What happened
On February 15, 1974, an SA 315 B Lama, registration HB-XDZ, operated by Heliswiss Schweiz. Helikopter AG, was conducting a commercial transport flight in the Turtmanntal region of Switzerland. After performing several cargo transfers near Gampel and Oberems, the pilot attempted to pick up two workers and an aircraft mechanic from a small forest clearing known as Hungerli-Mittelstafel.
The mission had already encountered complications when an attempt to lift a heavy winch failed due to insufficient engine performance, forcing the crew to switch to lighter loads. During the final boarding attempt in a narrow clearing, the pilot performed a hover landing with one ski touching the snow. Because the left skid was too high for the workers to climb in from the left side, the workers moved underneath the aircraft to reach the right side.
As the pilot attempted to descend, one worker jumped onto the right ski and pulled a second worker up onto the skid. This sudden movement shifted the aircraft's center of gravity significantly to the right. Despite the pilot's efforts to compensate using the flight controls, the SA 315 B Lama tilted heavily toward the slope. The main rotor struck the hillside, causing the helicopter to capsize and come to rest on its right side.
The investigation
SUST examined the mechanical condition of the aircraft, the weather conditions, and the experience levels of the personnel involved. The investigation confirmed that the aircraft was in good technical condition and that the takeoff weight was within legal limits. However, the presence of the two men on the skid shifted the center of gravity to approximately 10 cm right of the centerline, exceeding the allowable lateral limit.
The weather was reported as stable with light winds and high visibility. The investigation also focused on the communication breakdown caused by failing batteries in the mechanic's radio, which prevented the pilot from coordinating the boarding process via intercom.
Findings
- Lack of experience: While the crew believed the workers were experienced in helicopter operations, one worker was participating in a helicopter flight for the first time, and neither worker fully understood the dangers of their actions.
- Improper boarding technique: The decision by the workers to climb onto the skid while the aircraft was hovering created an unstable weight distribution.
- Pilot error: The pilot made a critical decision based on unverified information regarding the crew's experience and failed to implement safer alternatives, such as directing the mechanic to lead the workers to a different landing site.
Safety action
- The investigation highlighted that hovering landings for personnel boarding carry extreme risks. It is recommended that only specifically trained personnel should be permitted to enter or exit an aircraft during hover operations, except in documented emergencies.