Accident Sequence
During the climb to cruise altitude, the pilot reported a power loss on one engine and received vectors to return to the departure airport. The pilot was subsequently cleared for the VOR-A approach and reported intercepting the inbound radial. The impact site was located to the right of the inbound radial and short of the extended runway centerline. Weather at the airport was visual flight rules (VFR). A post-impact fire damaged the airplane.
Examination
After the accident, the left engine propeller was found in the feather position. Visual and metallurgical examination confirmed that the turbocharger shaft had separated due to fatigue. The shaft contained chromium, though the aircraft overhaul manual states that "chrome plating...restoration of the shaft...are not permitted." Metallographics revealed a microstructure of grey iron, an automotive application, in the center housing. The turbocharger had been overhauled and installed on the left engine in October 1989. All three occupants were killed.
Probable Cause
The official probable cause was determined to be the pilot's failure to maintain airspeed during a single-engine approach, resulting in an inadvertent stall. Factors were a fatigue separation of a shaft in the left engine turbocharger due to the use of a Federal Aviation Administration approved overhaul procedure that was not consistent with the manufacturer's overhaul procedure, and the resultant loss of power to the left engine.