news accounts of an airplane that ran out of fuel two miles short of the runway after overflying a dozen possible landing sites? Or what about aircraft that lost power when an improperly secured oil cap came loose, and all the oil drained away, and the engine shut down for lack of lubrication?

The number of ways pilots can contribute to their own downfall is practically legend, and in this case, we're only considering engine failure.

Fortunately, that doesn't have to be the case. Properly maintained and operated aircraft engines are almost unbelievably durable. In many respects, they're more reliable than automotive engines. Most pilots will fly their entire lives without a murmur of complaint from the Lycoming/Continental/Jacobs/Pratt & Whitney out front.

To better appreciate the reliability of general aviation engines, we contacted Victor Sloan of Victor Aviation in Palo Alto, Calif. Sloan's technicians produce about 150 overhauled Lycoming and Continental powerplants each year, all balanced, blueprinted and cryogenically treated to minimize heat and vibration and deliver consistent power. Sloan's XR Black Edition VII engines have become a standard against which many overhaulers and original equipment manufacturers measure their products.

We asked Sloan about piston-engine reliability. He said, "Most people analogize aircraft engines to automotive engines, and aircraft powerplants will nearly always come out ahead in any comparison of reliability, if not technology. A standard Lycoming IO-360-A1A rated for 200 hp, for example, carries a TBO of 2,000 hours, and contrary to what you might imagine, that's not an unrealistic number if the engine is built correctly, flown often and treated properly with periodic servicing." Convert those hours to nm in a Cardinal RG or Mooney 201 at 150 knots, and it works out to roughly 300,000 nm. How many cars do you know that will run that far on their original engine?

Sloan also feels the difference in how automotive and aircraft engines are operated gives aircraft mills the edge. "While it's true most auto engines are rarely called on to deliver full power, they're usually revving up and down on most trips, and that generates stress. An aircraft engine is designed to deliver brief periods of full power, then run at 65% to 75% power all day long, and many of them do that very well on ferry flights across the Atlantic and Pacific."

When I asked him if there was one over-riding mistake that damages engines more than others, he responded, "Heat is the nemesis of all piston engines. Some pilots don't truly appreciate the importance of maintaining cylinder head temps at or below 380 degrees, either by use of cowl flaps, an adequately rich (or lean) mixture or lowering the nose to put more air through the cowling. Aircraft piston engines are constructed with a variety of metals, and each expands and contracts with a different heat coefficient. Even lean-of-peak operation is acceptable on many engine models as long as you maintain power settings and temperatures within limits.

"A CHT of 340 to 380 degrees is fairly optimum for most aircraft engines," Sloan continues. "Shock cooling is also tough on an engine, again because of the rate of contraction of different metals. If you can maintain the CHT at 350 degrees or more throughout every flight, you'll have a better chance of making your engine last well past TBO."

Sloan feels a proper warmup and cool­down are extremely important, too, especially in the big-bore Lycomings and Continentals. "An oil temperature of at least 100 degrees is essential before you apply run-up power if you hope to make it to TBO," says Sloan. "It's also a good idea to allow even a normally aspirated engine to cool down before you pull the mixture to idle/cutoff. There's no specific interval to worry about as there is with a turbo, usually three to five minutes, but any engine benefits from a minute or two to let things cool and settle down after delivering power.

"Similarly, shock cooling or shock heating can induce stress on engine components and cause premature fatigue," Sloan explains. "A number of advanced heat dissipation processes are available, such as high-emissivity electrostatic black powder coating, high-temperature ceramics and isotropic internal parts finishing. Unfortunately, these processes are not yet available through the engine manufacturers.

"A high frequency of engine use and intelligent cycling of engine power can also enhance engine life," says the engine overhaul expert. "Air show legend Bob Hoover is living proof of the concept. His big Shrike Commander was truly a working airplane, often flying 1,000 miles or more every week between air show venues. Hoover flew his two turbocharged Lycoming engines to TBO three times, flying 380 air shows without any major problems." Hoover retired his Commander to the National Air & Space Museum, Udvar-Hazy Center in Chantilly, Va.

In other words, run your engine by the book, change the oil regularly, avoid conditions that might overheat it and fly as frequently as possible, and you, too, may someday have your airplane enshrined at the Smithsonian.