What happened
On February 9, 2003, an Eurocopter AS 350 B3, registration F-GMBH, was conducting a mountain rescue mission near Samoëns, France. The flight, operated by Mont Blanc Hélicoptères, was tasked with transporting a ski patroller to the Tête du Pré des Saix summit.
During the landing sequence at an altitude of 2,118 meters, the pilot attempted to land on a strip of snow that had been leveled by a grooming machine. As the aircraft approached the landing zone, it experienced a sudden yaw to the left. The pilot attempted to correct the movement using the pedals and collective pitch, but the aircraft entered an accelerating rotation. Unable to maintain control, the pilot lowered the collective to force the aircraft onto the ground, causing the helicopter to tip onto its right side. While there were no fatalities among the crew or the passenger, the aircraft sustained heavy damage.
The investigation
The investigation focused on the structural failure of the tail rotor. Investigators recovered a tail rotor blade that had been torn from its attachment point and found approximately 100 meters downslope from the wreckage. Laboratory analysis of the blade revealed a static rupture of the fiberglass spar, characterized by compression on the upper surface and tension on the lower surface. This type of damage is consistent with an impact against a compact but non-hard object.
Witnesses on the ground reported seeing a small cloud of snow and a dark object flying from the rear of the helicopter just before the loss of control. The investigation also examined the landing site, noting the presence of snow mounds left by the grooming equipment and the lack of any signage or barriers to demarcate the landing area.
Findings
- The primary cause of the accident was the tail rotor blade striking a mound of compact snow left by the grooming machine.
- The impact caused the blade to separate, leading to an imbalance that disconnected the tail transmission and resulted in a total loss of directional control.
- Contributing factors included insufficient preparation of the landing zone by the grooming service and the presence of bystanders near the landing path.
- Reduced depth perception due to "whiteout" conditions and the pilot's failure to use the specialized yellow visors on his helmet hindered the assessment of obstacles.
Safety action
To prevent similar occurrences, the BEA recommended that the DGAC ensure that agreements between helicopter operators and local municipalities include specific requirements for the signaling of helipads and the precise maintenance of groomed landing surfaces.