Incident Overview
While conducting aerial spraying operations over a corn field, a pilot reported exiting the field and initiating a pull-up and turn to the east when a vibration was noticed. During the maneuver, oil from the number eight cylinder was observed leaking onto the engine exhaust. As the turn progressed to three-quarters completion, the engine's rocker arm shaft began to work its way out. The pilot noted that the engine was not developing power and decided to land on a north-south access road approximately 15 feet in width, with sides elevated roughly 2 feet in height.
Landing and Damage
During the landing attempt, the aircraft's left wing struck the wheat crop, causing the aircraft to rotate 180 degrees. Subsequently, the right landing gear separated from the aircraft. The aircraft continued in a rearward direction into the wheat field. The pilot reported that there had been an inch of rainfall the previous day.
Mechanical Findings
Post-incident examination revealed that the rocker arm bolt was fractured at the location of a cotter pin hole. The pilot had stated that the rocker arm shaft began to work its way out during the flight, consistent with the bolt failure.