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S-92 gearbox crack

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S-92 gearbox crack

Old 3rd Nov 2009, 02:33
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S-92 gearbox crack

Dont know if anyone has heard of this yet

Crack found in gearbox of Cougar Helicopters Sikorsky S-92 in Halifax - Yahoo! Canada News

-SPAREPARTS
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Old 3rd Nov 2009, 12:18
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Ugh. So much for "It's a North Sea problem only..."

I/C
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Old 3rd Nov 2009, 18:20
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bad news, anyone know why they r cracking?
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Old 3rd Nov 2009, 21:54
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bad news, anyone know why they r cracking?
That's the million-dollar question that SKY is supposed to be answering. Some questions that came to my mind were (I'm sure someone on this forum can provide comments):

What specific alloy is the MGB housing manufactured from?

Is there a link between this issue and the previous AD from 2007 regarding the main transmission bolt failure?

Is there an issue with dis-similar material thermal expansion properties changing the effective torque on the mounting feet during flight operations?

Is there a background vibration issue or excessive shear force present on the mounting bolts/feet?

Is there any correlation within the HUMS data for the affected S-92a units to date that could be registered as a specific threshold signature, or are there no raw sensors close to the mountings?

Has this issue been seen before on previous helo designs, and how was it engineered out?

Now we have 2 critical areas of this MGB design that are suspect to be sub-standard, namely the filter housing studs when they were made from titanium, and now the main transmission mounting feet. Hopefully SKY will produce some answers soon before the S-92a reputation is even further destroyed...

Fly safe

Max
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Old 3rd Nov 2009, 22:15
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Is there any correlation within the HUMS data for the affected S-92a units to date that could be registered as a specific threshold signature, or are there no raw sensors close to the mountings?
That possibility, along with many others, is being actively investigated.
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Old 3rd Nov 2009, 23:57
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Has this issue been seen before on previous helo designs, and how was it engineered out?
Had occasion to ground the worlds fleet of Bell 206's when what seemed to be a crack was found on a main gear box mounting lug. Turned out to be merely a crack in the surface finish but with the facilities available on a ship at sea we did not have the means to establish that fact.
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Old 4th Nov 2009, 08:29
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Would be interesting to know TSN of the affected boxes and at what power settings the affected machines are being flown.

NST
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Old 4th Nov 2009, 08:59
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Apparently we have had a cracked lug with a gearbox in single-digit hours. Seems very odd, something has changed either a dodgy batch of castings or increased movement in the airframe for some reason. I don't think Sikorsky understand it yet.

HC
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Old 5th Nov 2009, 12:38
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I agree HC, It does seem to be happening on a particular airframe every time. (certainly in our company). At least we can rule out the fact that it's a "north sea problem only".

I currently fly the 92, Am I happy about this - no, Am I happy Sikorsky are on top of it all - yes. I also trust our engineers. Interesting how It's been happening recently & not since it's introduction.

Let's hope they can finally sort the problem soon,

BM
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Old 6th Nov 2009, 00:12
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Wow. The engineers may be on top of this, but gear boxes shouldn't crack. Ever. I thought they were considered to be primary structure, like a wing spar.

And cracking after single-digit hours??? That would scare the out of me.
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Old 6th Nov 2009, 02:48
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hullaballoo,

"The engineers may be on top of this, but gear boxes shouldn't crack"

You are spot on. An MRGB housing that carries rotor loads is a crit 1 piece of structure. As such, the casting must undergo class 1, grade A or B, 100% radiographic inspection at the foundry, with very tightly controlled acceptance criteria. And the part is also analyzed with a very conservative FoS to boot. Under these tightly controlled QA and analysis procedures, a casting structural failure would be highly unlikely.

If the failure occurred at/near a structural attachment point, I would suspect that the root cause is more likely due to an improperly installed fastener that came loose and created excessive loads on the remaining attach points.

Of course, this is all pure speculation on my part. So take it for what it's worth.

Regards,
riff_raff
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Old 29th Jan 2010, 07:38
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S 92: grounded because of cracks in gearbox

Newfoundland helicopter grounded because of cracks in gearbox housing

Published on January 28th, 2010 ST. JOHN'S, N.L. - A Newfoundland-based helicopter used to ferry workers to offshore rigs has been grounded because of a hairline crack in the aircraft's main gearbox housing.
The crack was found Tuesday in a mounting foot that is used to attach the housing to the chopper's airframe, a spokesman for Cougar Helicopters Inc. confirmed Thursday.
The helicopter, a Sikorsky S-92A based in St. John's, is the same type of aircraft that crashed off the coast of Newfoundland last March, killing 17 of the 18 people aboard.
Cougar Helicopters also operated that aircraft.
Christian Kittleson, a spokesman for parent company VIH Aviation in Victoria, said it's the second time a Cougar helicopter has been grounded because of a crack in a mounting foot.
The entire gearbox housing on a Halifax-based S-92A Sikorsky was replaced in November, he said.
The housing on the Newfoundland aircraft should be replaced by Friday, he added.
Kittleson said the mounting feet are inspected after every flight in response to a alert service bulletin issued last year by Sikorsky.
"We expected that it would happen again," Kittleson said in an interview. "It was a matter of time."
The problem is considered a "benign issue" that does not compromise the integrity of the aircraft, he said.
On Tuesday, the European Aviation Safety Agency issued a airworthiness directive that requires replacement of another part on the S-92A.
The agency said the choppers' filter bowl assembly in the main rotor gearbox has to be replaced with a newer model.
Kittleson said the company made the changes last month.
The Transportation Safety Board is still investigating the cause of last year's crash in the North Atlantic, about 60 kilometres east of St. John's. However, it has been confirmed that the chopper pilots reported a loss of oil pressure in the gearbox before losing control of the aircraft.
The Canadian agency has said studs broke on the filter assembly, resulting in the loss of a large quantity of oil.
Less than two weeks after the crash of Flight 491, the U.S. Federal Aviation Administration grounded S-92As worldwide with a directive requiring replacement of the studs.
In November, The Canadian Press obtained documents from the European agency that revealed the gearbox of a S-92A had failed a test that required it to run for 30 minutes without oil.
But Sikorsky has said it has proven to aviation authorities that the chances of an oil leak from the gearbox is extremely unlikely and that the installation of a bypass valve resolves the only identifiable cause of a main gearbox leak.
Earlier this month, the families of 15 passengers who died in the crash, as well as the sole survivor of the tragedy, reached a settlement in their lawsuit against Sikorsky.

Newfoundland helicopter grounded because of cracks in gearbox housing - Society - Canada - World - The Moose Jaw Times Herald
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Old 2nd Feb 2010, 01:41
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Kittleson said the mounting feet are inspected after every flight in response to a alert service bulletin issued last year by Sikorsky.
"We expected that it would happen again," Kittleson said in an interview. "It was a matter of time."
The problem is considered a "benign issue" that does not compromise the integrity of the aircraft, he said.
Not a very "benign" issue for us PAX up here, confidence in this helo is yet again at a low point. Explanations and engineering solutions required...

Come on guys, get this issue sorted and put to bed once and for all. This is getting tiresome.

Fly safe

Max
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Old 28th Jul 2010, 19:37
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Update?

Any updates on this Gearbox problem/solution?
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Old 29th Jul 2010, 08:58
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S92 MGB

There are a few changes recently, the latest being the reduction to the overhaul life being reduced to 1400 hours and just this last week being further reduced to 1000 hrs.
The instalation procedures for fitting the MGB have also been revised, the feet are no longer put down using sealeant UNDER the foot and they are now metal to metal contact with the airframe. With this reduction to the overhaul life I only hope Sikorsky can keep up with supplying gearboxes on time, otherwise our clients will get rather displeased with the otherwise very good S92A, when will the S92B come out.???
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Old 29th Jul 2010, 10:05
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they are now metal to metal contact with the airframe
In a offshore envirionment with a salty atmosphere I would expect this to cause dissimilar metal corrosion between the gearbox feet and the airframe.

Ask Boeing Vertol what happens in a BV234 when you have dissimilar metal in the front gearbox.
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Old 29th Jul 2010, 11:50
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Hi Grunt

The life reduction is to the casting only and is temporary. The next stage is to supply all operators with a casting with additional material around the foot. This will be an interim solution. All the cracks are on one bolt on the rear foot only. The long term solution is to use the casting from the Canadian MHP gearbox which is rated to 29k lbs plus MTOM and which will have a 4000 hour life.

All retrofit parts for all of the S-92 product improvements are supplied free to operators, even back to the first production aircraft S/N 92-006 as well as being incorporated into current production ships.

Sikorsky does not apparently want any customers to have an inferior mod state which is why the company will continue to supply retrofit product improvement parts at no cost to the customer.
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Old 29th Jul 2010, 12:02
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So the interm fix is to not use Lube? and eventually use the "MHP" Gearbox? Will that really fix the problems?
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Old 29th Jul 2010, 13:24
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Originally Posted by immaengineer
So the interm fix is to not use Lube? and eventually use the "MHP" Gearbox? Will that really fix the problems?
Do you understand the difference between lubrication and sealant? An engineer ought to. Look at what he wrote ...
Originally Posted by Grunt92
The instalation procedures for fitting the MGB have also been revised, the feet are no longer put down using sealeant UNDER the foot and they are now metal to metal contact with the airframe.
May I ask you for some clarification?

I'll offer a guess that the "metal to metal" actually has, on both the transmission deck and the gearbox, conversion coating, sealant-coating (for the gearbox, along the lines of Rockhard/Sermetel/whatever the flavor of the month is), a primer, and then paint. (If MGB isn't Mag, is that layer of coating necessary?) Or, are the feet not painted, just primed?

That isn't quite "metal to metal," is it? Maybe I am being nitpicky here.

That said, an operator's concerns about vibration and time in the salt environment are reasonably well voiced. I will guess also that sealant is applied in a healthy bead around the feet where they attach to the transmission deck. (Keep that moisture out, I say!)

Not asking you to reveal any proprietary info, just hoping to fill in a few gaps by what I assume (perhaps incorrectly) would be standard practice based on older Sikorsky aircraft.
With this reduction to the overhaul life I only hope Sikorsky can keep up with supplying gearboxes on time, otherwise our clients will get rather displeased with the otherwise very good S92A, when will the S92B come out.
I'd guess that Sikorsky folks know that from the inside better than folks on the outside.

@maxwelg2: you pose excellent questions, which hopefully the engineering team at Sikorsky will have answers for.

Last edited by Lonewolf_50; 29th Jul 2010 at 16:50.
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Old 29th Jul 2010, 13:39
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Hope - Hope seems to be something that Sikorsky don't supply to their customers as standard...

Looking back at the recent posts I see no mention of the SECOND complete foot detachment in flight. Has that really been kept under wraps?

Should this thread not be merged?
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