Sikorsky S-92

[dik]

From the Toronto Globe and Mail:
PETER CHENEY
From Thursday's Globe and Mail
May 14, 2009 at 3:44 AM EDT

Newfoundland company orders S-92 pilots to remain below 7,000 feet
An investigation by Globe reporter Peter Cheney finds gearbox oil loss was a factor in at least four emergencies involving the Sikorsky S-92 since 2004

More than two months after a crash that killed 17 people, Sikorsky S-92 helicopters operated by a Newfoundland charter company are set to fly again, but with new altitude restrictions prompted by concerns with the main gearbox, a critical component that can stop the rotor blades. According to a memo distributed to offshore oil workers, S-92s operated by Cougar Helicopters will not be allowed to fly above 7,000 feet, reducing the time required to make an emergency landing in case of gearbox problems.

The altitude limit is the latest development in an investigative saga that has engulfed the Sikorsky S-92 since March 12, when a Cougar S-92 went down off the Newfoundland coast. Gearbox oil loss has emerged as the likely cause. A Globe and Mail investigation has revealed a troubling history of S-92 gearbox leaks, and raised questions about the way the helicopter met an advanced safety standard.

Dik

 

[Neubaten]

So, there's an advisory circular urging to substitute the titanium studs of the failing oil filter for CRES ones in every S-92.

Do you think the material change is enough to guarantee that no galling or fretting is going to appear again at the studs?

I mean, how did they get to the conclusion that the material selection is the cause of the failure and not the three stud config or an improper torqueing of the studs, initially or after a repair or substitution of the filter?

 

[MikeHalloran]

If I read what I found with Google correctly, the steel studs completely solved the chronic oil pressure loss problem for a statistically significant number of units.

Unfortunately, it took significant loss of life to upgrade the urgency of the modification.



Mike Halloran
Pembroke Pines, FL, USA

 

[Neubaten]

From what I've read there wasn't a permanent oil pressure loss, but some isolated incidents where the studs failed (because of fretting and galling), opening the oil filter and leading to total loss of oil in the Main Gear Box.

This, coupled with the fact that the machine does not comply with the FAR 29 requirement of running dry for 30 minutes, caused the fatal crash in Canada.

I am still not convinced how could they be so sure that steel studs will prevent further breakage. Please notice that the attachment of the oil filter to the MGB is based on a three-stud config (as seen on the above link).