What happened
On 9 February 2021, a Bell 206B helicopter, registration F-HUBA, was conducting a private flight over the Les Trois Vallées ski area in the French Alps. The flight departed from Courchevel mountain airfield with the pilot and four passengers, intended to be a short 20-minute sightseeing tour.
As the aircraft traveled southeast toward the Mount Charvet ridge, it flew at low speed and low altitude. While traversing the ridge line, the helicopter entered a slight descent. During this maneuver, the tail rotor blades struck the snow-covered terrain of a mountain spur. The impact caused the tail rotor drive shaft to rupture due to sudden torsional stress, leading to a total loss of yaw control. The helicopter spun, the tail boom detached, and the aircraft fell and slid down the steep western slope of the ridge, breaking into several pieces upon impact.
The investigation
The investigation utilized data from the IntelliStart flight recorder, radio communications, and video footage recovered from passengers' mobile phones. Analysis of the engine parameters and spectral analysis of the video recordings confirmed that the engine was delivering power up to the moment of impact and showed no signs of mechanical failure or propulsion assembly deterioration prior to the collision.
Physical examination of the wreckage revealed that the tail rotor blades had interacted with the snow, creating a resistive overtorque that caused the drive shaft to fail. The investigation also noted that the aircraft was within its maximum permissible weight limits at the time of takeoff.