Shortly after takeoff, the pilot advised air traffic control that he was returning to the airport due to low oil pressure. The engine subsequently lost power, and he was forced to land in a wheat field in Sheboygan, Wisconsin, five miles south of the airport.
During an on-site examination of the Mooney M20K, no oil was found in the crankcase, and subsequent examination of the engine and turbocharger revealed that the turbocharger was dry.
Further examination of the engine revealed evidence of preignition in the No. 5 cylinder that appeared to have been caused by failed spark plugs. The top and sides of the piston head were eroded, which allowed the exhaust gases caused by the preignition to pressurize the crankcase and force engine oil out of the breather tube.
Probable cause: Oil starvation due to preignition in the No. 5 cylinder as a result of failed spark plugs; the top and sides of the piston head were eroded, which allowed the exhaust gases caused by the preignition to pressurize the crankcase and force engine oil out of the breather tube.
NTSB Identification: CEN15LA279
This June 2015 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.
Neigher the NTSB Final report nor any documents in the NTSB Docket for this accident shed light on the root cause, i.e. WHY this aircraft engine lost effective firing of BOTH spark plugs in the number 5 cylinder. There’s a lot of nformation about the symptoms of this malfunction, and the outcome. Zip on the underlying cause. Perhaps someone with an A&P or IA background might add some meat to this discussion. The current report is about as informative as saying “my engine runs rough today…” So…??? Was there a problem with the ignition system? Injectors? Fuel? Leaning technique? Or ???? The aircraft was inspected just 13.7 hours prior to this catastrhopic failure. Why wasn’t an impending engine failure detected then?
“Why wasn’t an impending engine failure detected then?” perhaps because the condition didn’t exist at that point.
Now what concerns me is that both plugs failed. Did that failure happen after the piston was broached allowing oil into the combustion chamber? Probably not — I would guess that those plugs showed they were damaged by the detonation issues.
Could it have been a partly blocked injector causing this one cylinder to be in the detonation regime while the others were just fine?
At this point, I know of three injected (non-turbo charged) aircraft that have had partly blocked injectors, where the blockage was apparently caused by a substance commonly found in 100LL that under the right conditions will cause an injector to be partly to completely blocked.
The Lance that crashed off of Dekalb-Peachtree appears to have had this problem (NTSB Identification: ERA15FA208). The others had their injection systems torn down and re-assembled and they were then able to product 100% power.
I am also suspecting that the NTSB doesn’t take GA crashes like this very seriously. If they did, they would attempt to figure out what really happened. But that costs money and they do not want to put out that kind of investigation for something less than a Part 135 operator.