What happened
On June 12, 2021, an Eurocopter EC 120B, registration HB-ZCA, was performing a private recreational flight. The aircraft departed Lausanne-La Blécherette (LSGL) with five occupants, including two children, traveling toward Montreux and the Dents du Midi.
During the return leg of the flight, the pilot approached runway 18. Upon completing the landing, the pilot initiated a left turn out of ground effect to maneuver toward the hangar tarmac. During this turn, the aircraft entered a series of left-hand rotations around the yaw axis. The helicopter eventually made a hard landing on the grass at the edge of the runway. While the occupants escaped without injury, the aircraft sustained grave damage to the landing gear.
The investigation
Investigators reconstructed the event using statements from the pilot and passenger, as well as airport surveillance footage. The footage confirmed a stabilized approach on runway 1 and the start of a left turn at low translational speed. The investigation focused on the transition from a 90-degree course change to the uncontrolled rotation around the yaw axis.
Findings
- The primary cause of the incident was a loss of control in yaw near the ground.
- The pilot failed to apply appropriate pedal inputs to counteract the torque changes associated with the power demand during the turn.
- The investigation noted that the pilot's decision to reduce power by lowering the collective prevented more severe damage.
- It was determined that applying significant right pedal input would have stopped the rotation and prevented the landing gear damage.
- The manufacturer's documentation (IN 3539-I-003) specifies that aircraft equipped with a Fenestron tail rotor require larger pedal amplitudes during the transition from cruise flight to a hover compared to conventional tail rotors.