What happened
On January 18, 2004, an AS350B3 helicopter, registration HB-ZDE, was engaged in a mission to transport and place explosive charges on masts for artificial avalanche control. The flight departed from Samedan at 07:49 LT, heading toward Alp Trida in the Samnaun region. The weather conditions were clear.
During the operation, the flight assistant attached a container filled with explosives to the aircraft. The pilot attempted to position the container onto a specific mast; however, during the maneuvering process, the pilot had to redirect the aircraft toward a different mast. During this rotation, the suspended container exploded, causing serious damage to the aircraft. The pilot was forced to perform an emergency landing. The pilot sustained only minor abrasions.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) launched an inquiry on the day of the accident, working alongside the Grisons cantonal police. The investigation focused on the sequence of events during the placement of the explosive charge and the mechanical state of the detonator components during transport and maneuvering.
Findings
The investigation established that the explosion was caused by unintended detonation of a friction-based detonator. Because the detonator had not been properly secured, the physical vibrations and jolts inherent in the transport and maneuvering of the load triggered the ignition system. This led to the immediate detonation of the explosive magazine while it was still suspended from the helicopter.