What happened
On September 7, 2004, at approximately 9:30 AM, a private Robinson R22 Beta helicopter, registration F-GJBE, was performing a local flight at the Maïdo helisurface in Réunion. After landing at an altitude of 7,000 feet, the pilot remained on the surface for about one minute without shutting down the engine. The pilot then initiated a takeoff from a hover in ground effect, attempting a horizontal departure over the northwest slope of the Maïdo.
As the aircraft climbed out of ground effect, the pilot heard the low rotor RPM alarm and observed the corresponding warning light. In an attempt to recover the rotor speed, the pilot lowered the collective pitch and transitioned into a descent at approximately 60 knots. Despite these efforts, the rotor RPM continued to decay. The helicopter lost altitude and struck the ground several times, eventually sliding approximately 100 meters before coming to rest on its right side. The accident resulted in two injuries (the pilot and one passenger) and the destruction of the aircraft.
The investigation
Investigators analyzed video footage from a witness, which revealed a rapid decline in main rotor speed from 3_90 rpm to 300 rpm within an eight-second period. The investigation focused on the aircraft's performance capabilities at high density altitudes and the pilot's preparation for the flight.
It was established that the pilot was relatively inexperienced, with only 66 total flight hours, 12 of which had occurred in the three months prior to the accident. Although the pilot had completed Robinson safety training, which covers the phenomenon of rotor over-torque, the pilot had not consulted the flight manual prior to the departure. Furthermore, the pilot's instructor had previously advised against landing at altitudes exceeding 5,000 feet due to the pilot's limited experience.
Findings
- The primary cause of the accident was a rotor over-torque event leading to a loss of control.
- At the takeoff altitude of 7,000 feet, the aircraft's mass (538 kg) required more power to maintain a hover out of ground effect than the engine was capable of providing.
- The pilot failed to adequately prepare for the flight or account for the aircraft's performance limitations at high altitude.
- The low altitude at which the departure was attempted prevented an effective recovery maneuver once the power deficit was identified.