MD-11 Flight Crew Operations Manual
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Hydraulics -
Description and Operation
Hyd.10.4
Rudder Standby Power/Non-Reversible Motor Pumps
Two Non-reversible Motor Pumps (NRMP) provide an alternate source of
hydraulic power to the rudder and horizontal stabilizer when the primary
hydraulic system cannot provide power. Hydraulic system 2 powers the upper
rudder and horizontal stabilizer via the 2-1 NRMP when hydraulic system 1
cannot provide power. Hydraulic system 3 powers the lower rudder via the 3-2
NRMP when hydraulic system 2 cannot provide power.
A compensator is installed for each NRMP. Low NRMP compensator fluid level
automatically disarms the affected pump.
NRMPs operate when the primary system pressure falls below 2,000 psi ±200 psi.
The NRMPs stop operating when the primary system pressure rises above 2,000
psi ±400 psi.
The NRMPs are always armed in flight. The HSC disarms the NRMPs only during
ground maintenance via input through the Multifunction Control Display Unit
(MCDU).
Hydraulic System Enhancement
A check valve and motor-operated shutoff valve in hydraulic system 3 enhances
system integrity if there is an uncontained failure of engine 2. The installation uses
reservoir level sensing to detect leakage, and automatically shuts off system 3
elevators and 3-2 NRMP when the fluid in the reservoir reaches a predetermined
level. This action retains enough fluid in hydraulic system 3 for pitch and roll
control through use of horizontal stabilizer trim and lateral controls powered by
system 3. The HYD 3 ELEV OFF alert is displayed when the shutoff valve closes.
Flight Control Bypass Valve
A hydraulic system 3 flight control bypass valve isolates its associated flight
control actuators from pressure when the rest of the system is pressurized. This
valve is controlled by the HSC only during ground maintenance via input through
the MCDU.
Automatic Operation
The HSC automatically controls the hydraulic system. The HSC calculates aircraft
flight phases and configures hydraulic components as necessary.
Normal Configuration
Normal configuration is as follows:
• Engine-driven left pumps on.
• Engine-driven right pumps armed.
October 02, 2006
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