Cessna P210N N4632A accident near Caledonia, Michigan

Probable cause

A loss of engine power as a result of a fatigue failure of the crankshaft due to the loss of engine case through-bolt torque. Contributing to the accident was a mechanic's use of incorrect hardware.

NTSB analysis

The pilot and certified flight instructor were in a holding pattern during an instrument proficiency check when they heard a bang from the airplane's engine area. They initiated a forced landing and the airplane impacted terrain at the base of a hill. Fuel leaked and a ground fire ensued, resulting in substantial damage to the left wing. No airframe preimpact anomalies were observed on-scene. An engine teardown inspection revealed a separation of the crankshaft No. 3 short cheek consistent with fatigue. Additionally, the No. 2 lower through-bolt had the lowest torque value of all bolts and incorrect hardware was used on that through-bolt. Fretting was observed on the mating surfaces of the main bearing supports near the No. 2 through-bolt and its bearing had spun out of its support. Engine logbook entries indicated a mechanic replaced cylinders that would have required the removal and installation of hardware on the No. 2 through-bolt, approximately 19 months prior to the accident.

Text from the NTSB. Open the NTSB docket for CEN10FA521 for the full record.