'Mastbumping' led to fatal helicopter crash in Kahurangi National Park - TAIC

Thursday, 30 March 2017

A helicopter which crashed into steep bush in Tasman District's Kahurangi National Park, killing the pilot, broke up in flight after a rotor blade struck the cabin, a report has found.

The Robinson R44 helicopter dropped off flight radar over the park, 35 kilometres west of Motueka, on the morning of October 7, 2014.

The body of pilot Damian Webster and the burnt wreckage of the helicopter were found three days later.

Webster had been flying the helicopter from Karamea to Nelson for routine maintenance and was the sole occupant.

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The crash occurred after one of the main rotor blades struck the cabin and the main rotor assembly separated from the rest of the helicopter, the report from the Transport Accident Investigation Commission (TAIC) found.

The TAIC said the rotor strike, followed by its break away, was caused by 'mast bumping'.

This was where an excessive teetering or 'see-saw' movement of the main rotor causes the inner end of the blades to contact the main rotor driveshaft — or mast — while rotating.

'It is difficult to determine the exact sequence of events that lead to severe mast-bumping and in-flight break-ups, as they are always fatal and happen extremely quickly,' the report says.

'The level of destruction and the historical lack of witnesses or any recording devices on light helicopters make the task of analysing break-ups difficult.'

The report also found that it was not possible to establish whether Webster's actions had contributed to the in-flight break-up, saying 'it could not be excluded as a potential factor'.

WEATHER CONCERNS

Before leaving Karamea, Webster told another pilot and the owner of the helicopter that he was concerned about high winds in the area he would be flying, the report says.

The pilot advised him to follow the Karamea and Crow rivers so he crossed the Tasman Range south of Mount Arthur, which was clear of cloud.

Webster left Karamea aerodrome about 7.40am, but he took a different route.

He followed the Leslie River up to the Tablelands area to the west of Mount Arthur, before flying up the Flora Stream towards the Flora Saddle.

The report says that Webster likely encountered moderate to severe turbulence and a 'severe downdraught' during the flight.

The crash happened at 8.08am, according to on flight tracking data.

THE SEARCH

A large-scale search operation involving several helicopters was hampered by bad weather and challenging terrain.

On the fourth day of searching, one of the crew spotted a sheet of paper in some trees which led to the discovery of the wreckage, about 1.5 kilometres south of the Flora Saddle.

Webster, a builder, moved to Karamea from Marlborough four years before his death.

He had a private pilot license and 287 hours of flying time, of which 65 hours were completed in helicopters.

He learned to fly in Nelson, and was a father of one son.

The TAIC has recommended extending limitations to operating Robinson helicopters in strong winds and turbulence.

Robinson Helicopter Company released a statement saying that it disagreed with much of the TAIC's report.

It said the report contained 'numerous technical errors and incorrect assumptions'. The company suggested that Webster's lack of experience could have contributed to the crash.

'The accident pilot's very low experience level flying helicopters and the fact that the flight was conducted at the behest of a potential future employer may have combined to make the pilot attempt a flight beyond his experience and skill level,' the company said.

It also said external cargo pods, which were not factory tested, fitted to the helicopter may have affected the helicopter's handling in high winds.