Incident Overview
A pilot reported experiencing an engine vibration approximately 10 minutes after takeoff. He decided to return to Williston to perform a precautionary landing. While approaching the downwind leg for runway 29, the engine seized. Unable to reach the runway, the pilot aimed to land on airport property. He observed hay bales and equipment in his intended landing area and maneuvered to avoid them. During the maneuver, the airplane stalled in a near level attitude and impacted the runway berm.
Engine Examination
Post-incident examination of the engine revealed a fuel system issue: the mixture was running rich at low power settings but lean at high power settings. The fuel pump was delivering 22 psi of fuel pressure, below the specified 34 psi. Inspection of the number four piston showed severe erosion around its perimeter, characteristic of combustion chamber detonation.
Sequence of Events
The pilot initially noticed an engine vibration shortly after departure and opted to return for a precautionary landing. On the downwind leg, the engine seized. The pilot then attempted to land within the airport boundary but had to avoid hay bales and equipment. The avoidance maneuver led to an aerodynamic stall, and the airplane struck the runway berm.
Findings
The fuel system discrepancies and piston damage were documented. No other factors were mentioned in the source material.