Transport Minister warned about Robinson helicopter design problems

The main rotor (Newshub.)
The main rotor (Newshub.)

Documents obtained by Newshub show the Transport Minister was warned about design problems with the Robinson helicopter, yet when talking publicly about why they kept crashing, he blamed pilot training.

Simon Bridges stands by his comments that the high number of crashes involving "mast bumping" is down to poor education.

But a former CAA crash investigator believes it's not that simple.

Mast bumping is when the inboard end of a main rotor blade (the spindle) contacts the main rotor driveshaft (or mast).

It can result in the main rotor blades striking the helicopter's cabin, causing it to break up in-flight.

Independent crash investigator Tom McCready's been examining the main rotor of the Robinson.

He believes its multiple pivot points make it more susceptible to mast bumping than more standard designs like that on the Jet Ranger.

"It will have a much larger reaction to it because it has got three pivot points, not one," he says.

And when the Robinson reacts to a bump, he says, the consequences can quickly turn fatal.

"The transmission mounts will break because of the imbalance and that blade starts coming down through the cabin."

But Kurt Robinson, president of Robinson Helicopters, disputes Mr McCready's theory. 

"All two-bladed teetering rotor helicopters, such as the Jet Ranger and the helicopters manufactured by Robinson, are susceptible to mast bumping if not flown properly." 

He also says research has already found the tri hinge design of the Robinson's rotor makes no difference when it comes to mast bumping. 

Briefing notes to the Transport Minister appear to share some concerns about the Robinson's main rotor.

The US safety regulator, the FAA, found "excessive flapping and teetering of the main rotor... can cause the blades to contact the airframe", and that "the particular main rotor system on the Robinson 22 and 44 can make them prone to this occurring".

But the minister says he's satisfied there are no technical issues with the aircraft.

"The issue is with the education of the pilots," Mr Bridges states.

Robinson has warned pilots that "flying in high winds or turbulence should be avoided" and pilots should slow down to decrease the chance of mast bumping.

David Yeomans, who spent eight years at CAA and 15 years working for the Australian regulator, says flying conditions often change.

"The pilot and the aircraft do not control all the conditions which have been identified for mast bumping, one of the phenomena is turbulence" he says.

But Mr Robinson says pilots can avoid low-g situations and safely navigate turbulent conditions if they have proper training and follow the manufacturer's guidelines.

"As pilot control inputs are necessary to avoid and react to low-g, proper pilot training is critical to low-g mast bumping prevention." 

Transport watchdog TAIC has said it has serious concerns more mast bumping crashes involving the Robinson will occur. Last year, it called for special training for pilots of the bigger Robinson 66.

But the CAA says that's not needed - despite its own officials emailing US counterparts expressing concern that "a trend is developing on the R66 with in flight break-ups".

TAIC has also recommended that US regulator, the FAA, does more research into the design of rotor systems like that on the Robinson.

But that, like other safety ideas, is still to be considered.