Incident Summary
A pilot reported losing power in both engines approximately one hour after departing with a full fuel load. The pilot performed an emergency landing in a field and exited the airplane. Following the landing, the pilot observed that the fuel cap was off and hanging by its chain.
Investigation Findings
Examination of the airplane revealed no fuel in the fuel system. There was no evidence of fuel splatter on the wing, fuselage, or tail surfaces. The wing skin around the fuel fill port and the chain attachment point showed no scratches or dents. The fuel cap chain assembly was of a type designed to break free at 20 knots airspeed when left unsecured. The airplane was equipped with a non-siphoning fuel fill port.
Fuel System Details
The pilot reported no mechanical malfunctions, and investigators found no defects with the fuel cap chain. The investigation documented the absence of fuel and the unsecured fuel cap, but no explicit cause for the fuel loss was stated in the available records. The design characteristics of the fuel cap assembly suggest that an unsecured cap could separate in flight, potentially leading to fuel loss, though the source material does not provide a definitive conclusion.