What happened
On July 11, 2011, a Robinson R44 helicopter, registration EI-MUL, was performing a flight from Chambéry to the Méribel altiport with a pilot and one passenger. During the flight, the pilot expressed a desire to land in a confined area. The passenger, an experienced aviator, suggested a clearing near the Refuge de la Traie. Upon arrival, the passenger noted that the original intended area was unsuitable due to tall grass and suggested an alternative path along a cleared track upstream from the refuge.
As the pilot approached the site, the aircraft followed a descent path along the terrain, flying at a very low altitude of approximately one meter over a bend in the road. Witnesses observed the helicopter approaching at a very low airspeed before it suddenly sank. During this descent, the left skid made contact with a rock, causing the helicopter to tilt to the right, strike the ground, and catch fire. Both occupants sustained two injuries, and the aircraft was destroyed.
The investigation
The investigation focused on the aircraft's performance capabilities relative to the environmental conditions at the time of the accident. The helicopter was equipped with a Lycoming O-540 carbureted engine, which provides less power than the fuel-injected version. At the time of the accident, the temperature was 19°C (ISA + 14°C) and the aircraft weight was approximately 1,010 kg.
Investigators determined that while the aircraft was capable of hovering in ground effect (IGE) up to approximately 7,100 ft, it could not maintain a hover out of ground effect (OGE) above 4,100 ft. The investigation also examined the pilot's experience and the influence of the passenger, who held extensive flight qualifications and significant helicopter experience.
Findings
- The pilot was performing an approach at a low airspeed that required high power settings.
- As the aircraft followed the terrain, it initially benefited from ground effect while flying low over the road bend, but lost ground effect as the terrain elevation increased during the approach.
- This loss of ground effect likely caused the sudden sink and subsequent instability.
- Gusty winds from the north-northwest (8 knots with 20-knot gusts) may have further destabilized the rotor lift.
- The presence of a highly experienced passenger may have inadvertently contributed to a lapse in the pilot's judgment.
- The primary cause was the pilot's failure to sufficiently account for the aircraft's performance limitations during a high-altitude approach in high temperatures.