What happened
On the evening of September 22, 2009, a Schleicher ASK 13 glider, registered F-CHHI, departed from the La Motte du Caire airfield carrying a pilot and one passenger. The flight was intended for ridge soaring. At approximately 18:37, the aircraft struck the ground on the Montagne de la Blanche, located roughly 36 kilometers east of the departure point.
At the time of the accident, local weather conditions were reported as having a 10-knot wind from 030°, visibility exceeding 10 km, and clear skies with a temperature of 25 °C. While the exact final flight path could not be reconstructed, data from the onboard FLARM system allowed investigators to determine the precise time of the impact and revealed that the aircraft had been experiencing a progressive loss of altitude during the four minutes leading up to the collision.
The investigation
The investigation focused on the flight dynamics and the environmental conditions present during the flight. Investigators utilized data from the aircraft's FLARM calculator to establish the timeline of the descent. The investigation also considered the experience levels of the occupants; the passenger, a flight instructor from a Dutch gliding club, had limited experience in mountain flying, while the pilot in the rear seat was a highly experienced glider pilot with 787 flight hours and 15 years of experience flying in the region.
Findings
Analysis of the flight data indicated a steady decline in altitude prior to the impact. Furthermore, feedback from other glider pilots operating in the area on the same day suggested that the meteorological conditions were not ideal for ridge soaring. The investigation concluded that the primary cause of the accident was the decision to perform ridge soaring on the leeward side of a ridge during weather conditions that were unfavorable for such maneuvers.