What happened
On June 18, 2008, a Eurocopter AS350 B2, registration HB-XVB, was performing a private VFR flight near Grenchen Regional Airport. The pilot, having completed a training flight earlier that morning, was returning to Bern when a low fuel warning activated. Due to a desire to reach his destination in Zurich quickly, the pilot decided to land at Grenchen to refuel.
At the time of the incident, the airport utilized a procedure where helicopters without landing gear would land on a mobile platform to be moved to a fuel station. During the approach, the air traffic controller instructed the pilot to land specifically on the platform at helipad H1. As the pilot attempted to position the aircraft, he relied heavily on a rearview mirror mounted on the right skid to judge the distance from the platform's edge.
Upon contact, the aircraft began to bounce and drift. The left skid eventually slipped off the edge of the platform and made contact with the ground. In an attempt to lift the aircraft by increasing collective pitch, the pilot inadvertently caused the helicopter to rotate rapidly. The aircraft's lateral tilt increased until the main and tail rotors struck the ground, causing the helicopter to overturn on its right side. The impact led to the disintegration of the rotor components and caused one injury to the pilot.
The investigation
SUST examined flight recordings, radio communications, and witness statements. The investigation focused on the landing sequence, the dimensions of the mobile platform, and the pilot's visual techniques. Investigators noted that the pilot was monitoring the landing primarily through a mirror, which limited his perspective of the aircraft's position relative to the platform edges. The investigation also reviewed the airport's refueling procedures and the regulatory environment regarding mobile platforms at the time of the accident.
Findings
- The primary cause of the accident was the loss of control during landing on a mobile platform, which led to the aircraft overturning.
- Inadequate fuel planning contributed to the need for the unscheduled landing.
- The refueling procedure itself required landing on a mobile platform, which introduced inherent risks.
- The pilot had limited recent training regarding landings on such platforms.
- A sense of time pressure influenced the pilot's decision-making process.