What happened
On September 16, 2013, a Robinson R44 helicopter, registration F-GXRF, was conducting a navigation flight from Château de Pennautier to the Font-Romeu helisurface. The flight was part of a group, as three other helicopters were performing the same route.
During the approach, the pilot was flying at a low speed along a north-east axis, attempting to locate a landing area near the other stationary aircraft. When the helicopter was approximately two meters above the ground, a "LOW RPM" alarm activated. This was immediately followed by a hard impact with the ground, causing the aircraft to tip onto its right side. The aircraft sustained heavy damage.
The investigation
The investigation examined the aircraft's configuration and the pilot's actions regarding the engine governor. The helicopter was equipped with a conventional collective pitch control, including a twist-grip power control. The governor system is designed to automatically maintain the engine speed within normal operating limits when switched to the "ON" position.
Investigators reviewed the aircraft's weight and performance limits. At the time of the accident, the estimated mass was 968 kg. While this was within the manufacturer's defined limits, the investigation noted that the maximum allowable mass for a hover in ground effect (HES) under the day's conditions was approximately 970 kg. The investigation could not confirm whether the pilot had calculated the specific mass and performance limits prior to departure.
Findings
Several factors contributed to the loss of rotor speed. The pilot conducted the approach with a tailwind component while operating near the aircraft's performance limits.
Additionally, investigators identified the possibility that the pilot may have inadvertently deactivated the governor. If the governor was turned off, the responsibility for coordinating pitch and power would have shifted to manual control. Without immediate manual adjustment of the power twist-grip by the pilot, the main rotor RPM decreased, triggering the low RPM warning and leading to the hard landing.