PPRuNe Forums - View Single Post - Blade pitch stall margin
View Single Post
Old 9th Sep 2003, 04:49
  #13 (permalink)  
t'aint natural
 
Join Date: May 2001
Location: London
Posts: 528
Slowrotor:
I said earlier not to hang too much on that old NTSB report, but I've been loth to go into all the nauseous detail about why it's suspect. I see I'll have to fill in a few details.
At the time of the report, the NTSB was run by a man called James Hall, a political appointee of Clinton's (he'd raised a lot of money for Al Gore's Vice-Presidential campaign and got his 120,000 a year post as a reward). Hall had no aviation knowledge whatever. He was a lawyer.
Hall started out by attacking the ATR and the US commuter airlines, and he tried to ground the Boeing 737. He was on TV a lot, making a name for himself. And he went after Robinson in a big way.
The Trial Lawyers Association was at the time demanding that the NTSB give them the same access to accident investigations as the manufacturers, and Hall shifted NTSB policy in that direction. Robinson was then facing several lawsuits. One California congressman, a lawyer and a personal friend of the father of a pilot who died in a Robinson crash, went to Hall to see if he could help him overcome Frank Robinson's intransigence. (Robinson carries no litigation insurance and fights every case to the wire).
The NTSB went back over 14 years of accident data and put together the list that you have, that purports to show that Robinson helicopters would be flying along minding their own business when suddenly the rotor would inexplicably dive through the tailcone.
Every one of the accidents on that list was caused by low rotor rpm stalls, low-g manoeuvres or other known causes. The first one on the list, the pilot had turned the fuel off. In some cases they had eye-witness reports that the rotor had slowed up; in others it was obvious from the damage that the rotor hadn't hit the tailcone until after it struck the ground. There was no mystery about any of them.
A lot of field investigators at the NTSB were very unhappy with that report. The field investigators are the people who collect information, establish all the observed facts about an accident, make a wreckage distribution diagram, document the pilot's credentials and so forth. But the Board determines probable cause. The Board is made up of people like Hall, with little or no aviation knowledge. Politics and litigation intrudes where it should not. The Board was behind this report.
The reason that Robinsons were over-represented in the accident figures in the early days (they're very much under-represented today) was bad instruction. The R22 multiplied the number of people learning to fly by a huge factor. But in the USA, there weren't enough experienced instructors to handle the business.
Under the FAA rules, a fixed-wing instructor who had 50 hours on helicopters was automatically a helicopter instructor - an insane situation which was at the root of students' inability to handle many emergency situations. Fixed-wing instructors were in fact starting helicopter schools out of the boots of their cars, a situation which Robinson petitioned the FAA six times to amend before they finally put a stop to it. Here in the UK, where there was no 50-hour rule, we never had the kind of problems the US had.
The accident rates were largely brought down by Robinson's own actions, including the rescinding of the 50-hour rule, the Safety Courses, Robinson's own qualifications for insurance and other measures. The only hangover from those days is the SFAR, a face-saving measure for the Board which wasn't needed then and isn't now.
There are no more 'unexplained' accidents with the Robinson than with any other helicopter. Retreating blade stall is not something an R22 pilot need be too concerned about. The blade will not suddenly dive through the tailcone in turbulence. Keep the RRPM where they should be, react properly in case of emergency, and don't listen to ghost stories.
t'aint natural is offline