What happened
On August 25, 2007, a pilot operating a Tecnam P 96 Golf 100 ultralight, registration 74-PT, departed the Saint-Roch Mayères altisurface for a flight to Annecy. The flight was part of a round trip, and the pilot was accompanied by a friend flying a Jodel D 119.
Shortly after takeoff, the pilot reported engine difficulties over the radio and declared an intention to divert to Megève. During the subsequent maneuvers, the engine ceased operation while the aircraft was on final approach. The aircraft drifted off the flight path, turning right toward the valley, and collided with trees approximately 200 meters from the runway axis. The aircraft became lodged in the treetops. Following the impact, the pilot opened the canopy and fell approximately 15 meters to the ground, resulting in one fatality. The aircraft was destroyed.
The investigation
Investigators examined the wreckage and the engine components. The engine, a Rotax 912 S, was tested on a test bench and functioned normally; no mechanical anomalies or fuel system defects were found in the engine or its accessories. The investigation noted that the fuel taps were in the open position, while the electric pump and electrical master switch were both in the OFF position.
Because the aircraft was parked perpendicularly to the slope of the altisurface during the stopover, investigators studied the potential for fuel migration. Ground experiments demonstrated that when the aircraft is parked at such an angle with both fuel taps open, approximately ten liters of fuel can transfer from the higher tank to the lower tank within ten minutes. Such a transfer can lead to engine fluctuations or pressure drops if a tap remains open while one tank is nearly empty.
Findings
- The engine failure occurred during the return to the altisurface after the pilot attempted to manage the initial engine issues.
- The pilot likely attempted to seek an alternative landing site after realizing the runway could not be reached following the engine stoppage.
- The exact cause of the engine failure could not be determined.
- Potential fuel imbalances caused by fuel migration between tanks during the stopover were identified as a factor that could lead to fuel pressure variations, though no definitive cause was established.