The Transport Accident Investigation Commission has found 'mast bumping' caused a helicopter to crash into Lake Wanaka in July 2018, killing pilot Matt Wallis.
The report said it's likely he encountered unexpected turbulence in mountain terrain, causing the mast to bump.
Mast bumping is when the inner part of a rotor hub hits the main rotor drive shaft, or mast. It can happen in a split second and usually causes the helicopter to break up in the air.
The commission is concerned about the number of accidents involving mast bumping in Robinson helicopters. Robinson helicopters have been on a TAIC safety watchlist since 2016. There have been more than 100 Robinson crashes in New Zealand since 2000, and more than 20 of those have been fatal.
However, TAIC is not making any new recommendations following the findings of the Lake Wanaka crash. That's because three recommendations from 2016 have already been made to address the problem of mast bumping.
It said more recorded flight data is needed from Robinsons and recorders are being developed to be installed in the helicopters.
Matt Wallis is from a well-known family of helicopter enthusiasts. His father, Sir Tim, founded Warbirds over Wanaka. Tragically, three months after Matt Wallis' death his brother Nick died in a helicopter crash. The TAIC report into that crash is yet to be released.
In a statement, Matt’s brother Jonathan Wallis said he’s relieved the investigation has concluded.
“We accept the findings of that report acknowledging that the lack of reliable evidence on the initiating cause or causes of mast bumping occurrences in Robinson helicopters continues to limit the effectiveness of safety investigations,” said Jonathan Wallis.