Mast bumping caused Matt Wallis’ helicopter to break-up inflight resulting in the fatal accident over Lake Wānaka in July 2018, according to the Transport Accident Investigation Commission (TAIC).

Matt was flying en route from Wanaka to Upper Estuary Burn Valley when the helicopter suddenly departed from controlled flight and crashed into the lake.

TAIC released its final report into the accident today (November 26) and chief commissioner Jane Meares said it is likely strong unexpected turbulence caused the Robinson R44’s main rotor disk to teeter excessively and the mast to bump.

Mast bumping occurs when a two-bladed teetering rotor head see-saws (teeters) so much that its inside edge strikes its own main drive shaft (the mast). 

It can happen in a split second, usually results in the helicopter breaking up in flight, and is fatal for those on board, the report said.

The Robinson R44 helicopter was cruising in mountainous terrain in conditions that were conducive for strong turbulence at a speed that increased the risk of an adverse outcome. 

“In this case, mast bumping caused a main rotor blade to bend down so far that it struck and entered the helicopter cabin, the helicopter broke up in flight, descended, impacted the lake, and sank,” Jane said.

Alpine Helicopters Robinson R44 in 2013. PHOTO: Patrick Weis

Matt was the sole occupant of the helicopter at the time of the accident and his body was recovered two days later.

His brother Nick was one of three people tragically killed in a helicopter crash three months after Matt’s death.

The TAIC did not make any new recommendations in the report because the three recommendations from 2016 already address the relevant safety issues, Jane said. 

TAIC’s watch list item on mast bumping already recommends concerted action to promote safe operation of Robinson helicopters.

“Operators, owners and pilots of helicopters with this type of main rotor need to know that the risk of mast bumping increases with the likelihood of turbulence, mountainous operating environments, high power settings, higher speed and light weight,” Jane said.