What happened
Following maintenance work involving the adjustment of the turbocharger waste gates, the pilot attempted a test flight to verify the aircraft's performance. Shortly after departing, the aircraft climbed to an altitude of approximately 1,000 feet. During this climb, observers noted the engine began to sputter. The aircraft then executed a left turn and transitioned into a nose-low, left-hand spin, eventually impacting the terrain.
There was one fatality resulting from the accident, as the pilot was the only person on board the aircraft.
Findings
An investigation and subsequent teardown of the left engine identified critical failures within the engine components. Specifically, the exhaust valves in cylinders #3 and #5 were found to be burnt through at the valve head. Additionally, a significant pre-existing mark was discovered on the valve stem of the #5 exhaust valve. The investigation concluded that the failure of these two valves caused a loss of power in the left engine, leading to the loss of control.