Incident Overview
During a flight, a pilot observed a decrease in oil pressure and decided to divert to an alternate airport. While en route, the oil pressure dropped completely, prompting the pilot to execute an emergency landing in an open field. As the aircraft rolled to a stop, it encountered a soft spot in the terrain and nosed over.
Post-Incident Examination
An examination of the engine revealed a dimple and a hole in the rocker box cover of the No. 3 cylinder. Inside the rocker box cover, investigators found a loose 3/8-24 hexagon jam nut, which was identified as belonging to the intake rocker arm adjusting screw. The hole and dimple were located opposite the exhaust rocker arm adjusting screw and matched the size and shape of the loose nut.
Sequence of Events
The pilot initially noticed a decrease in oil pressure and made the decision to land at an alternate airport. However, before reaching that airport, the oil pressure was completely lost, necessitating an immediate emergency landing. The landing was made in an open field, and during the landing roll, the aircraft struck a soft area, causing it to nose over.
Findings
The investigation confirmed that the hole and dimple in the rocker box cover were caused by the loose jam nut, which had come free from its intended position. The nut was found inside the rocker box cover, and its dimensions matched the damage observed.