main rotor blade failures
main rotor blade failures
(OP)
If you are not aware the FAA has issued a sweeping airworthiness directive that requires the retirement of all R22 main rotor blades on or before thier tenth birthday. Normally, it is fatigue cycles or time in service that determines retirement. This directive is very suspicious. I've researched the circumstances that prompted this action and sadly cannot find any science to back it up. My question to the group is have any of you heard of such a thing before?
Until now R22 main rotor blades had a usefull life of 2200 hours time in service. To date there has never been a main rotor blade failure in the US. There's been three failures in Australia where the ships are used for cattle mustering. All the evidence shows these failed blade had between 3000 and 6000 hours of use when they failed. Nontheless, the FAA now claims it is the age of the blades not the time in service the caused these accidents. In my research I discovered the following:
First blade failure the age was two years old.
second failure the age was 4 years old.
third failure the age was 9 years old (the FAA says this last blade was 12 years old but Robinson told me differently when I gave them the serial number and they gave me the date of manufacture).
Anyway, the last blade was used as proof that the age of the blade is the problem and then issued this directive. What I'd like to know is if anyone has any idea what the truth is here? If it is the age that caused these failures HOW? I see no connections what so ever. Any help analyzing this would be greatly appreciated. Thanks.
Until now R22 main rotor blades had a usefull life of 2200 hours time in service. To date there has never been a main rotor blade failure in the US. There's been three failures in Australia where the ships are used for cattle mustering. All the evidence shows these failed blade had between 3000 and 6000 hours of use when they failed. Nontheless, the FAA now claims it is the age of the blades not the time in service the caused these accidents. In my research I discovered the following:
First blade failure the age was two years old.
second failure the age was 4 years old.
third failure the age was 9 years old (the FAA says this last blade was 12 years old but Robinson told me differently when I gave them the serial number and they gave me the date of manufacture).
Anyway, the last blade was used as proof that the age of the blade is the problem and then issued this directive. What I'd like to know is if anyone has any idea what the truth is here? If it is the age that caused these failures HOW? I see no connections what so ever. Any help analyzing this would be greatly appreciated. Thanks.
RE: main rotor blade failures
Mart
RE: main rotor blade failures
As a matter of information, many Bell helicopters employ blade retention straps that simultaneously restrian the blade agains radial load, and permit pitch change like a thrust bearing, but with no moving parts. These straps are all subject to a 2-year/1200 hour life limit. Everybody thinks it stinks, even Bell, but they can't afford to redesign the helicopter to eliminate the part. The 2-year life was also prompted by an accident, which resulted in an AD.
Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout
RE: main rotor blade failures
The AD list certain blades that need replacing, namely part number A016-1.
Even though it was issued as an emergency AD, you can still issue comments to the FAA. Instructions for that is also in the AD.
RE: main rotor blade failures
I know the accident to which you refer, but this is a different AD and a different accident that was related to the TT strap failure, which is not an part of the blade. The TT strap resides within the grip on the hub.
Aside from that, do Australian and Israeli authorities maintain accident investigation reports on a website? I'd be interested in reading more about any and all of these accidents.
Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout
RE: main rotor blade failures
Australian ASTB is at the first site with the accident in the second. I could not find a site for Isreal.
There has been other problems with the blades on the R22 and R44 that a special investigation was done in 1996.
http://www.atsb.gov.au/aviation/
http://www.atsb.gov.au/aviation/occurs/occurs_deta...
http://www.airweb.faa.gov/Regulatory_and_Guidance_...
http://www.ntsb.gov/publictn/1996/sir9603.pdf
http://www.airweb.faa.gov/Regulatory_and_Guidance_...
RE: main rotor blade failures
Thanks for the links, but we're still talking at cross-purposes. I gave PFF an example of life limits set by calendar time that I've encountered, but it wasn't on a Robinson. I am more familiar with Bell Helicopters than Robinsons, so I was able to give an example of a calendar life limit applicable to a BELL 212/205.
I know, PFF really wants to know about Robinsons, but I can give related examples.
So since everybody's confused, let me go over it again.
A Calendar life limit of 24 months/1200 hours was imposed on Tension-Torsion Straps in the Bell 212/205 Main Rotor Hub following several catastrophic failures. An AD was issued, and the applicability also extended to similar TT Straps in the Bell 206 series. In the past 20 years, Bell has tested the straps to death (literally), but the life limit remains in place. (I suspect that this is a chief reason that no helicopter developed by Bell in the past 15 years employs a 2-blade rotor system.)
Now that I think I've cleared that up, I can go on to the rest of PFF's concern: the FAA issuing AD's on the basis of weak/confusing evidence.
Over the past few years, Cessna 400 series (414, 421, 425, 440) owners have been fighting with the FAA over a proposed AD that would require a very costly beefing-up of the main spar. The supposed motivation for the AD is an accident involving a catastrophic failure during cruise. When examined more closely, the AD didn't actually solve the root problem (which came from the factory), and didn't even apply to models that were seemingly more vulnerable. A Damage Tolerance analysis was the basis of the "evidence", not structural tests, and it soon became apparent that the real driver was Cessna's legal department. Yup. The lawyers and bean counters added up that it just isn't worth Cessna's time to provide support for these aircraft any more. By getting the FAA to issue an AD that costs 20% of the aircraft value just to install, a bunch of aircraft go to the scrap-heap, or overseas. Either way, Cessna has fewer skeletons in the closet.
Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout
RE: main rotor blade failures
The FAA got wise and in the end, the AD wasn't issued.
Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout
RE: main rotor blade failures
If age was really a factor then why hasn't the US countryside been littered with crashed R22's? There hasn’t been one single case of a failed main rotor blade in the US! There's not another blade on the market that has a year limit. The bell blades are glued together just like the Robinsons blades but have TIS of around 5000.
Can anyone actually prove that there's a connection between age and blade failure? These data will not prove it. Not statistically or otherwise. I’ve done the statistical analysis. It’s a joke. Using these data one would have to retire the blades earlier than one year to be safe. What the data shows is that it is not age. So I ask you what the heck is going on here? Anyone have any ideas? Thanks to you all.
RE: main rotor blade failures
I've been around avaition for a real long time. This one really takes the cake. I have no idea what these guys are up to but it sure has nothing to do with safety. We've had pilots flying old blades for years. Never a problem. Now this AD. Nobody who's flying R22's can understand what this is about. I've asked a lot of engineers (rotorcraft and otherwise) and scientists about this. No one agrees with it but no one knows what the purpose really is. Don't get me wrong...if there's a real problem fine then we need to do soemthing about it. No one wants to fly a dangerous helicopter but there's just no credible proof that the age of these rotor blades has anything to do with these failures. Like I said it's like blaming bananas for broken necks. Thanks in advance for any input.
RE: main rotor blade failures
I've already banged my head on this wall, regarding the TT Straps for the Bells. The manufacturers are keeping the cards close to their chests; it's all proprietary info. They won't tell me the test methods, they won't even tell me how they make the TT Straps (although sawing through one gave me a pretty good idea).
Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout
RE: main rotor blade failures
Corrosion is manageable and there's more. The Robinson maintenance manual has a procedure for inspecting for corrosion in the very spot these failures occurred. It was titled "Main rotor spar corrosion inspection". Two months before the AD was issued Robinson issued a new page for the maintenance manual to replace this one. It's exactly the same but the title was changed omitting the word corrosion! There are more details like this associated with the issuance of this AD. All point to the same thing.
I’m familiar with the Bell grip AD and it’s just as nuts as this one. I’m told the only failure that occurred was on a ship that had had a tail strike! Some how that was translated into ALL bells. That’s crazy. This over zealous issuance of AD’s at the publics expense is out of control.
RE: main rotor blade failures
I would request the information required to prove the reasons for issuing the AD. Then point out to them that if it is unsatisfactory, members of a rotorcraft club will pay for the research then sue for any undue rotorblade replacements and costs.
If a pilot or engineer is involved in an incident they are expected to explain their decisions in minute detail and are then critisised publically when the incident report is published. Robinson, the FAA, CAA and any other authority government or otherwise should explain their actions and be held responsible for them.
Rant over, sorry for that folks but sometimes they really p*** me off.
Good luck with getting this sorted guys.
Karl
RE: main rotor blade failures
RE: main rotor blade failures
I have been associated with the commercial helicopter industrie for over 25 year's and I have seen a lot as a mechanic /pilot / test pilot. You cannot blame the FAA for having a job to do concerning safety when the factory and or the industrie will not except proper responsibilty.
RE: main rotor blade failures
RE: main rotor blade failures
http://www