Accident Sequence
On 16 April 1992, the SA 315B Lama helicopter, registration HB-XFE, departed San Vittore at 0815 local time with a pilot and a mechanic. After a ten-minute flight, it landed at Buzza di Biasca to pick up two passengers and approximately 800 kg of cargo for delivery to a hut at Alpe di Cava. The pilot decided to split the load into two rotations. The first load, in a net, comprised two backpacks, two gas bottles, and several gasoline cans. The two passengers boarded, while the mechanic attached the net to the external hook. At takeoff, the pilot noted the load weighed 500 kg.
The helicopter flew via Val Potirone without incident. Upon arrival at Alpe di Cava, the passengers pointed to a hut near which a red crawler was parked. The pilot intended to place the load beside the crawler. While hovering next to the vehicle, he climbed and moved right with a backward translation, approaching the hut. Suddenly, the helicopter descended. To avoid striking the hut roof, the pilot pulled collective pitch. The helicopter then began an uncontrolled yaw rotation to the left. The pilot jettisoned the load but lost control after several turns. The aircraft crashed on a snowy meadow on the opposite side of the hut at 0850. The occupants exited on their own. A Rega helicopter evacuated the two passengers, who had sustained slight head injuries.
Investigation Findings
The investigation found that the pilot held a valid professional helicopter pilot license and was not suffering from any health issues. He was not wearing a helmet. The helicopter was certified for commercial VFR day operations and had no technical defects. Fuel quantity (200 liters) and mass and center of gravity were within limits. The external load net was attached with a 9-meter strap; the net itself was approximately 11 meters in height. The helicopter had a bubble door, and the pilot relied on external mirrors to monitor the load. An ELT was installed but its activation could not be confirmed. There had been no discussion between the pilot and passengers regarding the precise drop location. The hut roof sustained slight damage from net contact, but no tail rotor impact marks were found. Deformations of the tail and cabin indicated the helicopter was turning left at impact.
Weather at the accident site was: wind from north at about 10 knots with gusts to 20 knots, visibility greater than 10 km, temperature 3°C, dew point 8°C, pressure 1021 hPa QNH, sun azimuth 99°, elevation 22°. The pilot later reported being disturbed by diffuse light and sudden wind variations when the Rega helicopter arrived.
Analysis
The pilot had approached into wind without turbulence, using the red crawler as a visual reference. Fresh snow created diffuse light. Believing the passengers wanted the cargo near the hut door, he shifted the helicopter right and backward while watching the load via mirrors, losing sight of the initial reference. When he felt the helicopter descend, he pulled collective, which induced a left yaw due to power increase. Without visual references, he could not correct and lost control. He jettisoned the load correctly. The helicopter made several revolutions before striking the ground, first with the tail, then coming to rest on its right side. The pilot, though not wearing a helmet, was not injured. The passengers sustained facial cuts.
Cause
The accident was attributed to loss of ground reference, loss of control, and insufficient pilot experience in aerial work.