Fatal chopper crash blamed on rotor hit
Turbulence likely to have triggered ‘mast bumping’ — report
Ahelicopter crash over Lake Wanaka that killed pilot Matt Wallis — three months before his brother Nick Wallis also died in a chopper crash — was caused by part of the rotor system hitting the housing below it.
Known as “mast bumping,” the problem has been cited in previous accidents involving Robinson R44 helicopters.
The Transport Accident Investigation Commission, in a report issued yesterday on Matt Wallis’ death in July 2018, said mast bumping caused an in-flight breakup of the helicopter as it flew over mountainous terrain in conditions and at a speed that put the craft at risk of an “adverse outcome” from strong turbulence.
Mast bumping is contact between an inner part of a main rotor mechanism and the housing round the main rotor drive shaft. It can happen in a split second, usually resulting in the helicopter breaking up in flight, and is fatal for those on board.
“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,” said chief commissioner Jane Meares.
It was likely strong unexpected turbulence caused the main rotor disk to teeter excessively and bump the mast, she said.
“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.”
Wallis, 39, was the craft’s sole occupant when it crashed. His body was found in the lake three days later.
He had gone on what was meant to be only a short, 15-minute flight, but was reported missing by his family’s company, Alpine Helicopters, when he did not return as expected.
Wallis’ brother and two other people were killed in another helicopter crash near Wanaka Airport in October 2018 — also believed to have been caused by mast bumping.
The final report on that accident is still some time off being published, but an interim report published earlier on the crash highlighted a major safety issue regarding the risk posed by loose items in the cabins of helicopters.
“There is evidence that a pair of over-trousers that had been packed in the cabin came out of the helicopter and became entangled in the tail rotor,” Meares said at the time the interim report was published.
TAIC has previously raised concerns about the number of accidents in NZ in which Robinson helicopters have experienced mast bumping.
It did not make any new recommendations in yesterday’s report, having previously madethree recommendations addressing safety issues.
Robinson Helicopter Companyhas updated its R44 Pilot Operating Handbook to define the non-standard term “significant turbulence” after TAIC noted the potential for misinterpretation.
Inquiries on loss-of-control or mast bumping accidents in Robinson helicopters continued to be hampered by a lack of data, the report said.
There was also a lack of understanding of how the main rotor performs in adverse conditions.
The key lesson from the investigation was that pilots needed to exercise caution when planning and conducting flights into areas of potential turbulence, and that they should seek to avoid these situations.
“Should turbulence of any strength be encountered, pilots need to take immediate action to minimise its effects,” the report said.
They should also be familiar with Safety Notice 32 and the associated video, and avoid flying in high winds and turbulence.