What happened
On July 9, 2020, a Glasflügel 304 CZ glider, registration D-5304, was performing a local flight departing from the Barcelonnette - Saint-Pons aerodrome in the Alpes-de-Haute-Provence region. After releasing from a tow at approximately 1,900 meters, the pilot began thermalling north of the aerodrome.
During the flight, the pilot observed another glider climbing more effectively near the Parpaillon massif. Seeking better lift, the pilot maneuvered toward the other aircraft, flying toward the mountain terrain. Upon realizing the aircraft was becoming too low, the pilot attempted a left-hand turn to retreat from the slope. During this maneuver, the glider entered a thalweg and was struck by a strong downdut, causing a rapid loss of altitude. The aircraft subsequently collided with the treetops, resulting in the destruction of the glider. The pilot was able to exit the cabin and successfully activated a personal locator beacon (PLB).
The investigation
The investigation relied on the pilot's statement, data from the aircraft's FLARM system, and OGN tracking data. Investigators examined the meteorological conditions, which included a west-south-westerly valley breeze of 8 to 20 knots and moderate turbulence. The investigation also reviewed the pilot's flight experience and the specific terrain features, such as the spurs and thalwegs present in the area, which can create complex aerological phenomena.
Findings
Several factors contributed to the accident:
- The pilot's decision to fly toward the mountain face and the late decision to turn around, which necessitated a much tighter turn than intended.
- A loss of situational awareness regarding altitude due to the pilot's focus on following the other glider.
- The presence of a local aerological phenomenon, specifically a strong downdraft associated with the terrain's spurs and thalweg, which caused the sudden loss of altitude during the turn.