Flight History
The pilot had flown the airplane once around the traffic pattern earlier that morning, following the removal and reinstallation of four of the six cylinders several days prior. No discrepancies were noted during that flight. A subsequent short positioning flight also proceeded without any issues.
Accident Sequence
The airplane departed on a chartered cargo flight. Shortly after takeoff, the engine suffered a partial loss of power, which quickly progressed to a complete loss. With unsuitable terrain ahead, the pilot ditched the airplane.
Engine Examination
After the airplane was recovered, an examination of the engine revealed that the crankshaft had failed aft of the No. 2 main bearing. The failure was attributed to fatigue followed by overload. Fretting was observed on both crankcase halves at the No. 2 main bearing saddle. The No. 2 main bearing was broken and extruded, and its saddle was also extruded. Additionally, the No. 3 main bearing halves were found to have shifted.
Maintenance Records
Review of the maintenance records indicated that overhauled cylinders had been installed at all positions in August 1996. At the time of the accident, the engine had accumulated 423 hours of operation since that overhaul.