S76 Hydraulics/Nick?
Hi Nick
Interesting to read your comments about hardovers.
About 25 years ago, when I was a young pilot, two of us were flying a Mk 1 S76, I think it was serial number 3, with barely 30 hours on type between us.
At 1000 ft downwind our Chief Pilot asked us to switch off the hydraulics in turn as a visiting Esso manager said he had felt a restriction in the controls. So we switched hyd 1 off, wriggled all the controls, felt normal, switched back on. The hyd 1 light went out. This got us thinking as it should have remained on but with 3 weeks on type we thought the a/c knew better.
By now on long finals at 500 feet, switched hyd 2 off. The right pedal shot forward, the a/c yawed 30-40 degrees to the right, the collective dropped, the cyclic went to the right slightly and we were heading for an early landing. Between us we could not move any control and decided to switched hyd 2 back on somewhat speedily. At 200 feet all was normal and we carried out a gentle running landing and the hyd light went off in the correct manner.
On back tracking down the runway, we reported this and were told to do it again. So we did. Nothing unusual happened. Put in some right pedal to turn onto the taxiway and the a/c jumped about 3 feet into the air, turned 40 degrees to the right and headed for the grass.
Reached the hangar and closed down. All the companies brains trust and the Sikorsky engineering rep, a terrific bloke, got their heads into the manuals and decided to connect a hyd rig. Nothing happened. Started up and switched the hyd 2 off at idle, nothing happened. Informed by all that I had a vivid imagination, true but not in this case! Then they asked us two to try again.
I suggested we move away from the hangar doors, just in case. Told not to be stupid. Okay says I, here we go. They all climbed in the back, I started up, 100% rrpm, switched hyd 2 off. Nothing happened, so I said watch this and put in some right pedal. The a/c jumped out of the chocks, turned 40 degrees to the right and headed for the hangar. After listening to the screams in the back, we switched hyd 2 back on. All normal again.
To make a long story longer, the machine was grounded and the Sikorsky rep suggested the tail rotor hyd should be removed for inspection at the factory.
I never got the full follow up but I believe that someone had left out some valves inside the hyd jack which allowed me to turn off the good one even though the other one did not work, thus basically giving us a full hyd failure which makes a 76 pretty difficult to fly. After this the 2 of us always did a tail rotor pedal check at idle in case another 76 had the same problem. Interestly Sikorsky also came up with the requirements for pedal checks for the next few years.
So I guess the moral is that no matter how well you know your a/c and RFM, an unusual problem can still occur that the makers have not forecast. Unfortunately I have been on the receiving end of several. One of the joys of flying a new type of helicopter!
Nick,
Do you remember this incident?