On Feb. 12, 2023, a Mooney M20K Encore sustained substantial damage when it was involved in an accident near Lakeway, Texas. The pilot was not injured in the crash.
The pilot reported that he had recently purchased the airplane and was relocating it to his home base at Outlaw Field Airport (KCKV) in Clarksville, Tennessee.
During the preflight inspection, he did not observe any anomalies. He reported that the airplane had 57 gallons of fuel onboard at takeoff and the engine oil was at a sufficient level for flight operations.
A review of ADS-B data showed that the airplane departed from Kestrel Airpark (1T7) in Spring Branch, Texas, and traveled to the northeast.
The pilot noted that while in flight, the engine had a low manifold pressure reading and then the engine sustained a total loss of power.
The ADS-B data showed that the airplane performed a 180° turn as it approached the Colorado River just to the north of Bee Cave, Texas. The pilot then maneuvered the airplane north toward Lakeway Airpark (3R9) in Lakeway, Texas.
Unable to make the airport, he performed a forced landing to a golf course just to the north of 3R9.
During the forced landing, the plane hit trees and a wood fence, then came to rest upright near a diesel generator, sustaining substantial damage to the fuselage and both wings.
An FAA inspector responded to the accident site.
A large amount of engine oil was observed trailing rearward on the underside of the fuselage. The engine oil level was checked at the accident site and oil was not observed on the dipstick.
Examination of the engine revealed a hole in the corner of the No. 6 piston, however the No. 6 cylinder was intact. The piston had eroded crown material and a darkened periphery. The engine case was found intact.
The top spark plugs from the Nos. 3, 5, and 6 cylinders and the bottom spark plugs from the Nos. 3 and 5 cylinders were found in a “worn out — normal condition.”
The right magneto timing was found at 22°. According to the engine manufacturer, it is supposed to be at 20°. The left magneto timing was found at 15°, rather than 20°.
The oil breather tube was found intact and the slot was not blocked. Engine oil was found splattered in and around the oil breather tube area, including traveling rearward on the area underneath the oil breather tube.
Before purchasing the plane, the pilot had an inspection performed by a mechanic.
One of the findings on the undated inspection list stated that “spark plugs are worn past limits.”
Additionally, all cylinders were borescoped and the cylinders were listed as “all appear normal.”
The pilot reported that there were no indications that the magneto timing was checked during the pre-buy inspection. He also told investigators that the airplane had been run with a lean mixture in the past.
A review of the engine maintenance records showed that the most recent time the spark plugs were cleaned and gapped, and the magneto timing was checked, was during a 100-hour inspection on Oct. 8, 2022, at 2,732.4 hours.
A review of data obtained from a J.P. Instruments EDM-700 onboard the airplane at the time of the accident showed an excessively high No. 6 cylinder head temperature reading about 17 minutes before the unit stopped recording data.
According to the FAA’s Pilot’s Handbook of Aeronautical Knowledge FAA-H-8083-25C, detonation is an uncontrolled, explosive ignition of the fuel-air mixture within the cylinder’s combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can lead to failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power.
Detonation is characterized by high cylinder head temperatures and is most likely to occur when operating at high power settings.
A common operational cause of detonation is listed as: Operation of the engine at high power settings with an excessively lean mixture.
This document also discusses preignition and states: Preignition occurs when the fuel-air mixture ignites prior to the engine’s normal ignition event. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage in the cylinder that causes a part to heat sufficiently to ignite the fuel-air charge.
Preignition causes the engine to lose power and produces high operating temperatures. As with detonation, preignition may also cause severe engine damage because the expanding gases exert excessive pressure on the piston while still on its compression stroke.
The document further discusses both detonation and preignition and states: Detonation and preignition often occur simultaneously and one may cause the other. Since either condition causes high engine temperature accompanied by a decrease in engine performance, it is often difficult to distinguish between the two. Using the recommended grade of fuel and operating the engine within its proper temperature, pressure, and RPM ranges reduce the chance of detonation or preignition.
Continental Motors published Mandatory Service Bulletin MSB94-8D Magneto to Engine Timing on Feb. 17, 2010, which discusses the importance of maintaining correct magneto timing and states: Incorrect timing, in addition to producing a rough running engine, can lead to detonation, preignition, and internal engine damage or failure.
Failure to properly maintain the magneto, harness, and spark plugs will lead to internal engine damage and failure.
Probable Cause: A total loss of engine power due to detonation and preignition in the No. 6 cylinder.
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This February 2023 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Strap on the timer to the spinner, it doesn’t lie 🤥
2° timing on one mag when the other is lagging is unlikely to cause detonation. This is likely a restriction in the #6 injector causing #6 to run lean at high MP cruise settings. I’ve seen this before, except the pilot saw what was happening and got it on the ground before the engine imploded, although it was already damaged from the detonation. There’s a very good chance this had happened before and is why the aircraft was for sale. Operating at a high MP in cruise would be a contributing factor, but the root cause is likely a restricted flow to #6 injector.
My arm chair, non-mechanic guess is that it wasn’t the mistimed magnetos that caused the engine failure, but more likely a long period of running at too high a power setting with too lean a mixture.
Turbocharged engines need to be babied. It’s tempting, when it’s possible to keep the manifold pressure high, to keep it high, especially in a “hot rod” airplane like the Mooney M20K. But reducing the MP to more common levels that a normally aspirated engine would have will reduce the stress and have a positive effect on engine longevity. Back when I was flying an M20K, I would reduce the power to 24 squared as soon as I got the airframe cleaned up on take off. There was no need to keep flogging it, as it climbed well on that power setting. It’s sort of a variation of the old saw, just because you can doesn’t mean you should.
A very good number of incompetent so called pilots don’t have a clue as to the theory of combustion and are just accidents waiting to happen! Every person holding a private pilots certificate or higher should have to take a good course in piston engine operations!
Seems the reports these days run off into some forlorn documents about this that and the other, mostly having nothing to do with the situation at hand.
Question; where exactly is the corner of a piston?
The burned location was about 30 degrees from the piston pin location.
In the docket, the materials lab report has a lot of pics.
From the docket, attachment 1 shows the JPI data.
At 15: 56 , cyl #1 and #3 are at 400 deg. #6 is 375
at 15: 58:08 , #1,#2 and #3 are over 400 deg and #6 is at 500 deg
at 15: 58:22 , #6 is over 600 deg and the TIT has dropped 300 deg.
It appears that this guy ‘cooked’ the engine…and caused the failure
No info on % power, cowl flaps position, mixture, turbo pressure…?
So, more stupid pilot tricks , and a wrecked newly acquires aircraft.!
If one magneto was set at 22 and the other at 15 degrees BTDC, it shows the difficulty of setting the timing accurately with the means that are typically used.
Since the average timing is at or blow the recommended timing, (20 degrees) this timing would not cause a problem!
The reality is: You cannot set the timing of a magneto with any accuracy using the common magneto timing tools.
It requires a dynamic test with a strobe light.
The “common magneto timing tools”, using the manufacturer’s specified procedures, have been proven over a period of more than one hundred years, for millions of engine hours.
Setting mags correctly is not a magicians trick. A competent aero mechanic should be able to do this operation with basic equipment. There no need to have fancy electronic gadget – they were not available 50 yrs ago and the timing of mags was successful back then.
It is necessary to use a ‘mag timing box’ to know when the breaker points open.
Even then, it’s difficult to get the timing within 1 degree.