Event Description
The pilot reported that, while in cruise flight at 2,500 feet with a private pilot flying the airplane, the engine began to run rough and shudder. The pilot stated, "I have the controls" and the private pilot responded, "you have the controls." The pilot then searched for a suitable forced landing area, observing a country road and a field. He completed the emergency checklist and entered a downwind leg to land on the highway. After turning base, he noticed power poles but could not see any power lines between them, leading him to decide to land in the field.
During a left 35-degree turn toward the field, the propeller struck a tree, causing the aircraft to yaw to the left and collide with the ground. The impact separated the landing gear and bent the engine firewall.
Examination Findings
Post-accident examination of the engine assembly revealed that the exhaust valve in the No. 4 cylinder had failed. Further inspection of the exhaust valve showed fatigue cracks that had propagated from opposite sides of the stem, adjacent to the beginning of the radius between the stem and the valve head.