Dont know if anyone has heard of this yet

Crack found in gearbox of Cougar Helicopters Sikorsky S-92 in Halifax - Yahoo! Canada News (http://ca.news.yahoo.com/s/capress/091102/national/chopper_gearbox_crack)

-SPAREPARTS

Ugh. So much for "It's a North Sea problem only..." :ouch:

I/C

bad news, anyone know why they r cracking?

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...:rolleyes:

Fly safe

Max

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.

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.

Would be interesting to know TSN of the affected boxes and at what power settings the affected machines are being flown.

NST

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

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

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 :mad: out of me.

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