What happened
On 27 April 2011, a Robinson R2 22 helicopter departed from Wanaka Aerodrome for a training flight through the Southern Alps. The flight, involving an instructor and a student, initially proceeded along Lake Wanaka toward Haast Pass. After refueling at Neils Beach, the crew began the return leg toward Wanaka via the Matukituki Saddle.
During the flight, weather conditions were more severe than forecasted. A southeast wind of approximately 40 km/h, with gusts reaching 60 to 70 km/h, was creating significant turbulence on the leeward side of the mountain passes. Flight tracking data indicated the aircraft approached the Matukituki Saddle but then veered right toward the Waipara Saddle and into the Arawhata River valley. The aircraft was reported overdue that afternoon, and the wreckage was located the following day in the Arawhata River valley. The crash resulted in two fatalities.
The investigation
Investigators determined that the helicopter had broken up while in flight. At the time of the accident, the aircraft was flying at roughly 5,500 feet and was operating near its maximum allowable weight. The investigation established that the main rotor blades deviated from their normal plane of rotation and struck the tail boom, which led to the separation of the tail rotor assembly.
Several contributing factors were identified as potential causes for this deviation, including the impact of moderate to extreme turbulence, the possibility of the main rotor speed dropping below its minimum limit, or the pilots executing large, abrupt control inputs during the flight.