NTSB Identification: CEN10FA521
14 CFR Part 91: General Aviation
Accident occurred Monday, September 06, 2010 in Caledonia, MI
Probable Cause Approval Date: 06/20/2011
Aircraft: CESSNA P210N, registration: N4632A
Injuries: 2 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

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.

Full narrative available

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