What happened
While operating in cruise flight at 2,500 feet, the pilot experienced an engine malfunction characterized by rough running and shuddering. After confirming control of the aircraft, the pilot searched for a suitable area for a forced landing and identified both a country road and a field as potential options.
The pilot completed the emergency checklist and initiated a downwind pattern to land on the highway. During the base leg of the approach, the pilot observed power poles but could not identify any power lines between them. Consequently, the pilot decided to divert to a nearby field. While executing a left 35-degree turn toward the field, the propeller struck a tree. This impact caused the aircraft to yaw to the left and collide with the ground, resulting in the separation of the landing gear and damage to the engine firewall.
The investigation
An examination of the engine assembly was conducted following the accident. Investigators found that the exhaust valve in the No. 4 cylinder had failed. Further inspection of the exhaust valve revealed that fatigue cracks had propagated from opposite sides of the stem, specifically at the beginning of the radius between the stem and the valve head.