What happened
On August 28, 2000, a Eurocopter EC 120B with registration SE-JFY was attempting to land on a mobile helipad trailer at Stockholm/Skavlag airport, Sweden. After successfully landing the aircraft on the trailer in a headwind, the pilot opened the right-hand cabin door to verify the helicopter's position before the rotor speed had been reduced and the collective locked. During this process, the left landing gear skid unexpectedly lifted from the trailer, causing the aircraft to begin a leftward turn.
The pilot attempted to use the rotation to swing the aircraft 180 degrees to perform a new approach in a tailwind. However, as the aircraft turned, the pilot was unable to arrest the leftward yaw using the rudder. The rotation increased in rate and eventually transitioned into an uncontrolled, oscillating rotation just meters above the ground. To avoid further complications, the pilot attempted to fly out of the motion, but this worsened the instability. Ultimately, the pilot decided to terminate the flight by lowering the collective, resulting in the helicopter impacting the ground and tipping onto its right side. The impact shattered the main rotor blades and caused substantial damage to the aircraft.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft's flight controls, rotor system, and rigging. No technical malfunctions or mechanical faults were discovered in the Eurocopter EC 120B; all rigging parameters were found to be within required tolerances. The investigation also looked into the aerodynamic conditions, noting that the aircraft was lightly loaded and somewhat tail-heavy at the time of the accident.
Findings
- The pilot was properly qualified for the flight.
- The aircraft had a valid certificate of airworthiness and was a newly manufactured unit.
- The unplanned lift-off was likely triggered by the pilot inadvertently applying collective and cyclic input while securing the control stick between his legs.
- The pilot failed to apply sufficient rudder input quickly enough to stop the initial left-hand yaw.
- The aircraft's position relative to the wind likely caused aerodynamic disturbances, such as vortex interference or air recirculation, which diminished the effectiveness of the tail rotor.
- The transition into a tailwind during the maneuver likely increased the rate of rotation.