MD-11 Flight Crew Operations Manual
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Hydraulics -
Description and Operation
Hyd.10.7
Land configuration is aircraft in the air, altitude equal to or less than 17,750 feet,
and slats, flaps, or landing gear extended.
During takeoff/land configurations, the HSC accomplishes the following:
• Allows the engine-driven pumps to remain on.
• Turns off the RMPs when the reservoir fluid quantity is less than 4 quarts,
or when certain multiple faults exist.
Cruise Configuration
When in cruise flight, the HSC configures the hydraulic system in the normal
configuration. Cruise flight is defined as gear, flaps, and slats retracted, or
baro-corrected altitude more than 17,750 feet.
Abnormal Operations
The hydraulic system can be placed into abnormal operations by aircraft
failures/faults external to the hydraulic systems, or by component failures within
the systems.
The aircraft failures are as follows:
• Engine fire - When an ENG FIRE handle is pulled, a mechanical valve
shuts off hydraulic fluid to both engine-driven pumps. The HSC turns off
both pumps except during the take-off and landing phase and the taxi
phase when this condition is sensed.
• Engine N2 rpm less than 45 percent - Both RMPs are turned on in the taxi
or takeoff/land phases of flight.
• Inflight engine start - When the engine FUEL switch is off, and the engine
N2 rpm is less than 45 percent, the HSC turns off both engine-driven
pumps to enhance engine rotation during starting.
• Electrical power during cruise condition - All left engine-driven pumps
are controlled by one electrical circuit and all right pumps by another
circuit. Loss of power causes all pumps on a circuit to go on. When the
HSC recognizes a failure of one of these circuits, it turns off the opposite
pumps. However, if one of the pumps on the failed circuit has low
pressure, the HSC turns on the other pump in that system.
The HSC takes corrective action to perform the following functions in response to
system faults:
• The HSC pressurizes all three hydraulic systems if the aircraft is in the
taxi or takeoff/land phase of flight.
• The HSC pressurizes two systems if the aircraft is in the cruise phase of
flight.
• Restores system pressure if the original pressure source fails and there is
adequate fluid in the affected system(s).
• Depressurizes a system with high temperature if the aircraft is not in taxi
or takeoff/land phase of flight.
October 02, 2006
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