By Lisa Turner, EAA Lifetime 509911
This story first ran in the November 2019 issue of EAA Sport Aviation.
I was over a swamp when the engine started to burble. That’s a scientific word for “make a strange extra noise that strikes unease into a pilot’s heart.”
I’m making this up, I thought. Everything is fine.
Then the engine stopped.
Okay, I didn’t make it up.
Switch tanks. Fuel pump on. Restart. Check fuel pressure and quantity.
The engine jumped back to life in a totally normal manner, with absolutely no fear-producing murmurs or burbling noises. Upon landing at the nearest airport, a check of all systems revealed the dratted clogged fuel filter on the left tank.
Why didn’t I think to check that earlier?
It could have ended differently.
A week later, a friend named Tom was flying over the beach on the east coast of Florida in his newly restored Stearman. He heard a loud bang and then oil began to streak the windscreen. He put the unhappy beast down on the hard-packed beach sand in front of a set of condos. There wasn’t a soul anywhere on the glistening stretch of beach, and the landing was uneventful, except for the security personnel who streamed out of the private oceanfront club.
Careful not to slip in the oil coating the aircraft, Tom exited the cockpit and took a look at the engine. It had blown a lower cylinder. After extensive disassembly and trailering, Tom got the Stearman back to his hangar and sent the engine off for repair.
“It had a bent rod from a hydraulic lock start,” the man on the other end of the phone said.
“But I was careful to clear it before starting.”
“Well, somebody wasn’t careful before you got your engine,” the man said in a matter-of-fact tone.
What causes an engine to fail? Is there anything you can do to prevent it? Engines don’t just fail out of the blue, although it certainly feels like it when you’re the one piloting and it happens to you.
Amidst the numerous discussions about everything airplane at EAA AirVenture Oshkosh, one of them was mechanics and owners talking about engine failures. After processing the information, I’ve come up with some actions we can take to make these failures less likely. I’ve included some general engine failure statistics from the 27th Joseph T. Nall Report.
According to the Nall report, 73.8 percent of all noncommercial fixed-wing GA accidents were attributable to pilot error, 15.7 percent to mechanical failure, and the rest to “other or unknown.” Some good news is that the accident rates continue to go down, albeit slowly and in fits and starts. The relatively low rate of mechanical failures means that if we spend a little more time addressing them, we can get the accidents down further.
Engines in Homebuilt Aircraft
The No. 1 reason for failure in the first 100 hours is actually not the engine. It’s the installation or operation of the engine. No matter if it’s a Rotax, Continental, Hirth, or other brand, defects in new or rebuilt flat engines are rare. Mistakes are being made in installation and system hookups.
As a subset of the top reason for engine failure in homebuilts, fuel system design, hookups, and operation cause many of the failures in the first 100 hours.
What you can do: Use the EAA Flight Test Manual. Use the test cards and add as much rigor as you can to the checklists, hookups, manufacturer’s instructions, and any other data you can look at before test flying your airplane. Get A&P mechanics and technical counselors to look at your installation and workmanship. Don’t let your guard down after your 25- or 40-hour test period. The excitement of flying will woo you, and you’ll start assuming that everything is just fine and will stay that way.
Engines in Production Aircraft
The top reasons for an engine to quit in a production aircraft are fuel exhaustion, fuel starvation, fuel contamination, and carburetor icing. This should actually be good news since they are all somewhat controllable. Fuel venting, where something plugged the vent and stopped flow, is also included here.
After fuel problems are the miscellaneous areas reflecting engine condition neglect: bearings, connecting rods, valves, pistons and rings, and system failures. Corrosion from sitting idle is a factor, as are incorrect operation and overheating. Most of these developing problems will warn you ahead of time if you’re attentive.
What you can do: Work on eliminating the human-caused factors. We studied these in training, and it doesn’t hurt to go back and review flight planning and fuel management. Good planning and thorough inspections are important.
Learn all you can about your specific engine. Know exactly what your engine calls for on a preflight and how it acts on the runup. Use an engine monitor plus other engine health indicators to tell you exactly what is happening in your engine when you fly. Use oil analysis, detailed visual inspections on the ground, and a fine-tuned ear in the air. Be the engine whisperer.
Two-Stroke Engines
Lighter, cheaper, and more power in a small footprint give two-stroke engines a great profile for light aircraft. Or not? Some pilots say they will never get into the air in a two-stroke powered aircraft, assuming that the engine will look and behave like their lawn mower.
While we will never end the animated discussion over reliability, the fact is that high-quality two-stroke engines such as Rotax and Hirth fill an important spot in ultralight and light-sport flying. Mechanical simplicity, power-to-weight benefits, and low cost drive this market.
On some two-stroke engines, there is a tag that warns, “Do Not Use on Aircraft. Engine is Subject to Sudden Stoppage.” When a two-stroke stops, it stops with little warning and feels like it was twilight-zone induced. And even though the engines themselves are simple, it just feels as if there is more that can go wrong.
The top reason for two-stroke engine failure is not following operating procedures — improper fuel/oil mix (seizure) and fuel contamination, exhaustion, and starvation.
What you can do: Follow all of the manufacturer recommendations for servicing, overhaul, and operation. Pay extra attention to the fuel/oil mix, whether it’s manual or injected, and don’t let the engine sit idle for months at a time without following storage steps. Be ready for a failure in flight and know exactly what you’re going to do to land safely. When properly cared for, two-stroke engines are highly reliable. They are just a little more susceptible to neglect.
Radial Engines
The top cause for engine failure in a radial is from improper starting procedures. This can lead to a partial hydraulic lock that is not identified at the time and shows up later in flight as an engine failure. This type of failure can be sudden and highly damaging.
What you can do: Get intimate with your engine. Include a thorough preflight examination of the cylinder studs and surrounding areas, looking for thin, dark cracks and oil seepage. In the story that began this article, the owner didn’t know that the engine had been mistreated prior to being installed and wasn’t sure what to look for. Any time a radial engine is shut down for a length of time, oil can drain into the lower cylinders. Since oil is incompressible, as the piston approaches top dead center and both valves close, the oil can physically stop the piston. If forced, a little or a lot of damage can occur. This can manifest itself as a loosened cylinder, a bent rod, or loose spark plug inserts.
Prevent this from happening by following the exact start procedures for the engine. Typically, this involves turning the prop through by hand (ignition off) to feel for a lock so you can clear it. This requires attention and experience. Some pilots with plenty of experience can bump the starter from the cockpit and feel for hydraulic lock. The remedy if you find a lock? Pull the spark plug(s) and drain the offending cylinder(s).
Tips for Continued Engine Health
Install and operate your engine according to service instructions, bulletins, airworthiness directives, and other instructions for continued airworthiness.
Avoid letting the airplane sit for long periods of time without flying. If it is going to sit for the winter, use the opportunity to service it and then store it in a condition that will preserve the components.
Learn as much as you possibly can about the engine you have and use ongoing engine monitoring to understand its condition on every flight. Make sure the alarm parameters are set correctly for the engine (EGTs, CHTs, pressures, etc.). Regular inspections should include differential compression testing with a borescope and in-depth trend analysis. In his book Mike Busch on Engines, Mike goes into great detail about all the things you can do to keep your engine healthy.
Smooth aircraft operation will also extend the life of aircraft components. In the August 2019 edition of EAA Sport Aviation, Steve Krog in “Jerky Driver or Smooth Aviator” wrote, “Smooth, coordinated inputs will make for a better, safer flight, with a lot less wear and tear on your airplane.” This is especially true with engines.
Engine failures are rare to begin with. Follow these tips and make them even rarer. And realize that the most likely time for an engine to fail is right after it’s been returned to service or right after it has been installed in a new aircraft.
Lisa Turner, EAA Lifetime 509911, is a manufacturing engineer, A&P, technical counselor, flight advisor, and former designated airworthiness representative. She built and flew a Pulsar XP and Kolb Mark III, and is currently restoring a Waco UPF-7 with her husband. Lisa is a member of the EAA Homebuilt Aircraft Council and Women in Aviation International. For more from Lisa, check out her column Airworthy every month in EAA Sport Aviation.