Incident Overview
On June 16, 2017, at approximately 17:50 local time, an Airbus Helicopters AS350 B2 (registration HB-ZPF) involved in a training flight suffered a loss of tail-rotor effectiveness while performing a hover taxi at Luzern-Beromünster airport (LSZO). The helicopter was undamaged, and no injuries were reported among the two crew members and four passengers.
Sequence of Events
The training flight was the pilot's second session aimed at obtaining a type rating for the AS350. The helicopter was operated near its maximum take-off mass of 2250 kg, carrying the instructor and pilot in the front seats and four passengers in the rear. After lifting off from a helipad at the southern end of a hangar, the helicopter crossed the grass runway in a hover taxi southward toward the threshold of runway 33 for a departure to the northwest. The instructor was controlling the helicopter. Visibility was good, with a light gusty wind from approximately 330 degrees at about 15 knots.
As the helicopter hovered over the beginning of the glider runway, a fixed-wing aircraft was taxiing into position on runway 33. The instructor later stated that, to avoid downwash from the main rotor affecting the other aircraft, he intended to yaw the helicopter left around the vertical axis. When he subsequently applied right pedal to realign the helicopter to the northwest, the tail rotor suddenly lost effectiveness. The helicopter began an uncontrolled rotation to the left (counterclockwise) of slightly more than one full turn before the instructor managed to stop the rotation and execute a gentle landing on the grass. During this event, an over-torque of 113% occurred for approximately one second.
Aircraft and Personnel
The helicopter was owned by HRM Helicopter und Immobilien AG and operated by Airport Helicopter AHB AG. The flight instructor held a Swiss commercial pilot license for helicopters (CPL(H)) with a total of 3885 flight hours, including 429:53 hours on the accident type. The pilot held a Swiss private pilot license (PPL(H)) with 120 total hours, of which 5 hours were on the AS350. Both licenses were issued by the Federal Office of Civil Aviation (BAZL).
Outcome
A subsequent visual inspection revealed no need for repairs. The Swiss Transportation Safety Investigation Board (STSB) conducted a summary investigation in accordance with Article 46 of the Ordinance on the Safety Investigation of Transport Incidents.