What happened
On September 16, 2015, an Airbus Helicopters AS350-B3+, registration F-HCSC, was performing aerial work duties near Tignes, France. The mission involved transporting maintenance personnel to various sites within the mountain resort. After completing several successful shuttle rotations, the pilot attempted to land at the "Dos Rond" site, located at an altitude of 8,260 feet.
During the final approach, the pilot estimated the wind conditions visually and positioned the aircraft to land into the wind. As the helicopter descended to approximately 10 to 15 meters above the ground, the pilot experienced a sudden loss of altitude. Despite an immediate application of collective pitch, the aircraft struck the terrain. The impact caused the helicopter to slide and roll onto its right side, eventually coming to rest against a rock. Of the passengers on board, two passengers were injured after three were ejected from the aircraft during the collision.
The investigation
The BEA examined the wreckage, the flight data from a "Brite Saver" parameter recorder, and the pilot's experience. The investigation confirmed that the aircraft's weight and balance were within manufacturer limits and found no mechanical failures or engine issues prior to the impact. Data from the parameter recorder showed an increasing rate of descent even as engine power was being increased.
Investigators also analyzed the meteorological conditions at the time. While winds at higher altitudes were recorded at 40 knots from the south, surface winds near 8,200 feet were south-southeasterly at 15 knots, with potential gusts reaching 50 knots. The terrain presented a high risk of turbulence and downdrafts due to these strong winds interacting with the mountain slopes.
Regarding survivability, the investigation found that the passengers were not wearing seatbelts. While the aircraft was equipped with three-point harnesses, the practice of not using them had become common during these short-duration flights to save time during embarkation and disembarkation.
Findings
- The primary cause of the accident was the pilot's erroneous estimation of aerodynamic conditions, which led to an approach into a zone heavily affected by downdrafts caused by the terrain.
- The successful completion of previous flight legs under difficult conditions likely contributed to an underestimation of the actual atmospheric instability at the final landing site.
- The severity of the consequences was increased because the passengers were not restrained by seatbelts.