What happened
On June 16, 2024, a trainee pilot was conducting her third instructional flight in a Jonkers Sailplanes JS1-C sailplane, registration ZS-GUA, near Courtelary, Switzerland. The flight, which was part of a transition training program to this specific model, began with a tow from Courtelary airfield. After releasing from the tow cable at an altitude of approximately 1,502 meters, the pilot began searching for thermals.
During the flight, the aircraft encountered turbulent wind conditions. At approximately 12:41 UTC, while flying at an altitude of roughly 1,350 meters (about 250 meters above ground level), the aircraft experienced a significant drop in airspeed. This led to a stall and subsequently a spin. Due to the low altitude, the pilot was unable to recover from the spin before the aircraft impacted a wooded area on Mont Crosin. The pilot managed to exit the wreckage on her own, sustaining light injuries.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined flight data from the onboard LX9000 flight computer and the PowerFlarm system, alongside statements from the pilot and the instructor. The investigation reviewed the aircraft's maintenance history, noting it had undergone its annual inspection earlier in 2024. The investigation also analyzed the meteorological conditions at the time of the accident, which included turbulent orographic lift and moderate thermals.
Physical inspection of the wreckage revealed that the aircraft's center of gravity was near the rear limit. The investigation found no evidence of structural failure or mechanical malfunction prior to the accident. The flight instruments remained intact following the impact, and the aircraft's engine, flaps, and landing gear were all in the retracted position.
Findings
- The primary cause of the accident was a loss of control resulting from a stall.
- The aircraft entered a spin that could not be recovered due to the insufficient altitude above the terrain.
- Challenging meteorological conditions, characterized by turbulent winds, contributed to the accident.
- The pilot's limited flight experience, specifically her lack of experience with this particular aircraft type and similar high-performance models, contributed to the occurrence.