What happened
The pilot reported that the aircraft was cruising at 11,000 feet when the engine began missing and losing power. Despite repeated attempts to restore normal operation, the engine did not recover. The pilot executed a forced landing in an open field. During the rollout, the nose wheel became lodged in soft sand, causing the aircraft to turn over.
The investigation
A post-accident examination of the engine revealed no compression in the number 1 cylinder. Further inspection determined that a valve had separated from its stem. The valve stem was found seized within the valve guide, which prevented proper seating and led to the loss of compression.
Findings
The mechanical failure originated in the number 1 cylinder's valve train. The separation of the valve and subsequent seizure of the stem caused an immediate loss of engine power. The pilot's inability to restore power necessitated a forced landing. The terrain conditions at the landing site contributed to the final orientation of the aircraft.
Safety message
Routine pre-flight inspections should include checks for loose hardware or signs of fatigue in engine components. Pilots should be aware that internal mechanical failures can occur without prior warning symptoms.