Incident Overview
During the start of the right engine, the pilot heard two loud backfires or explosions. Simultaneously, he observed an area of the right wing expand upward. The passenger reported seeing flames emanating from the right wing. In response, the pilot shut down both engines.
Evacuation and Firefighting
The pilot and passenger evacuated the airplane without incident. Two observers on the scene attempted to fight the fire using handheld extinguishers. The local fire department was notified and arrived within four to five minutes, as stated by the fire department chief. The chief reported seeing a column of black smoke approximately 'a couple hundred feet' high.
Fire Dynamics and Damage
According to the fire department chief, the airplane was oriented with the nose facing north. The wind was from the west, which blew the flames away from the fuselage. The right wing, outboard of the engine nacelle, had collapsed to the ground. Wiring and melted structure were observed in the area between the nacelle and the wing. The top surfaces of the wing and the wingtip fuel tank were melted, and flames were seen coming from the melted areas as well as from the nacelle area.
Investigation Findings
Inspectors who examined the scene were unable to determine the source of the fire. A review of the airplane's maintenance records did not reveal any anomalies or pre-existing issues that could have contributed to the event. No official cause has been identified.