Sikorsky In Hot Water Over Run-Dry Test
Cougar Sikorsky S-92
The loss of oil pressure to the main gearbox of Sikorsky’s S92 helicopter has become the focal point of recent accidents. The S92 crash that killed 17 last March was blamed on this problem. Things are getting even more interesting now as information surfaces about their FAR Part 29 certification. One of the tests to get that certification is a 30 minute run-dry test of the main gearbox. Sikorsky failed that test only 10 minutes in. How did they still get the Part 29? Sikorsky argued that the loss of oil to the assembly would be “extremely remote” which means the statistical failure rate shouldn’t be worse than 1 in 10 million flight hours. This allowed them to get an exemption for that test despite a recent Globe investigation saying that the failure rate is actually 267 times that. In response to failing the test, Sikorsky added a valve to allow bypassing the oil cooler as they thought that would be the most likely location of a leak. The problem is that that isn’t the only place oil could have leaked out. In the case of the crash in March it was because of the failure of titanium bolts that hold the oil filter in place. No valve exists that could have helped in that scenario so it’s likely, at the most, the helicopter could have stayed airborne for only ten minutes.
To add to the drama, Sikorsky made it a big point in their S-92 brochures that they were the first helicopter to be Part 29 certified. There is no mention that they didn’t actually pass all the tests. Pilots flying the aircraft were likely operating under a false sense of security and were unaware that the run-dry capability was far less than what the Part 29 standard calls for. If it turns out that that is indeed the case, I suspect Sikorsky is going to be in for some litigation.
Check out this technical information document on the S92 – if you scroll down you’ll see this written under the safety features section:
30-minute drive
system after oil
leak and 140%
over-torque
certification
Good luck explaining that one Sikorsky…
