Cessna 150G N8465J accident near Corinth, Mississippi

Probable cause

The improper torque application on the crankshaft gear bolt by maintenance personnel during an engine overhaul, which resulted in the fatigue failure of the locking tab washer and gear alignment dowel and subsequent engine stoppage. Contributing to the accident was the operator’s exceedence of the engine overhaul calendar year limits recommended by the engine manufacturer.

NTSB analysis

According to the pilot, after about 2 hours of uneventful flight, a loud noise came from the engine compartment, the engine cowling shook violently, and the engine experienced a total loss of power. During the subsequent descent, the pilot attempted to restart the engine. The propeller continued to windmill, but the engine did not restart. The pilot selected a field for a forced landing, and during the landing roll, the landing gear became entangled with the crop. The airplane then nosed over and came to rest inverted, and the pilot and his wife egressed with minor injuries.

Examination of the engine revealed that the crankshaft gear bolt locking tab washer and the alignment dowel for the gear mounting flange were fractured due to fatigue. This allowed the gear to rotate on the crankshaft. The fatigue resulted from improper torque application on the crankshaft gear bolt during overhaul, which had been completed 26 years and 643 total airplane flight hours before the accident. In service bulletins and service instructions, the engine manufacturer warned that improper installation of the crankshaft gear may result in "complete engine stoppage" and recommended that engines be overhauled after 12 years in service, even if the engine had not accumulated the manufacturer-specified 2,000-hour time-between-overhaul during that period.

Text from the NTSB. Open the NTSB docket for ERA12LA574 for the full record.