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main rotor blade failures

main rotor blade failures

main rotor blade failures

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.

RE: main rotor blade failures

Hmmm, it does seem rather odd. The only time related reasons i can think of are either corrosion or deterioration in UV light. I have never actually seen either affect aero components. The other possibility is that ten years ago Robinson introduced a modification to overcome the failure problem. The FAA may just be trying to wipe the slate clean...


RE: main rotor blade failures

I read an NTSB report on that very topic last month.  The rate of loss-of-control accidents on the Robinsons is very high (factor of 100).  Some blame can be given out to the low time the Robinson pilots tend to have.  Also, it was being compared to commercially operated machines with elaborate maintenance facilities backing them up.  So I didn't think the comparison was fair, but the flat statistics are alarming.  I can dig up the report if you like.  It's somewhere on www.ntsb.gov.

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 tells you the reason it was issued. It is due to two accidents in Austtralia and Isreal. Corrosion from water penetration initiated a fatigue crack in the blade.

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.


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

Thanks to all of you for your replies. Yes I've been in contact with all the authorities on this since the AD was issued. It's been an ongoing investigation of mine. I've accumulated a mountain of data and information. The truth is the AD has nothing to do with the failures in Australia and I can prove it. The FAA claims they have been watching the activity in Australia for 14 years now. The first failure came in 1990. The blades were used for cattle mustering and had been grossly over flown but were only 2 years old. The second accident (2000) same thing, grossly over flown blades but they were only 4 years old. The third (2003) again same thing only this time the ship had been bought by a training outfit but previously used for cattle mustering. The blades were over flown but were only 9 years old. Now the FAA claims the last blades were 12 years old but in every case I obtained the serial numbers from the Australian authorities and called Robinson and found out when they were manufactured. The ages were 2,4 and 9 years. There you have it. Where’s the 10 year age limit come into this?  In every accident the blades failed in the spot where normal fatigue failure occurs and keep in mind these blades were all over flown big time and used for cattle mustering. Now if the concern really is corrosion why not just inspect? I proposed a method of doing this that would have worked just fine. The FAA rejected it. An attorney wrote the response because it did not address my AMOC request. Instead it was a deflection. And coincidently at the same time the AD came out Robinson had a new rotor blade to sell! How convenient! I've requested metallurgical analysis, fatigue analysis etc. on all these blades to find out just what happened. And guess what....I still haven't received one shred of evidence from them. NOTHING! My guess is there never was any REAL science done here at all. Appearently they didn’t even bother to check the ages of the blades before issuing the AD.
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

Let me restate what I mean by "I can prove it". What I mean is the data the FAA refers to, as the reason does not support the conclusion in any way. So the proof is obvious. It's like outlawing bananas because of broken necks.
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

Corrosion leading to cracks that cause fatigue failure is driving this AD.  The FAA may have arrived at the 10 year figure from numerous methods, such as testing in a salt-spray chamber or examination of old blades that have been scrapped when they reached their life limits.  If this is how they did it, then the information would have come from Robinson, so they hold most of the cards.  Robinson would not be willing to divulge that information.  If Robonson saw the writing on the wall a while ago, they would have had time to initiate product improvement, too.

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

It's true that the FAA claims it's corrosion but it's a coincidence that the last failure had corrosion. When I talked with them about this they quickly pointed to the previous failures as if they were an integral part of the AD. And what would they have come up with if the last failure had no corrosion? There would have been another excuse. Think about what this AD says. The way it's written I could buy a set of blades leave them in the box for ten years and on the day after they turn ten they are going to fail. Totally ridiculous! For this to be true the corrosion problem would have to start at the factory in which case there should have been a recall.
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

Sorry to be devils advocate, but this kind of thing is happening in the UK too. In fact the CAA/JAA/EASA (whatever this months title is) will follow the FAA with or without any evidence.
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.

RE: main rotor blade failures

Thanks for your reply Karl. I agree and have done as you suggest...actually right from the start of this nonsense. I will not stop either because it's wrong and an abuse of power. The truth is there is no evidence at all. It's junk science at best. They try to make a connection between accidents caused by abuse with rotor blade age. Totally absurd! I have much information if your interested I'd be happy to share it with you. Please let me know.

RE: main rotor blade failures

Rotor blade design that is associated with the robinson helicopter is very complicated . The robinson helicopter tracking and balancing requirment is very exacting and that there is no other helicopter blade syatem that utilize's these component's on the R-22 / R44.  I have talked with people in and around the factory to colaborate the fact that it is very difficult to get a R-22 in perfect balance.
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

Gentlemen, There have indeed been pre 1990 failures of the main rotor blades on the R-22. Certain s/ns were pulled from service in the early '80's. The fault of "poor QC". This was after a fatal crash. Regarding the TT straps on the Bell 206's. There were catastophic failures in the gulf of mexico in the late 70's. We were down to a 300 hr Strap replacement for awhile.As I recall, this only applied to salt atmosphere ops. The info we got in the field, (strictly anedotal ) was that the elastomer was changed at some point ( the old formula killed some lab rats we were told ) and the new elastomer coating the straps caused corrosion. I personally observed a 600ish hr strap cut apart in the "Bell Shop" and saw corrosion in the stainless steel wires.Looked like your granney's battery terminal. The Cessna Spar AD was referenced- C421C800 & on, and all 425's have had an AD for years now. They differ markedly from earlier models. What is interesting, is the latest failure ( on that 402C ) did not occur in the area predicted by the much discussed Cessna study. Oh well, back to the drawing board. I personally don't think this spar business is driven so much by the legal department, as by the desire to create a profit center from the huge labor required to install the service kits.

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