Incident Overview
The accident occurred while the airplane was cruising at 6,000 feet and encountered icing conditions. Air traffic control cleared the pilot to descend to 3,600 feet. During the descent, the pilot reported that one engine had lost all power and that the other engine was running rough.
Sequence of Events
The airplane continued descending. Approximately ten minutes later, the airplane departed controlled flight. It reversed its heading and impacted the terrain in a near-vertical attitude.
Post-Accident Examination
Examination of the left engine revealed that it had been feathered. Investigators found an induction duct that had deteriorated and begun to come apart. Foreign object material similar in appearance to the duct material was discovered in the compressor assembly. Additionally, the number five piston had a hole burned through it.
Probable Cause
The official probable cause was determined to be the pilot/mechanic's inadequate maintenance (inspection) of the aircraft and the pilot's failure to maintain airspeed (VMC). Contributing factors included icing conditions, deteriorated induction air ducting, and failure of a piston assembly.