The cause of a dramatic helicopter accident that left six Chinese tourists and a pilot injured cannot be determined, the Transport Accident Investigation Commision has found.
In its report, the Transport Accident Investigation Commission found that blowing snow from the helicopter's downdraft very likely contributed to the near collision, but it was unable to determine the cause of the crash.
The crash happened during a high altitude landing on Mount Tyndall in Otago in 2013.
The report said two Squirrel helicopters were each taking six tourists for an experience in the snow.
The first landed safely but the tail rotor of the second helicopter hit the parked helicopter's main rotor.
The second aircraft lost its tail rotor and began spinning uncontrollably around the sky, crashing about 70m away.
The pilot received a severe brain injury and minor fractures, and was unable to recall the accident.
He spent 39 days in hospital.
All of the passengers in the crashed helicopter were injured. Of the three who needed to go to hospital, two stayed in for treatment over two nights.
The report said there was no evidence to suggest that the pilot had a medical condition that contributed to the accident, but that possibility could not be excluded.
No technical or meteorological problems were found.
One other problem was cited - no emergency beacon went off in the crashed helicopter, and both aircraft landed in a different place from their original destination.
The report said it was vital that changes in destination be communicated, even though search and rescue operations had no difficulties in this case.
It also highlighted the risk of letting passengers leave a craft while the rotors are still turning.
Although this did not happen in this incident, the investigators found that is common practice with flights like these, and it called on helicopter companies to develop careful safety procedures when this is done.