A helicopter crashed near Wellington after a loose fence wire wrapped around the tail rotor, the Civil Aviation Authority has found.
Pest control contractors 54-year-old pilot Joseph Keeley and 25-year-old hunter Cole Ritchie died while culling feral goat and deer along Transmission Gully in January.
A preliminary report from the Civil Aviation Authority (CAA) detailed how the crash of the Hughes 269C helicopter ZK-HGP occurred.
The report does not identify the men by name, but rather as pilot and crewmember.
On the morning of the crash, the semi-automatic rifle the crewmember was using stopped working, the report said, meaning the gun was no longer able to cycle ammunition.
"In line with their standard operating procedure, the pilot looked to land the helicopter so the firearm could safely be cleared."
The report said the helicopter approached a small spur with a clearing large enough for the helicopter to land in.
"The clearing in the vegetation had a mixture of long grass and low ferns, mixed with some low gorse bushes and surrounded on one side by larger gorse and native shrubs and trees. The spur landing spot dropped away sharply on both sides.
"Running parallel along the spur amongst the regenerating bush, was an old stock fence comprised of fencing wire and timber battens and posts."
A cockpit video recorder, which recorded the flight, confirmed the fence was unlikely to have been visible to the pilot or crewmember.
The fence was in poor condition, in the section where the helicopter landed it was lying low to the ground, and was obscured by regenerating vegetation.
"The helicopter landed on the spur clearing on a heading of approximately 145deg with both landing skids on the ground and engine running."
The report said as helicopter took off again, the left helicopter skid hooked a wire from the old stock fence.
"As the helicopter moved away from the clearing a strand of fencing wire came free from the fence.
"The freed wire caught and wrapped in the tail rotor, causing the helicopter to yaw heavily to the right, and despite large left anti-torque pedal input from the pilot, the yaw was unrecoverable."
The report said the helicopter experienced a loss of control and descended before impacting terrain about 100 metres away from the landing site and coming to rest, wedged against trees below a rock face and above a small creek bed.
The CAA said the initial inspection had revealed that the helicopter appeared to have struck the terrain vertically.
At the impact the right-side skid gear had separated and remained at the point of impact, while the main fuselage had rolled about five metres below the point of initial impact. The tail boom also separated from the main fuselage at impact, and came to a rest directly below the point of initial impact.
The CAA said a quantity of fencing wire was coiled around the tail rotor gearbox output shaft, tail rotor pitch control slider and tail rotor blade pitch change links.
Approximately four metres of fencing wire was also found with the main fuselage, resting across the cabin area structure.
The CAA said the main rotor gearbox was still attached to the main fuselage and the main rotor blades exhibited little to no rotational energy at the time of impact with the terrain.
At this stage of the investigation, it said there was no evidence to suggest that mechanical condition or weather were contributory factors.
The report also noted that a crash detection alert from a mobile device associated with the flight was transmitted shortly after the accident and the aircraft's emergency locator transmitter was activated, however, the signal was received by the Rescue Coordination Centre New Zealand (RCCNZ) after the helicopter had already been located.
"As we release this preliminary report, we acknowledge the loss experienced by the families, friends, and loved ones of the two men who lost their lives in January this year," a spokesperson said in a statement to RNZ.
"The purpose of the preliminary investigation report released by the Civil Aviation Authority is to provide factual information known at this stage while the investigation continues."
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