What happened
On February 27, 2014, a Jodel D1s40C Mousquetaire, registration F-BJQT, was conducting a mountain flight training mission at the Grande Motte glacier. The flight, involving an instructor and a student, was intended to prepare for mountain ski qualifications. Upon arrival, the crew observed several tracks on the snow-covered surface, including two landing tracks and one takeoff track. The crew initially landed on the easternmost landing track, but due to a late application of power, they were unable to reach the top of the slope and stopped approximately 20 meters short of the upper section.
To complete the mission, the instructor decided to disembark the student and perform a solo takeoff to reach the top of the glacier and retrieve the student. During the maneuver, the instructor inadvertently aligned the aircraft with a nearby landing track rather than the intended takeoff track. As the aircraft accelerated at maximum power, the pilot felt a loss of momentum. Because the aircraft was on an incline, the pilot determined that stopping was not possible without damage and continued the takeoff roll. The aircraft subsequently struck rocks and overturned.
The investigation
The investigation examined the environmental conditions and the aircraft's performance. At the time of the accident, the weather was clear with light winds, and the surface was covered in 10 to 15 centimeters of fresh, powdery snow. While a previous pilot had operated on the surface without issues, the student noted that the snow depth in certain areas reached 30 to 40 centimeters.
Analysis of amateur video footage showed that the engine maintained a stable RPM of approximately 2,430 throughout the takeoff roll. However, the aircraft's maximum speed reached only about 80 km/h, which was below the required takeoff speed of 100 km/h. The investigation also noted that the instructor, an experienced mountain flight instructor, realized too late that the aircraft was not aligned with the correct track.
Findings
- The aircraft attempted to take off using a landing track that was too short to allow for sufficient acceleration.
- The pilot's late detection of the incorrect alignment prevented a safe abort of the takeoff.
- The aircraft encountered uncompacted, fresh snow at the end of the landing track, which prevented the aircraft from reaching the necessary takeoff velocity.
- On sloped, snowy surfaces, once a takeoff roll has commenced, it is generally impossible to safely interrupt the maneuver due to the gradient.