Background
On 29 June 1991, a helicopter AS 350 B2 "Ecureuil", registration HB-XXL, operated by Heli Bernina AG, was tasked with transporting personnel and material to a high-altitude relay station for the Kesch-Stafette event. The pilot held a valid commercial pilot license for helicopters and had accumulated 1,211 total flight hours, with 13 hours in the preceding 90 days.
Flight and Accident
Shortly after 1330 local time (UTC+2), the pilot departed from Samedan Airport. The helicopter picked up approximately 150 kg of internal cargo and five passengers (four officials and one flight helper) east of the Albulapass-Hospiz. The intended landing site was Porta d'Es-cha, located about 40 meters northwest of a ridge at an elevation of approximately 3,100 meters above sea level.
The pilot approached the area from the southwest, crossing the ridge a few hundred meters south of the landing site, then descended toward the Keschhütte. At about 500 meters from the landing point, the pilot initiated a turn in descent to line up for a final approach from the north. During this turn, forward speed was about 60 knots. Approximately 50 meters from the landing zone, the helicopter began to sink rapidly despite increasing main rotor blade pitch. The pilot suspected the helicopter had entered a vortex ring state. He reduced pitch and fully pushed the cyclic forward in an attempt to go around to the east, but the helicopter continued to descend. Just before impact with snow, the pilot pulled full collective until the low rotor rpm warning horn sounded. The helicopter struck the snow about 20 meters left of the intended landing point, at an angle approximately 60 degrees off the approach path. The pilot shut down the engine using the fuel shutoff.
Injuries and Damage
One passenger sustained minor injuries; all other occupants, including the pilot, were uninjured. The helicopter sustained damage including a bent tail boom, broken right front skid, and slight compression of the main structure on the left side.
Findings
The investigation found that the pilot was properly licensed and authorized for the flight. No evidence of pre-existing or in-flight medical issues was found. The helicopter was airworthy and properly maintained, and no technical faults contributed to the accident. Weight and balance were within limits. Weather at the site included north wind around 15 knots with gusts to 30 knots, occasional snow showers, and diffuse light conditions.
The assessment noted that the approach tactic, particularly the final turn with descent and tailwind conditions, led to a high rate of descent that promoted vortex ring conditions. The pilot's corrective actions (reducing pitch and pushing cyclic forward) were appropriate but initiated too late to prevent ground contact.
Cause
The accident was due to an inadequate approach tactic.