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System Operation
6. Fluid is drawn from the reservoir by the EDPs, the output being fed
to the ACO. The ACO has two modes of operation, it “cuts in” when the
system pressure falls to 220PSI and “cuts out” when the pressure rises
to a nominal 850PSI. When “cut out”, the fluid from the EDPs is returned
to the reservoir creating an idling circuit. When “cut in”, fluid is supplied
to whichever of the services are demanding fluid.
7. When a service is selected, the initial movement is satisfied by the
action of the accumulator. When the pressure falls and the ACO “cuts
in” the EDP output is fed directly to the service until no further movement
is required. With no demand on the system, pressure builds to the ACO
“cut out” value when the EDP output is returned to the reservoir through
the idling circuit.
Emergency Air System
8. An emergency air system is provided by two air bottles on the starboard
side of the fuselage just aft of the front spar. The bottles are charged to
1200PSI, an air pressure gauge is adjacent to the bottles on the starboard
sidewall. The emergency air system operates the undercarriage and
flaps in the case of emergencies. An EMERGENCY AIR operating knob,
painted black and yellow (fitted with a tell-tale wire), is to the left of the
Flight Engineer’s panel.
9. When the EMERGENCY AIR knob is pulled, emergency air is released
through shuttle valves into the undercarriage DOWN line and the undercarriage
is lowered irrespective of the position of the undercarriage selector lever.
Note:
The undercarriage cannot be raised by the emergency air system.
The undercarriage lever should still be selected down prior to landing.
10. Operation of the EMERGENCY AIR knob also releases air through
shuttle valves to the flap selector. The flaps can be lowered with
emergency air using the flap selector. However, the flaps should not be
raised except in emergency, as there is some danger of damaging the
reservoir due to the high air pressure. Furthermore, if retracted there
may be insufficient air pressure left to lower them again.
UNCONTROLLED DOCUMENT - NOT FOR USE IN FLIGHT OR TO BE PRINTED
UNCONTROLLED DOCUMENT - NOT FOR USE IN FLIGHT OR TO BE PRINTED