That's an easy one Lou.... That would be the "Stby Rudder Switch" or the "Alternate Flap Master Switch" and it uses the fluid in the "Baby B" res. It powers the lower rudder and bypasses system A fluid and hydraulicly extends the Leading edge flaps/slats. Alternate Flap Master uses elecrric motors to extend the flaps.

If you lose A and B hydraulic systesm you lose the upper rudder but still have manual reversion on all the other flight surfaces. Spoilers will be inoperative. The engineer has to get out the gear extension handle Push his seat in get on his hands and knees and crank. 2 turns clockwise to unlock the door uplocks and then clockwise til you get a green light. If I remember correctly.

Remember guys. This is a 3 crew airplane and it takes everyone working as a team to fly this plane. The non flying pilot handles the radios and sets up the approach and some of the checklists. The engineer takes care of the systems, performance and some of the checklists as well and monitors the approach so the two guys up frotn don't kill him.

I started as FE on the DC8 with 300 hrs total time and was upgraded to FO with 230 hrs in the 8. The engineer seat really helped me get to the right seat.  Icouldn;t have gone directly into the right seat and been succesful. It would have been too much for me to handle.

I teach in the simulator and have seen guys with 3000 hours as a flight instructor fail the sim portion. You get 4 hours in the sim before your checkride. 1.5 hours into his training he broke down in the sim and just gave up. He couldn't get used to the pace of things and how much faster they happen in a 727 than a Piper Seminole. I tried to talk him back into the sim, but he said he couldn't and he went back to flight instructuing. Not everyone makes the cut.

There are guys who are  great pilots at 500 hours and some FO's with 4000hrs that will never be upgraded to captain becasue they don't have what it takes. Pilots talk to each other the yask around if they have never flown with you before. Everyone has their favorite crew pairings. Some people work better together than others.

It's not an easy job.