Accident Summary
Approximately three and a half hours after departure, while cruising at an altitude of 5,000 feet, the pilot heard a loud bang followed by extreme vibration of the airframe. The engine then experienced a total loss of power, accompanied by a slight smell of smoke. Air traffic control vectored the flight toward a nearby airport; however, due to the altitude and distance, the pilot determined that landing there was not possible. The pilot executed a ditching in a lake with full flaps deployed. After touchdown, the airplane became inverted. The pilot and one passenger successfully exited the submerged aircraft.
Aircraft Recovery and Initial Examination
The aircraft was subsequently recovered from the lake. Inspection revealed oil residue in the engine compartment and on the bottom skin of the fuselage.
Engine Failure Analysis
Detailed examination of the engine disclosed significant damage. The right side of the accessory case was displaced approximately two inches aft. The crankcase was fractured in the area from the No. 5 cylinder to the No. 6 cylinder. The crankshaft and the No. 6 cylinder connecting rod had fracture-separated. Further disassembly showed that the No. 5 main bearing saddle had separated from the crankcase and sustained heavy damage. The parting surfaces of the crankcase halves at the No. 4 main bearing position exhibited light fretting. The crankshaft was fractured at the rear No. 5 crankpin to counterweight cheek area.
Metallurgical examination of the fracture surface of the crankshaft revealed fatigue. No non-conformances could be found with the crankshaft or other associated components.
Engine History
The engine had accumulated approximately 296 hours since manufacture at the time of failure, as indicated by the aircraft’s recording tachometer. Review of maintenance records showed that the engine oil was last drained and serviced on September 25, 2001.