Cat. 3 investigation report: report concerning an occurrence with limited consequences, based on one or more statements not independently validated by the BEA.
This is a courtesy translation by the BEA of the Final Report on the Safety Investigation published in May 2022. As accurate as the translation may be, the original text in French is the work of reference.
Note: The following information is principally based on statements made by the pilot. This information has not been independently validated by the BEA.
1 - HISTORY OF THE FLIGHT
While finishing a mission at La Mure, the pilot was contacted by the Grenoble SAMU (emergency medical services) to intervene at Les Deux Alpes and take charge of a person requiring emergency medical care who would then have to be taken to Grenoble hospital. He checked the compatibility of the available meteorological information and the helicopter's performance and then took off, at around 13:30, from La Mure Helicopter Landing Surface (HLS) to a HLS in Les Deux Alpes. He made two complete circuits around the HLS while waiting for another helicopter to take off. He then performed a standard approach with a descent rate of 500 ft/min, which he checked at the beginning of the approach. When the height was no longer enough to reject the landing, at about 20 m above the HLS, he felt the structure vibrate and the helicopter sink. He tried to counter the sinking by pulling on the collective pitch control but was unable to absorb the rate of descent sufficiently. The helicopter hit the ground hard and then returned to hover a few centimetres above the ground due to the power applied. The pilot quickly controlled the vertical descent of the helicopter and landed normally. On the first impact, the rear cross tube of the skids bent by about ten centimetres and the tail boom bumper collided with the ground.
2 - ADDITIONAL INFORMATION
The pilot held a CPL(H) commercial helicopter pilot licence issued in 2013. At the time of the accident, he had logged approximately 4,850 flight hours. Since 2019, he had been flying exclusively on the EC135 with 440 hours of flight experience on the day of the accident, including 37 hours in the last three months. He had been an EMS pilot since 2019 and employed by SAF Hélicoptères since the autumn of 2020.
Les Deux Alpes ski resort has two HLS, "DZ 1" and "DZ 2". Work had been in progress at “DZ 1", usually used for the emergency medical service missions, since 24 March 2022. The pilot indicated that this was the first time he used "DZ 2". Before take-off, he consulted the "DZ 2" sheet, written by the operator, which recommends using only the approach path oriented 073°, due to the houses and the terrain around the HLS.
The pilot stated that on initially approaching the HLS he felt a light, laminar, southerly wind with no turbulence. He added that the position of the windsock, located on a flat section of the HLS, was variable and indicated an unsettled wind. On the ground, after the accident, he periodically felt strong gusts from an updraft along the cliff at the edge of the HLS.
The pilot stated that on final he did not perceive an increase in the rate of descent prior to the sudden sink.
Although he had not felt any “softness” in the controls, the pilot thought that the helicopter probably entered its vortex during the final approach, due to the combination of the tailwind and the updraft along the cliff. He added that he had chosen to comply with the approach method recommended by the flight manual, but that an approach with a smaller slope angle, and a path along the terrain to allow the landing to be rejected as late as possible, would have been more appropriate in the wind conditions encountered.
 Aerodynamic stall of the main rotor blades, likely to occur at low airspeed and a descent rate close to the "induced speed" of the main rotor (typically 700 ft/mn to 2500 ft/mn). When the helicopter is descending and the main rotor is not horizontal, the speed experienced by the main rotor is higher. This is referred to as a "dynamic" vortex, which can occur at lower rates of descent.
Downwind approaches, steep approaches and poor vertical hold of hover are conducive to the appearance of a vortex. A high collective pitch that increases the rotor blade angles also facilitates the occurrence of the vortex ring.