What happened
On 18 February 2022, a student-pilot was conducting a solo instructional flight in a Guimbal Cabri G2, registration F-HGRE, at Grenoble-Isère airport. After completing a cross-country flight, the pilot began hover taxiing toward parking point A7. During this phase, the helicopter encountered strengthening winds and turbulence.
As the aircraft moved through the parking area, it began to drift to the left. The pilot attempted to correct the movement with right rudder input, but the aircraft's yaw rate to the left increased significantly. In an attempt to gain altitude and avoid the ground, the pilot pulled on the collective pitch lever. This action, combined with the existing wind conditions, caused the rotor speed to drop and the leftward rotation to accelerate. The helicopter completed approximately six full rotations before striking a lighting pylon at a height of roughly five meters. The impact caused the tail boom to break, and the aircraft fell vertically to the ground. The student-pilot sustained injuries, and the helicopter was destroyed.
The investigation
The BEA examined flight data from the aircraft's MultiFunction Display (MFD), radio communications, and video surveillance. The investigation focused on the aerodynamic characteristics of the Fenestron tail rotor and the adequacy of pilot training. Investigators reviewed manufacturer Service Letters regarding yaw control and evaluated the training curriculum at the FHATO Flight Training Center. Meteorological data confirmed that while the morning forecast was calm, significant wind gusts of over 20 knots were present at the time of the accident due to terrain-induced turbulence.
Findings
- The primary cause of the accident was a loss of yaw control during hover taxiing, triggered by a crosswind from the right.
- The pilot's attempt to increase altitude by pulling the collective pitch lever increased engine torque and contributed to a drop in rotor speed, which reduced tail rotor effectiveness.
- The student-pilot's rudder input was insufficient to counteract the increasing yaw rate.
- The training program at the ATO did not sufficiently address the specific aerodynamic challenges of the Fenestron tail rotor, particularly regarding the high level of pedal input required during sudden yaw departures.
- There was a lack of awareness regarding the specific instructor training modules offered by the manufacturer.