On January 2, 1993, a Mooney M20C (registration N6790V) operated by Daniel G. Olivier was involved in an aviation accident near Gorman, CA. Investigators recorded the probable cause as: The inlet fuel fitting had galled or crossthreaded threads, producing metal shavings that bypassed the fuel screen and entered the float valve, causing it to become inoperative and flood the engine, resulting in a total loss of engine power. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise at 9,500 feet, the engine lost all power. The pilot performed a forced landing on a road; a crosswind caused the right wing to contact fence posts, spinning the airplane into an embankment. Investigation found galling of the carburetor inlet fuel fitting allowed metal shavings to disable the float valve, flooding the engine.
Occurrence
The airplane was in cruise flight at approximately 9,500 feet mean sea level when the engine experienced a total loss of power. The pilot entered a power-off forced landing and performed emergency procedures in an attempt to restart the engine, but was unable to do so. The pilot landed the airplane on a two-lane road adjacent to an interstate highway. During the landing, the pilot encountered an unfavorable left crosswind, which caused the airplane to drift to the right side of the road. During the landing roll, the airplane's right wing contacted metal fence posts, spinning the airplane into an embankment.
Examination
During an FAA-supervised engine run, fuel was noted leaking from the carburetor. An examination of the carburetor revealed that the inlet fuel fitting had galling or cross-threaded threads. Metal shavings from the threads bypassed the fuel screen and traveled directly into the fuel float valve without going through the filter screen. This caused the float valve to become inoperative, which resulted in flooding the engine with fuel and causing a total loss of engine power. At the time of the accident, the airplane's engine had a total time of 7 hours since overhaul.
Probable cause
The inlet fuel fitting had galled or crossthreaded threads, producing metal shavings that bypassed the fuel screen and entered the float valve, causing it to become inoperative and flood the engine, resulting in a total loss of engine power.