Flight and Mission Information
The helicopter, an Ecureuil AS350B3 registered as HB-ZDE, was operated by Air Grischa Helikopter SA. On 18 January 2004, it departed Samedan at 07:49 local time for Alp Trida, a ski area above Samnaun in the canton of Graubünden. The pilot was tasked with transporting explosive magazines to be placed on masts for artificial avalanche triggering. The weather was fine.
Accident Sequence
At the pick-up site, a flight assistant attached a filled explosive magazine. The pilot transported it towards the designated mast. During the rotation for placement, the pilot was unable to position the magazine on the initially intended mast and proceeded towards another mast. At that moment, the magazine exploded, causing serious damage to the helicopter. The pilot carried out an emergency landing and sustained only light scratches.
Investigation and Cause
The accident occurred at 09:35 local time. The Federal Aircraft Accident Board (BEAA) was notified at 09:50 and opened an investigation at 12:15 on the accident site in collaboration with the cantonal police of Graubünden. The investigation determined that the accident was due to an unsecured friction detonator inadvertently initiating the explosive system as a result of transport vibrations, leading to the explosion of the magazine suspended from the helicopter. The explosion damaged the helicopter to such an extent that an emergency landing was necessary.