What happened
On August 13, 2017, a DG-800 B glider, registration HB-2370, was conducting a private VFR flight originating from Montricher. After an initial self-launch and period of gliding, the pilot was maneuvering near the slopes of the Mont Bifé region. During the final stages of the flight, the aircraft was flying at a relatively low altitude, performing turns away from and toward the terrain. At approximately 12:42 PM, the aircraft entered a right-hand turn toward a ridgeline. Shortly after flying over the crest, the aircraft suffered a loss of control and struck a steep alpine meadow known as Bifé-Dessus, near Villarvolard. The impact was severe, destroying the aircraft and resulting in one fatality.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) analyzed flight data from the aircraft's GPS logger, the Open Glider Network (OGN), and witness statements. The investigation examined the aircraft's technical condition, the pilot's experience, and the meteorological environment. Investigators found that the aircraft was within its weight and balance limits, with the center of gravity positioned at the rearmost allowable limit. The investigation also reviewed the pilot's flight history, noting significant experience with this specific model. While the weather was sunny with some turbulence, investigators determined that meteorological conditions did not directly cause the accident.
Findings
- The aircraft turned toward a ridgeline, and following the overflight of the crest, the pilot lost control.
- The aircraft was flying at speeds significantly below the recommended minimums for the terrain; during the final 90 seconds, the airspeed fluctuated between 75 km/h and 100 km/h, whereas the manufacturer recommends higher speeds for safe maneuvering in such conditions.
- The pilot was flying with a rearward center of gravity, which can make the aircraft more sensitive to pitch and harder to maintain optimal speed during turns.
- The loss of control occurred after the aircraft turned back toward the slope, though the exact reason for the turn toward the ridge or the specific mechanism of the loss of control could not be definitively determined.
- There were no signs of pre-existing mechanical failures or bird strikes.