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A300Capt · January 23rd, 2003, 20:04

The HDG is found mostly in twin engine aircraft used for ETOPS. It's a 4th power source for AC/DC power in the event you lose the engine/APU driven generators. It basically works like an internal RAT using hydraulic power to turn and usually powers such things as the Captain's instruments, FMC, IRS's and it's operation is normally fully automatic.

The RAT on the B757 is designed to deploy automatically in the event of a dual engine failure inflight and it only provides hydraulic pressure to the flight controls.

January 23rd, 2003, 20:04	#6
A300Capt Senior Member Join Date: Oct 2000 Location: Louisville, Kentucky Posts: 707	Re: Not suppose to happen.... The HDG is found mostly in twin engine aircraft used for ETOPS. It's a 4th power source for AC/DC power in the event you lose the engine/APU driven generators. It basically works like an internal RAT using hydraulic power to turn and usually powers such things as the Captain's instruments, FMC, IRS's and it's operation is normally fully automatic. The RAT on the B757 is designed to deploy automatically in the event of a dual engine failure inflight and it only provides hydraulic pressure to the flight controls.