2015 Guimbal Cabri G2 accident in France (F-HOLA)

Flight and Accident Sequence On 12 March 2015, a Guimbal Cabri G2 helicopter, registration F-HOLA, powered by a Lycoming O-360-J2A engine, departed from Grenoble Le Versoud aerodrome at 10:00 local time for maneuvering exercises. The flight was conducted by an instructor and a student. After completing the exercises, they proceeded to a pass at an altitude of 5,400 ft on the Matheysine plateau. The instructor took control to assess the area, noting light winds of uncertain direction. During a hover in ground effect, one skid contacted the snow. After taking off and turning around, the helicopter approached from the opposite direction. As the instructor increased collective pitch to leave the hover, the aircraft suddenly began rotating to the left in yaw. The instructor applied full right rudder, increased collective pitch, and increased power to gain altitude. The helicopter completed five to six rotations on its yaw axis. The instructor then lowered the collective pitch, reduced power, and made a hard landing in the snow. The engine was shut down. The helicopter was heavily damaged. ## Investigation Findings The accident site was a snow-covered pass at approximately 5,400 ft, with a layer of ice beneath the snow. The airframe was rotated approximately 15 degrees to the left, and the tail boom was partially broken at the anti-torque rotor junction. The rear transmission shaft was broken due to sudden overload from the hard landing. The flight plan indicated light winds from the west up to FL050 and 15 kt from the north-northeast at FL100, with moderate turbulence from FL050. A temperature inversion at 5,500 ft was also noted as a turbulence generator. The instructor held a CPL(H) and FI(H) qualification, with 3,800 total flight hours, including 68 hours on type. The student had 14 hours of flight time, all in dual command on the same helicopter. The instructor estimated the required power for a hover in ground effect at 92%. The helicopter was within the manufacturer's mass and center of gravity limits. According to the flight manual, the hover ceiling was 5,400 ft out of ground effect and 6,600 ft in ground effect. At 5,400 ft and +5°C, the required power for a hover in ground effect was 90 to 95% without wind. Hovering into a tailwind requires more power due to rotor disk tilt. ## Probable Cause The loss of yaw control occurred during the departure from a hover in a tailwind in turbulent aerology, while the helicopter was near its performance limits. The instructor's actions to gain altitude increased the main rotor torque, exacerbating the left yaw rotation. The subsequent reduction in collective pitch and power helped reduce the yaw rotation before impact. The instructor's actions did not stop the rotation and may have contributed to maintaining the yaw movement.