What happened
On 14 March 2022, a Schleicher ASH25 glider, registered F-CLMR, was conducting an instructional flight near Volonne, France. The flight, operated by Centre Savoyard de Vol à Voile Alpin, began with a towed takeoff from the Château-Arnoux - Saint-Auban aerodrome. Initially, the pilot under instruction utilized updrafts near the Durance river dam, reaching an altitude of 1,470 m.
As the aircraft moved north toward a developing cumulus cloud, it crossed onto the lee side of the Ruth mountain ridge. In this area, the glider encountered strong downdrafts. The instructor took control of the aircraft to navigate the ridge line at approximately 1,200 m. As the terrain elevation increased, the aircraft's altitude relative to the ground decreased.
Seeking to find thermal lift, the instructor initiated a right turn into a valley. During this maneuver, the glider's vertical speed turned negative. The aircraft struck the branches of an oak tree before colliding with the ground 30 meters further on. The two occupants, an instructor and a student, were uninjured and were rescued by helicopter approximately 45 minutes after the impact.
The investigation
The BEA investigation relied on statements from the instructor and data extracted from the aircraft's FLARM unit. The investigation examined the instructor's flight experience, the meteorological conditions at the time of the accident, and the decision-making process regarding the flight path. Investigators also reviewed the weather forecast, which had indicated an unstable air mass and a risk of rain, though the actual conditions at the time of the accident were sunny with moderate turbulence and a south-easterly wind of 10 to 15 knots.
Findings
Several factors contributed to the accident, primarily centered on the insufficient altitude margin maintained relative to the terrain. The investigation established that:
- The flight path followed the terrain too closely, leaving inadequate clearance above the ridge line.
- The instructor's decision-making was influenced by an erroneous interpretation of the local air conditions and an overconfidence in the availability of lift.
- The instructor's choice of path may have been affected by the recent resumption of flying after a period of inactivity.
- A late decision to divert into the valley to avoid abandoning the flight contributed to the loss of altitude during the turn.