What happened
On June 2, 2009, a Robinson 22 Beta II helicopter, registration PH-RTR, was involved in an accident while taxiing at Ameland Airport. The flight originated from Harskamp for an overland trip. Upon arrival at Ameland, the pilot encountered significant wind conditions, with winds reported at 20 knots from 340 degrees. During the taxiing process from runway 27 toward taxiway B, the pilot attempted a right-hand turn. During this maneuver, the aircraft experienced a sudden loss of directional control. The helicopter entered an uncontrolled rotation, completing a full circle. As the pilot attempted to stabilize the aircraft, a "Low RPM" warning was triggered. While attempting to bring the helicopter to a stop, the wind caused the aircraft to pivot again. The left landing gear dug into the ground, causing the helicopter to roll onto its side. The impact resulted in unrepairable damage to the aircraft and one minor injury to the passenger, while the pilot remained uninjured.
The investigation
The investigation focused on the environmental conditions, the aircraft's weight and balance, and the aerodynamic phenomena occurring during the taxi. Investigators examined meteorological reports from the KNMI, which indicated that wind gusts of up to 30 knots were present. The investigation also reviewed the pilot's flight experience, noting that she had not flown for over 90 days prior to the incident. Furthermore, the technical aspects of the aircraft's weight and center of gravity were analyzed, alongside the aerodynamic mechanics of the Robinson 22's single main rotor system.
Findings
- The primary cause of the accident was Loss of Tail Rotor Effectiveness (LTE), a phenomenon where the tail rotor fails to provide sufficient thrust to counteract the main rotor's torque.
- The occurrence of LTE was significantly promoted by a combination of high engine power demand, a heavy total weight, and a strong tailwind component.
- The aircraft was operating with a total weight and center of gravity that exceeded the limits specified in the pilot's handbook.
- The pilot failed to consult the most recent weather updates, which had predicted wind speeds and gusts that exceeded both her personal limits and the aircraft's operational handbook limits.
- The pilot did not divert to an alternative airport despite experiencing extreme crosswind conditions during the final approach, which served as an early warning of the unstable wind situation.
- The pilot's limited recent flight experience and the mental workload of managing environmental constraints contributed to the difficulty in managing the aircraft's movements.