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Chopper broke up after rotor issue: report

NZ NewswireNZ Newswire 4/05/2016

A helicopter crashed killing its pilot after breaking up mid-flight after its main rotor blade struck the fuselage in turbulence, a crash probe has found.

Pilot Mark Didsbury, 39, died in the crash in the northern Kaweka Ranges in March 2013 after the Robinson R66 experienced `mast bump'.

Mast bump is contact between the inboard end of a main rotor blade or the rotor hub and the main rotor drive shaft.

After the mast bump the rotor blade hit the fuselage and the chopper broke up in flight.

A crash investigation found the helicopter model, like the smaller R22 and R44, was vulnerable to a catastrophic mast bump under certain conditions as they shared the same main rotor design.

The Transport Accident Investigation Commission said it is likely mast bump accidents with Robinson helicopters will continue unless the dynamic behaviour of the main rotor preceding such a catastrophe is fully understood.

It said the accident was likely to have taken place when Mr Didsbury encountered turbulence while travelling at an estimate 115 knots.

At the time Robinson flight manuals did not adequately warn pilots of the hazardous operating practices and environmental conditions that can lead to a catastrophic mast bump.

The commission recommended that pilots of Robinson helicopters should avoid areas of high winds or turbulence, and stick to the manufacturer's advice to reduce airspeed if they encounter turbulence.

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