What happened
During a return leg of a 14 CFR Part 135 sightseeing operation from the Grand Canyon to Scottsdale, Arizona, the pilot reported a sudden loss of engine power. At the time of the incident, all other instrument readings appeared normal. The pilot attempted standard troubleshooting procedures by enriching the fuel mixture and switching fuel tanks, but these actions did not restore power.
The pilot decided to divert to Pulliam Airport (FLG) in Flagstaff, Arizona. Shortly after turning toward the airport, smoke began entering the cabin from beneath the instrument panel. The pilot secured all electrical power, which caused the smoke to diminish temporarily. However, shortly thereafter, the engine lost additional power and the cabin filled with smoke again. Unable to reach the airport, the pilot elected to land in an open field.
During the landing roll, the aircraft struck three fence lines and a dirt embankment. The flight phase was identified as en route sightseeing when the failure occurred.
The investigation
A post-accident examination of the engine revealed significant mechanical failures. The aft attachment exhaust studs on cylinder number one had sheared off completely. Additionally, the forward stud attachment nuts were found to be loose. These mechanical issues directly correlated with the reported power loss and subsequent smoke intrusion into the cabin.
Findings
The investigation determined that the primary cause of the accident was the failure of the exhaust system components. The shearing of the studs and the loosening of the nuts led to a loss of engine performance and the introduction of smoke into the cockpit area, forcing an emergency landing in unprepared terrain.