Accident Sequence
The pilot had the waste gates on the turbochargers adjusted and intended to test fly the airplane following the work. After departure, the airplane reached an altitude of approximately 1,000 feet when witnesses heard an engine sputter. The airplane was observed making a left turn and entering a nose-low, left spin before impacting the terrain. The pilot, the sole occupant on board, was killed.
Engine Examination
A teardown of the left engine revealed that the exhaust valves in cylinders #3 and #5 were burnt through at the valve head. Additionally, the #5 exhaust valve had a deep preexisting mark on the valve stem. The failures of both valves were sufficient to cause a power failure in the left engine.
Probable Cause
The official probable cause of the accident was the pilot's improper emergency procedures and failure to maintain control of the airplane, which resulted in an inadvertent spin at too low an altitude to allow recovery. Factors in the accident were a power loss in the left engine as a result of the exhaust valve failures in cylinders #3 and #5.