Luscombe 8A N28425 accident near Eatonville, Washington

Probable cause

The loss of engine power due to fuel starvation as a result of the pilot's inadequate in-flight fuel management. Contributing to the accident was the airplane's lack of an interconnected fuel vent system.

NTSB analysis

The airplane's engine lost power during cruise flight and the pilot executed a forced landing to a field. During the landing, the main landing gear encountered tall grass and collapsed. Examination of the airplane revealed that the fuselage sustained structural damage. Examination of the engine revealed no evidence of any preimpact mechanical discrepancies that would have prevented normal operation. The airplane was equipped with two 12.5-gallon wing fuel tanks, each of which had its own two-position (on-off) fuel selector valve. The left wing fuel tank was found empty and the right wing fuel tank contained about 4.5 gallons of fuel. During the accident flight, both fuel selector valves were in the 'ON' position, which was the pilot’s normal operating procedure. The airplane does not use an interconnected fuel vent system, but instead uses individual vents in the caps of each tank. With both fuel tank selector valves in the 'ON' position, if one vent is plugged, or partially misaligned, the vent pressure difference will result in unequal fuel flow to the engine and will move fuel from the higher pressure vent/tank to the lower pressure vent/tank. Also, if both fuel tank selector valves are in the 'ON' position, prolonged uncoordinated flight with one wing lower than the other will result in unequal fuel flow to the engine and in fuel flowing from the high to the low wing tank. The loss of engine power was likely due to unequal fuel feed to the engine from the two wing fuel tanks, which resulted in the left tank running dry and interrupting fuel flow to the engine. The reason for the unequal fuel feed was not determined.

Text from the NTSB. Open the NTSB docket for WPR09LA390 for the full record.