What happened
On August 12, 2015, an Arcus M self-launching glider, registration HB-203, crashed into the western slope of the Petit Col Ferret in the Courmayeur region of Italy. The aircraft had departed from Bex Airport in Switzerland for a recreational VFR flight. During the flight, the glider performed a series of turns while traversing the mountainous terrain. In the final moments of the flight, the aircraft entered a left-hand turn and struck the steep, rocky slope at an altitude of approximately 2,446 meters. The impact caused the total destruction of the aircraft, and both occupants sustained fatal injuries.
The investigation
The ANSV investigation examined the flight data from the onboard LX9000 system, wreckage analysis, and eyewitness accounts. Data logs revealed that the aircraft had been flying for approximately two hours before the accident. In the final minutes, the glider transitioned from a thermal over the Combe de l’A valley into a series of maneuvers. The investigation noted that the aircraft's ground speed increased from 130 km/h to 163 km/h just before impact, accompanied by a loss of altitude.
Investigators also examined the mechanical condition of the wreckage, specifically looking at the airbrake control mechanisms. While a missing pivot pin was discovered on the left airbrake crankshaft, the analysis concluded this was a result of the extreme forces during the impact rather than a pre-existing defect. Furthermore, the investigation considered the solar position, noting that the sun was at a high elevation and positioned almost directly in front of the aircraft, which could have caused glare or obscured terrain features.
Findings
- The primary cause of the accident was the impact of the glider against the western slope of the Petit Col Ferret during a left-hand turn, where the separation from the terrain was insufficient to clear the obstacle.
- A significant contributing factor may have been an inadequate assessment of terrain clearance by the pilot, potentially exacerbated by solar glare or shadows cast by the mountains.
- The presence of mountain rotors (turbulent air) caused by wind interacting with the rugged topography may have prevented the aircraft from gaining the necessary altitude to clear the slope.
- Eyewitnesses reported seeing the wings of the glider moving erratically just before impact, which is consistent with the presence of such aerodynamic disturbances.