What happened
On April 10, 2003, an Agusta A109A II helicopter, registration HB-XJA, was performing a private VFR flight toward Müstair. After departing from Sursee, the pilot decided to fly above a thick cloud layer, reaching altitudes of up to 15,400 ft AMSL. During the descent into the Müstair valley, the pilot encountered thickening clouds and increasingly diffuse lighting conditions. As the pilot reduced forward speed to maintain visual contact, a main rotor blade struck a snow-covered slope. The impact destroyed the rotor blades, causing the aircraft to lose lift and plummet vertically onto a 45-degree slope. The helicopter slid approximately 70 meters down the terrain. The accident resulted in two serious injuries and one minor injury among the occupants, while the aircraft was destroyed.
The investigation
SUST examined the flight history, weather conditions, and the physical wreckage. The investigation established that the pilot had completed several flights earlier that day and had experienced a very short rest period. Radar data showed the aircraft entered Class C and D airspace without required clearances and failed to maintain the assigned flight level due to an incorrect altimeter setting (QNH 1006 hPa instead of standard 1013.2 hPa). The investigation also noted that the aircraft operated at high altitudes for 43 minutes without any supplemental oxygen supply for the crew or passengers. Technical analysis of the wreckage confirmed no pre-existing mechanical failures, though the ELT failed to activate automatically.
Findings
- The primary cause was a collision with terrain after the pilot could no longer distinguish the ground due to diffuse lighting.
- The pilot continued VFR operations despite unfavorable visibility and deteriorating weather.
- The pilot's perception and decision-making were likely impaired by hypoxia resulting from prolonged flight at high altitudes without oxygen.
- Pilot fatigue contributed to the accident following a long period of flight activity and insufficient rest.