What happened
On May 25, 2010, a Schleicher ASK 18 glider, registration F-CERI, was engaged in a local ridge soaring flight near Chambéry Challes-les-Eaux. After taking off via winch launch, the pilot headed toward the Galoppe massif. Seeking to join another glider operating at 2,500 meters, the pilot navigated toward the Corbelet mountain.
Data from the FLAM® flight recorder indicates that after 80 minutes of flight, the aircraft was at 1,800 meters while crossing the valley. As the pilot began maneuvering on the eastern flank of the first cirque, the altitude had dropped to 1,300 meters with a slight constant descent. By the time the aircraft reached the second cirque, the altitude had decreased to 1,100 meters with a descent rate of -5 m/s, placing the aircraft below the 1,300-meter safety altitude established by the gliding flight center for that sector.
Upon entering the second cirque, the pilot encountered heavy turbulence and a sink rate of -4.5 m/s. Realizing the flight could not be sustained, the pilot attempted a turnaround, during which intense turbulence caused the canopy to open unexpectedly. While the pilot focused on closing the canopy, flight control was compromised. After announcing an intention to land in a field and activating the emergency beacon, the pilot attempted an off-airport landing. During the final approach, the glider struck a high-voltage utility pole with the right wing and a tree with the left wing, resulting in the destruction of the aircraft.
The investigation
The investigation focused on the flight path recorded by the FLAM® device and the pilot's decision-making regarding terrain and altitude. Investigators examined the meteorological conditions, which included a 20-knot western wind at 1,500 meters and highly turbulent atmospheric conditions. The investigation also reviewed the safety altitude documentation provided by the gliding flight center, which the pilot had in his possession.
Findings
- The pilot chose to continue flight below the recommended safety altitude in an area characterized by unfavorable aerological conditions.
- Severe turbulence contributed to the loss of altitude and caused the accidental opening of the cockpit canopy.
- The pilot's attention was diverted by the need to secure the canopy during a critical phase of flight.
- The aircraft struck obstacles (a utility pole and a tree) during the forced landing maneuver.