What happened
On August 12, 1995, an AS 350B2 helicopter, registration HB-XVT, was conducting a private transport mission in the Klöntal region of Switzerland. The flight involved a private pilot and an experienced second pilot acting as a safety observer. After landing on a small, grassy alpine meadow at Mittel Stafel to deliver passengers and pick up cargo, the second pilot exited the aircraft to assist with the load.
As the cargo was being brought to the helicopter, the pilot attempted a sudden takeoff. During this maneuver, the aircraft experienced a sharp nose-down movement and a significant pitch change. The main rotor blades struck the rising terrain, causing the helicopter to spin 90 degrees and crash. The pilot sustained fatal injuries during the impact.
The investigation
The investigation focused on the sequence of events during the takeoff and the communication between the crew members. Investigators examined the aircraft's technical condition, the landing site, and the flight logs of the involved pilots. The wreckage showed that the main rotor blades had been sheared off at the head due to the impact with the ground.
Physical evidence at the site confirmed that the landing area, while relatively small and slightly sloped, was otherwise unobstructed. The investigation also reviewed the pilot's flight experience, noting discrepancies in reported flight hours, and examined the lack of clear operational agreements between the individuals involved in the flight organization.
Findings
- The primary cause of the accident was an uncontrolled and uncoordinated takeoff maneuver.
- The pilot likely inadvertently pushed the cyclic control forward, causing the rotor disk to tilt toward the rising slope.
- The pilot reacted to perceived vibrations by pulling the collective pitch lever aggressively and without coordination.
- There was a lack of clear and complete communication between the involved parties before and during the flight, leading to confusion regarding command authority.
- The pilot was not wearing a protective flight helmet; investigators concluded that the fatal head injuries likely could have been avoided if a helmet had been worn.
- No technical defects or mechanical failures were found in the aircraft's systems or components.