What happened
Approximately twenty minutes into the flight, the pilot reported a loss of engine power while cruising at 8,500 feet. Following the failure, the pilot maneuvered the aircraft through hilly terrain to select an appropriate area for a forced landing. After unsuccessful attempts to restore full engine power, the pilot commenced a final approach toward the selected site.
During this approach, the airplane collided with trees and subsequently impacted rapidly rising terrain. The impact caused the aircraft to catch on fire.
The investigation
Mechanical examination of the engine identified that the #4 intake valve was fractured and remained stuck in the open position. An analysis of the fracture face revealed multiple origins of fatigue. Furthermore, investigators discovered that the #4 valve guide was oversized by 0.030 inches.