Cessna 150J N60290 accident near Lodi, California

Probable cause

A total loss of engine power during cruise flight due to a fatigue crack in the No. 3 cylinder connecting rod shaft resulting from either preignition or detonation, which resulted in a forced landing and impact with terrain.

NTSB analysis

The pilot receiving instruction and flight instructor had planned a local instructional flight on the day of the accident. Shortly into the flight after they reached their cruise flight altitude, they experienced a total loss of engine power. The airplane was substantially damaged during a forced landing in a field.

Postaccident examination of the engine revealed that the connecting rod shaft for the No. 3 cylinder had fractured due to fatigue cracking. The buildup of combustion deposits suggested the event was caused by either preignition or detonation or both, which would have been the result of the use of a lower grade fuel or operating the engine at high power settings with an excessively lean mixture.

Although a trace amount of automotive fuel was detected in the fuel line to the carburetor, fuel records indicate that the pilot had been using 100LL consistently. The operating fuel used by the previous owner is unknown; however, the previous owner implied that he used 100LL during conversations with the current owner. The pilot’s leaning practices showed that he regularly leaned the mixture to reach best rpm and enrichened three turns.

Text from the NTSB. Open the NTSB docket for WPR21LA121 for the full record.