A "certain someone" who used to work for a major manu...okay, let's just say it...Sikorsky wrote extensively on this board about the tests SAC did with the S-92 transmission to prove that it could run "for hours" after an oil leak. However, his description of the test was a little...oh...incomplete. He did not say that *all* of the oil leaked out. In fact, there was a leak but the leak was stopped.
We later found out that the test consisted of producing a leak in the lines leading from the transmission to the oil cooler, or perhaps in the cooler itself. After detection of the leak, a bypass system was activated, isolating the oil cooler but stopping the leak. In this mode with uncooled oil of reduced quantity, the transmission was able to run for...what was the duration...2.5 hours? Which the SAC rep seemed to brag about.
What he did *not* brag about was what happened prior to that test. We learn about that from the report noted in madrock's post.
According to additional documents obtained by The Canadian Press on the same Aug. 6, 2002, test, the gearbox fell about 20 minutes short of the goal when it was run at moderate speeds after oil was rapidly drained.
But Sikorsky says it has proven to aviation authorities that the chances of an oil leak from the gearbox housing is extremely unlikely and that the installation of a bypass valve resolves the only identifiable cause of a main gearbox oil leak.
Err...how's that again?
The documents, obtained from the FAA through access-to-information legislation, (ed. note: a FOIA request) outline a discussion between American and European aviation regulators on tests of the gearbox.
The European regulators said the test showed a loss of oil would mean the helicopter could only stay in the air for "around 10 minutes," a finding Sikorsky does not dispute
.
FAA spokesman Les Dorr said the test, meant to simulate a "catastrophic loss of lubrication," was stopped at that point.
After the test, Sikorsky and the FAA agreed that the only clear risk for an oil loss would come from an oil cooler that fed into the gearbox.
Well...
A second test was then conducted on Nov. 16, 2002, to see if a bypass valve - which pilots would activate by pushing a button - would provide oil to the gearbox if the cooler were to fail. The system worked well and the gearbox kept going for hours.
So. In August of 2002 Sikorsky tested their transmission without oil. It lasted about, oh, 10 minutes. And...what a co-inky-dink, Cougar proved that to be true in their real world application of that test! SAC had to come up with
something, and three months later, by November of 2002 had devised the bypass valve, which the FAA accepted. Whether this system was "in the works" back in August is unknown at this time. But the time delay between the two tests is curious.
I'll bet that there are a couple of people within the FAA that dearly wish their signatures could disappear from the certification approval documents.
Me, I go either way on this. On one hand, I see SAC's point that transmission failures are relatively (extremely?) rare. On the other hand, it is interesting to see the lengths companies will go to creatively interpret and/or get around a regulatory requirement.
But in the name of God, who could miss that big ol' oil filter bolted to the side of the transmission? Who could look at that and *not* think that there's even a remote chance of a leak developing there? Methinks that the FAA's Les Dorr is sweating a bit right now. Or at least squirming uncomfortably.