Executive summary
On 11 August 2008, a Kawasaki-Hughes 369D helicopter, registered ZK-HWE, departed Haast in support of a Department of Conservation track-maintenance task. On board were 3 track workers, the pilot and over 150 kilograms of equipment. The pilot had flown a similar series of flights during the previous week.
The first planned landing was at the Maori Saddle Hut, which was surrounded by high trees that restricted the approach direction. During the final approach, there was a tail wind in the range of 11 knots to 21 knots. Nearing the landing site, the pilot brought the helicopter to an out-of-ground-effect hover, where it started an un-commanded right yaw. The pilot attempted to correct the yaw, but the helicopter struck a tree and fell to the ground. There was no fire, but one passenger and the pilot received serious injuries.
The investigation found the pilot had been complacent in regard to the following aspects of flight
preparation: • not being fully involved with the loading of the helicopter, which meant he did not
assess the accuracy of the cargo weight
• not ensuring that the shoulder harnesses were accessible and worn by the occupants
• not determining that the passengers were familiar with the safety briefing.
The investigation determined that the helicopter’s engine and flight controls were operating normally, and found no evidence that a technical malfunction contributed to the accident. The helicopter was heavily loaded, but not overweight, and the flight manual charts showed that it had the performance capability to hover out of ground effect at that altitude.
The investigation determined that the un-commanded yaw and loss of control resulted from the approach being attempted under conditions that were noted in the flight manual to be conducive to a loss of tail rotor effectiveness.
The precipitating factors for a loss of tail rotor effectiveness can occur singly or in combination, and
several were present. The most significant were the weathercock stability and the loss of translational lift during a downwind approach, and the high power demand as the helicopter came to a hover.The Transport Accident Investigation Commission identified no systemic issue that contributed to the accident, and made no safety recommendations.