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Undetermined reasons: Are Robinson helicopters too dangerous?
More than 20 years after United States safety authorities began a special safety investigation into Robinsons, debate is raging following a spate of crashes in New Zealand. Phil Taylor reports.
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The company, founded by Frank Robinson, made its first helicopter in 1979 and 12,000 more have since rolled off its production lines. Robinson is acclaimed, the recipient of the Daniel Guggenheim Medal for his "conception, design and manufacture of a family of quiet, affordable, reliable and versatile helicopters".
Yet, according to crash data, people are dying in these helicopters at an inordinate rate.
The families of those who died on the mountainside say Robinson helicopters have pushed too far towards lightness and affordability for New Zealand conditions.
It is a vexing issue. Whether the high accident rate is due to operator error, or because the unique Robinson rotor design makes them more prone to catastrophe when things go wrong, or both, is a question that carries obvious commercial implications and an emotional load for those who are grieving loved ones.
But officials expected to be dispassionate also hold concerns. In a decision heard around the world of aviation, New Zealand's Transport Accident Investigation Commission (TAIC) last October put Robinson helicopters on its watch list: the highest alert it can give.
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Citing 14 mast-bumping accidents costing 18 lives since 1991, the commission called for renewed testing of Robinson helicopters (among other recommendations aimed at promoting safe handling of the machines).
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The Department of Conservation (DoC) has stopped its staff flying in the helicopters (pending receipt of a report it has commissioned), so have Tourism New Zealand and TVNZ.
Mast bumping is contact between the inner part of a main rotor blade or the rotor hub and the drive shaft or "mast". Helicopters are not yet required to have recording devices and there is rarely eyewitness testimony or other direct evidence about what led to a mast bump.
Statements in investigation reports about probable cause are essentially the same: "The divergence of the main rotor from its normal plane of rotation for an undetermined reason."
"The Robinson rotor head will mast bump sooner than other types and the reaction from mast bump will be much quicker and more severe," Tom McCready, an engineer and veteran accident investigator, told the Herald.
In other helicopters, you may walk away with a fright and a dented mast, says the former CAA investigator. Mast-bump accidents in Robinsons in New Zealand have been catastrophic.
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A mast-bump could occur so fast, McCready says, an instructor may not be able to recover the situation when a trainee is flying.. "When it turns to shit, it turns to shit very quickly."
Robinson purposely built a helicopter for the masses and its machines have a place, says McCready. It may be that the helicopter is sometimes pushed beyond what it is designed for.
The owner of a flight instruction company that uses Robinsons, but who did not want his name published, notes they were designed as an executive commuter. Kiwis were the first to put a hook on a Robinson. They are used for mustering and deer recovery. "Kiwis being Kiwis have taken it to a whole different level. And in the right hands they are capable of doing that, but you just have to know where those limits are."
Back to McCready. "It is not a big, tough helicopter. If you relate it to motorbikes, which are also about balance and power and handling, it's a scooter. I ride a good 1200cc motorbike. They handle well, have got good brakes, the power to get you out of trouble, got all sorts of things going for them. But a scooter doesn't.
"You're on a scooter and you get between two logging trucks. Now relate the trucks to mountains where it is windy. A lot of accidents that have happened is not the fault of Robinsons but because they are Robinsons."
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Robinson says he doesn't know how McCready reached his view about the rotor head design risk. The Robinson company had looked at it "a lot and we can't find anything to it." And an FAA rotor craft panel had looked at the Robinson tri-hinge design in the 1990s and "explicitly found that it makes no difference to the susceptibility to low-G mast bumping".
However, research into the dynamic behaviour of lightweight helicopter main rotor systems was not completed because it was not thought safe to conduct flight tests of the response to abrupt control inputs.
Georgia Tech School of Aerospace Engineering subsequently worked on a computer simulation model but ran out of funds and the work was dropped in 1998 after the FAA decided it would have "limited application" and that "subsequent validation . . . would involve extensive testing with significant risk to flight safety".
In calling for unfinished testing to be reinstated, New Zealand's accident commission said it "is likely that mast-bump accidents with Robinson helicopters will continue to happen unless the dynamic behaviour of the main rotor preceding such a catastrophe is fully understood."
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Ilyas Akbari is a partner specialising in transport accidents for Baum, Hedlund, Aristei & Goldman, a Los Angeles law firm that has acted in numerous actions arising from helicopter accidents.
All of the firm's cases involving blade strikes were Robinson helicopters, Akbari told the Herald.
"Robinson Helicopters says it is operational error, you shouldn't be flying in high wind areas. But in my opinion, a lot of it also has to do with the design. If you can make the blades more robust, in addition to stiffening the vertical structure around the main rotor mast, I think it would go a long way to stabilising this helicopter."
The blades had less mass and were more flexible than comparable helicopters. "When you have less mass you have less ability to recover," Akbari says.
"I don't know how much consideration Robinsons has given that. Their position is they have 30-million flight hours and comparatively there are few accidents, when in reality per thousand hours of flight time they have by far the highest number of deaths or crashes compared to other manufacturers."
According to data collected by the independent Aviation Safety Network, the four-seater R44, for example, has been in 95 accidents internationally since January 2015, resulting in 58 fatalities. Twenty per cent of those accidents, (making up three-quarters of the fatalities), were recorded as arising from unknown circumstances.
Akbari: "One of the things that puzzles me is that there are very experienced pilots dying. It is one thing to blame the pilot but at the same time a lot of experienced pilots are dying in these helicopters."
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Wanaka helicopter instructors in September 2008. Photo/Supplied
From 2015:
NTSB: Robinson helicopter crashes have killed 19, injured 41 in Florida since 2000
Robinson mass produces helicopters and sell them relatively cheaply to the masses. There is debate whether the high number of inexperienced pilots choosing Robinson are to blame or if there is a design flaw with Robinson's three models. In any case, it seems that Robinson helicopters are disproportionately crashing. If Robinson were a car company, there'd be mass recalls everywhere.
