Accident Overview
The airplane impacted flat desert terrain following an in-flight loss of control. A witness located about 1 mile south of the accident site heard a rough running engine and looked up to identify the source. As the aircraft passed overhead, the witness reported hearing the engine popping and backfiring for approximately 3 seconds, after which the engine stopped operating.
Witness Observations
The witness then observed the airplane dip to the right in a tumbling motion, describing it as a somersault with the nose dropping and the tail coming over the top. The aircraft completed about 2 to 3 revolutions over a duration of roughly 8 seconds before descending below tree level and colliding with the ground. The witness noted that it was somewhat cloudy in the area, but the airplane was below the clouds. Upon reaching the accident site to render assistance, the witness reported no frost or ice on the wings and stated that the ambient temperature was not cold enough for frost or ice formation.
Additional witnesses at the departure airport reported that the engine sounded as though the exhaust system was leaking severely, or that the exhaust or muffler was loose.
Engine Examination
An engine test run could not be performed due to displacement of the crankshaft caused by the nose-down impact. However, a subsequent engine teardown revealed no discrepancies in the engine core or its accessories that would have precluded normal operation.
Investigation Findings
The investigation did not establish a definitive cause for the engine roughness or failure. No evidence of pre-existing mechanical issues was found in the engine components. The witness descriptions indicate an in-flight loss of control following the engine stoppage, leading to the collision with terrain.