Primary finding
Probable cause
The loss of partial engine power during cruise for undetermined reasons. A contributing factor was the snow covered terrain.
Investigator assessment
Analysis narrative
The pilot said that his engine started running rough while flying over mountainous terrain. There was a large snow covered meadow beneath him, so he circled it while trying to resolve his engine problem. His attempts to regain full power were unsuccessful. The airplane was equipped with large tundra tires, and the pilot believed that a precautionary landing under partial power was more prudent than proceeding to the nearest airport while crossing mountain ridges and over flying the surrounding forest. During a wheel landing in the snow, the airplane nosed over and came to rest inverted. The forward section of the airframe, both wings spars, and the vertical stabilizer were bent. The reason for the partial power loss was undetermined.
Source record
Factual narrative
The pilot said that while flying over mountainous terrain, his engine started running rough. There was a large snow covered meadow beneath him, so he circled it while trying to resolve his engine problem. His attempts to regain full power were unsuccessful. The airplane was equipped with large tundra tires, and the pilot believed that a precautionary landing under partial power was more prudent than proceeding to the nearest airport while crossing mountain ridges and over flying the surrounding forest. During a wheel landing in the snow, the airplane nosed over and came to rest inverted. The forward section of the airframe, both wings spars, and the vertical stabilizer were bent. The reason for the partial power loss was undetermined.