What happened
On June 28, 2008, at approximately 04:15 UTC, a Rutan Long-Ez, registration F-PPOT, departed from the Montélimar Ancône airfield for a private flight to Angoulême. The pilot was the sole occupant of the aircraft. During the flight, the engine suffered a failure, leading to a loss of power. The aircraft's wreckage was discovered later that morning on the southern slope of Mont Tanargue at an altitude of 1,380 meters. The impact occurred with the aircraft flying in a direction opposite to its intended route, suggesting the pilot was attempting an emergency landing in the terrain below.
The investigation
The investigation focused on the mechanical state of the engine and the pilot's medical condition. Examination of the engine revealed that the upper spark plugs in all four cylinders were loose and could be removed by hand. Specifically, the upper spark plug in cylinder number 3 was leaking, and the lower plug in the same cylinder was obstructed. Further inspection of the carburetor identified excessive play in the float shaft, which allowed the float to jam the needle valve in the open position, resulting in an over-rich fuel mixture.
Analysis of the wreckage showed the aircraft struck a rock outcrop on the left side of the fuselage, causing the plane to slide and eventually flip. The investigation also noted that the pilot performed his own aircraft maintenance. Additionally, medical examinations of the pilot revealed a pre-existing pathology that predisposed him to acute cardiac events or fainting.
Findings
- The engine failure was caused by an excessive fuel mixture resulting from a faulty carburetor.
- The maintenance of the aircraft was found to be insufficient, as evidenced by the loose spark plugs and the carburetor defect.
- The pilot's attempt at an emergency landing failed, potentially due to insufficient altitude to clear the rugged terrain or a sudden medical incapacity triggered by the stress of the engine failure.
- The engine was not delivering power at the moment of impact, as indicated by soot patterns on the propeller blades.