What happened
On May 7, 2001, an Aerospatiale AS350 B2 helicopter, registration SE-JCA, was performing a utility flight at Vidsel airport in Sweden. The pilot attempted to land the aircraft on a specialized helicopter-landing trailer. After successfully touching down on the trailer bed, the pilot initiated an ascending hover to adjust the aircraft's position on the trailer.
During this maneuver, the flexible steel strip on the right-hand landing skid became snagged on the edge of the trailer's landing bed. When the skid suddenly broke free, the helicopter experienced a rapid, uncontrolled yaw to the left. The pilot attempted to correct the rotation using right rudder but was unable to arrest the movement, leading the pilot to suspect a tail rotor malfunction. As the aircraft rotated approximately 180 degrees, the tail rotor struck the trailer. The subsequent impact with the ground caused the aircraft to overturn onto its right side, resulting in the separation of the rotor transmission and the destruction of a rotor blade.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the wreckage and the landing equipment. Technical inspections of the Aerospatiale AS350 B2 revealed no mechanical or technical faults that contributed to the accident. The investigation also focused on the design of the helicopter-landing trailer, noting that the landing bed consisted of two parallel plywood sheets with a significant gap between them. Furthermore, investigators analyzed the aerodynamic conditions, noting that the aircraft was operating in a right-quartering crosswind, which can impact tail rotor effectiveness.
Findings
- The right-hand landing gear skid became entangled with the edge of the landing trailer.
- The design of the helicopter-landing trailer was unsuitable for this aircraft type due to the gap in the landing bed.
- A transient aerodynamic disturbance of the tail rotor function may have occurred during the hover.
- The pilot's chair became detached from the cabin floor due to the forces of the impact.