Incident Overview
On September 7, 2004, at approximately 17:20 local time, a Eurocopter France / Aerospatiale AS 350B3 helicopter with registration HB-ZCB crashed in the region of Cabane de Brunet, within the municipality of Bagnes in the canton of Valais. The accident occurred roughly 25 kilometers south-southwest of Sion. The aircraft was destroyed upon impact in the gorge of the Dyure de Sery river.
Operational Context and Sequence of Events
The helicopter was operated by Hélicoptère Service SA, with Dreieck Leasing SA listed as the owner. The pilot, a French national born in 1964, had been working since 06:10 that morning, accumulating approximately 11 hours of duty time and 192 rotations before the incident. At the time of the crash, the helicopter was equipped with an 18-meter load sling but carried no external load.
The pilot had transported a machine operator to the Pindin mountain construction site. After the passenger disembarked and stowed some slings in the cabin, the pilot initiated takeoff under the observation of the ground crew. While flying eastward over the plateau, the load hook collided with the terrain near the edge of the cliff. This impact caused the sling to be whipped into the tail rotor. The resulting damage to the tail rotor assembly rendered the helicopter uncontrollable, causing it to spin around its vertical axis and crash into the riverbed below.
Investigation Findings and Contributing Factors
The Swiss Federal Office for Civil Aviation (BAZL) and the Bureau for Aircraft Accident Investigation (BFU) determined that the primary cause of the accident was the collision of the load hook with the ground immediately after takeoff, which subsequently led to the sling entangling the tail rotor. The damage to the tail rotor resulted in a loss of control.
Two factors were identified as potentially contributing to the accident: 1. Fatigue: The pilot had completed a long workday, leading to reduced concentration capabilities. 2. Medication: Toxicological analysis revealed traces of Citalopram, an antidepressant, in the pilot's blood and urine. This indicated regular therapeutic use over the preceding two years. The pilot had not disclosed this medication to the aviation medical authority (BAZL). Experts noted that such psychotropic substances can impair discernment and decision-making abilities.
Casualties and Damage
The pilot sustained fatal head injuries and died immediately. There were no other fatalities or injuries among passengers or third parties. The helicopter was destroyed, and minor water pollution occurred due to fuel leakage.