A New Plymouth pilot and flight examiner who survived a mid-air emergency in a Robinson helicopter says the chopper's design needs further investigation.
Jim Finlayson was forced to put the helicopter into a barrel roll when the rotor blade hit the body of the air craft.
As he hit 1200 feet on a training flight, his Robinson R22 suddenly pulled to the right. Mr Finlayson called the incident "incredibly scary".
An incident report showed what's known as a 'mast bump' - where the rotor blade hits the mast that holds it up.
That can turn deadly if the blade then strikes the cockpit, but Mr Finlayson stayed in control.
"I managed to do a complete fairly untidy barrel roll and fly out of that manoeuvre which is something a helicopter is never designed to do, or should or could have done," he says.
Eighteen people in New Zealand have died in mast bumping crashes in the past two decades, but unexplained in-flight break ups have occurred overseas too.
Robinson blames poor training of Kiwi pilots, claiming turbulence coupled with pilots reacting wrongly on the controls can cause a mast bump.
Mr Finlayson thinks there's more to it as his incident occurred on a calm day with no turbulence.
"There's something else going on. It can also happen in normal flight conditions and I would be weary of always blaming the pilot for putting incorrect control inputs in," says Mr Finlayson.
"Pilots have a very healthy sense of self-preservation. They don't tend to do things that are going kill them."
The Transport Accident Investigation Commission and the US safety board have called for more investigation into the design of the main rotor.
Robinson says that work in 1994 showed the rotor design doesn't make it more susceptible to mast bumping.
However, subsequent studies have recommended more scientific testing be done. That's never happened.
"I think the big thing that needs to change is this investigation into what exactly is going on with the rotor design of the Robinson helicopters," says Mr Finlayson.
Mr Finlayson still flies his Robinson and trains students. He knows raising questions about the aircraft design could ultimately cost him business.
But as he's one of just two Kiwi pilots documented to have survived a mast bump, he thinks it's worth it.