Beech C23 N6714E accident near Duncan, Oklahoma

Probable cause

A total loss of engine power due to the fatigue failure of the engine crankshaft. Contributing to the accident were the improper maintenance to the engine crankshaft, improper reassembly of the engine, and failure to follow the engine manufacturer's overhaul manual.

NTSB analysis

During the local flight, the airplane's engine began to violently shake and the pilot elected to shut down the engine and perform an emergency landing to a field. The airplane impacted a fence and terrain, which resulted in a bent firewall and left wing. A review of the maintenance records showed that, approximately 23 hours prior, the engine had experienced a loss of engine oil due to faulty maintenance during an annual inspection. The engine underwent maintenance and the airplane was returned to service. Examination and disassembly of the engine revealed that the crankshaft had fractured into 3 sections and that improper maintenance had been performed on several engine components. Metallurgical examination of the crankshaft revealed that the crankshaft had been improperly reworked which resulted in fatigue and crankshaft failure. The crankshaft rework and engine reassembly did not follow the manufacturer's overhaul manual.

Text from the NTSB. Open the NTSB docket for DEN08LA163 for the full record.