What happened
On April 25, 1999, at approximately 15:40, a Schempp Hirth Ventus B glider, registered F-CGLG, was involved in a fatal in-flight breakup near Saix, France. The flight began earlier that day at 11:35 at Fayence. After approximately two hours of flight, the pilot began a return leg toward the departure airfield, heading toward the Rhône Valley.
While flying near the Montagne d'Aujour, located roughly 15 km southwest of Gap, the aircraft entered a cloud. Upon entering the cloud, the glider encountered extremely severe turbulence. This turbulence caused the aircraft to exceed its maximum permissible speed (VNE), reaching approximately 270 km/h against a limit of 250 km/h. In an attempt to manage the descent, the pilot deployed the airbrakes. However, the aircraft began vibrating violently, and the canopy shattered. As the glider maintained a steep nose-down attitude and the pilot lost control, the pilot attempted to bail out. The pilot managed to exit the cockpit after a descent of 4,300 feet, successfully deploying a parachute.
The investigation
The investigation focused on the sequence of events leading to the structural failure of the aircraft. Investigators analyzed the distribution of the wreckage, which confirmed that the Schempp Hirth Ventus B had disintegrated in mid-air prior to impacting the ground. The investigation also reviewed the meteorological conditions at the time, noting visibility was greater than 10 km with scattered clouds at 5,000 feet.
Findings
The investigation established that the primary cause of the accident was the exceedance of the aircraft's flight envelope following an unplanned entry into a cloud. The resulting severe turbulence led to an overspeed condition and subsequent structural failure. The disintegration of the airframe was the direct result of these aerodynamic forces.