What happened
On 2/26/2020, an Aerospatiale AS350 B1 helicopter, registration F-GNLM, was performing a private cross-country flight from Aix-Les-Milles to Toussus-le-Noble, with a scheduled stop at Clermont-Ferrand airport. After refueling and embarking five passengers, the pilot initiated the takeoff sequence.
As the aircraft entered a hover a few meters above the ground, it began to rotate rapidly to the left around its yaw axis. The pilot attempted to counter the rotation by applying the right pedal, but the rotation continued to accelerate, causing the helicopter to bank and roll to the left. In an attempt to gain altitude and move away from the ground, the pilot increased the collective pitch, which inadvertently increased engine torque and further exacerbated the yawing motion. Realizing control could not be regained, the pilot lowered the collective to force the aircraft back to the ground. The helicopter struck the surface with significant force, bouncing before coming to a stop. There were no fatalities, though the helicopter sustained damage.
The investigation
The BEA examined the aircraft's mechanical systems, including the flight control linkages, servocontrols, yaw trim, and the connection between the engine and the tail rotor. No mechanical anomalies or failures were detected in the engine or the tail rotor drive system. Data from the onboard Helisafe computer confirmed the engine was delivering power as expected at the time of the accident.
The investigation also reviewed the pilot's experience, noting a PPL(H) with approximately 470 total flight hours. The aircraft's weight was found to be approximately 2,160 kg, which was near, but within, the maximum takeoff weight of 2,200 kg. Investigators also analyzed aerodrome surveillance footage, which showed a light westerly wind with potential gusts, and reviewed the pilot's statement regarding the presence of dual controls and the position of the front passenger's feet.