Accident Cessna P210N N4632A, Monday 6 September 2010

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Date:	Monday 6 September 2010
Time:	07:45 LT
Type:	Cessna P210N
Owner/operator:	Centurion Aviation LLC
Registration:	N4632A
MSN:	P21000810
Year of manufacture:	1982
Total airframe hrs:	4342 hours
Engine model:	Continental TSIO-520-RCAF
Fatalities:	Fatalities: 0 / Occupants: 2
Other fatalities:	0
Aircraft damage:	Substantial
Category:	Accident
Location:	Caledonia, Michigan - United States of America
Phase:	Manoeuvring (airshow, firefighting, ag.ops.)
Nature:	Training
Departure airport:	Grand Rapids-Gerald R. Ford International Airport, MI (GRR/KGRR)
Destination airport:	Grand Rapids-Gerald R. Ford International Airport, MI (GRR/KGRR)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
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.

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.

Accident investigation: