What happened
On October 12, 1963, at approximately 16:21 CET, a Bell 47G-3-B1 helicopter, registration HB-XBT, was conducting a series of material transport flights for Heliswiss Schweiz. While approaching an upper landing site at Schlegi, near Amden, the aircraft was carrying a 350 kg load of cement sacks secured in a transport net. During an attempt to release the load while hovering, a cement sack slipped over the edge of the landing platform.
In an effort to communicate with a ground crew member regarding the dropped load, the pilot decided to land the aircraft on the small platform to facilitate better verbal contact. As the pilot reduced collective pitch to descend, the aircraft's altitude dropped too low, causing the main rotor blades to strike the roof of a structure on the platform. The pilot struggled to maintain control of the aircraft following the impact, eventually bringing the helicopter to a halt on a wooden log.
The investigation
Investigators examined the landing site, a small platform adjacent to an alpine stable in Schlegi. The platform dimensions were approximately 4x6 meters, which was barely sufficient for the aircraft given that the main rotor diameter is 11.32 meters. The investigation also considered the environmental conditions, noting that while the weather was clear, the landing area was already in shadow, and local winds were present.
Findings
- The primary cause of the accident was the pilot's misjudgment during a highly demanding landing maneuver on a restricted surface.
- The landing platform was extremely small, with dimensions nearly equal to the rotor radius, requiring extreme precision.
- Reduced visibility due to the landing site being in the shade and the presence of light turbulence likely contributed to the difficulty of the maneuver.