Flight instructor Graham Stott (31), of Wanaka, and commercial pilot trainee Marcus Hoogvliet (21), of Queenstown, died after the Robinson R22 broke up in midair on the return leg of a flight to Mt Aspiring National Park on April 27, 2011.
Yesterday, the Transport Accident Investigation Commission released the findings of commissioners John Marshall QC, and Helen Cull QC.
Families of the two men said they were pleased the report proved there was no negligence on behalf of the men.
Stott family spokesman Corey O'Leary told the Otago Daily Times ''that is quite satisfying for us ... it was a freak occurrence''.
The report said the helicopter was near its maximum weight and flying at a relatively high altitude in strong winds and moderate to extreme turbulence when it broke up in flight.
''The boys were caught in the wrong place at the wrong time,'' he said.
Mr Hoogvliet's father, Henk, said the report confirmed what the family already knew.
''They experienced an extreme wind event that overwhelmed the helicopter and from which they were unable to recover.''
The commission found the break-up was caused by the main rotor blade striking the tail boom and severing the tail rotor, meaning the crash was ''inevitable''.
Mr O'Leary said while there had been criticism of the length of time the final report had taken, the family was grateful it was ''thorough and accurate''.
He said it had been a difficult period for the Stott family, but ''we can move forward remembering the good times''.
Henk Hoogvliet said ''as a family, although greatly saddened, we have no regrets''.
''Marcus ... spent the happiest four months of his life learning to fly.''
The family had made a donation towards the Search and Rescue building under construction in Wanaka, in recognition of their assistance in difficult and dangerous conditions.
The report said the instructor was ''possibly unaware'' of the dangers of flying an R22 close to its maximum permissible weight.
The helicopter was at 5500ft above sea level and on ''an unexpected deviation from the intended flight path'' when it crashed.
The reason for the change in flight path could not be determined, the report said.
The wreckage was consistent with the pilot losing control after the tail rotor was severed by ''successive strikes'' of the main rotor on the tail boom.
Toxicology analysis of the pilots showed no evidence of alcohol or drugs. It could not be determined who was flying the helicopter when it broke up.
The report recommended the director of Civil Aviation review safety training for pilots of Robinson helicopters and adopt any measures which would make them safer to operate in New Zealand.
It also recommended the director encourage the use of in-flight tracking devices and continue to support international work to improve crash survivability of the devices.
The report said since the Civil Aviation Authority reduced safety awareness requirements in 1998, New Zealand had an average of one R22 in-flight break-up accident every 18 months since 2002.
The CAA accepted the commission's findings, and would now work to put those recommendations in place.
The New Zealand Helicopter Association said it was not in a position yesterday to discuss the findings.
- Additional reporting by Tim Brown
