MD-11 Flight Crew Operations Manual
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Hydraulics -
Description and Operation
Hyd.10.8
• Depressurizes a system when its reservoir quantity drops to 2.5 gallons
(9.46 liters) if the aircraft is not in taxi or takeoff/land phase of flight.
• Turns off a source of excessive pressure and substitutes one of correct
pressure if the aircraft is in the cruise phase of flight.
When the aircraft enters the land phase, these systems are repressurized, if the
reservoir fluid level is greater than 1.0 gallon (3.78 liters).
Fault Priorities
A system of priorities is established for execution of abnormal/emergency
procedures by the HSC. For conditions with equal priority, the first condition
detected has priority.
The procedure for the highest priority condition is executed when it is detected.
Any procedure for a lower priority condition that may be in progress at that time
is aborted.
Once the procedure for a higher priority condition is completed, normal
monitoring resumes and a lower priority procedure is restarted if still applicable.
The priority sequence is as follows:
1. Loss of fluid (reservoir fluid <2.5 gallons).
2. Engine fire.
3. Inflight engine start.
4. Engine N2 rpm less than 45 percent.
5. System pressure low or high.
6. System temperature or engine-driven pump case drain temperature high.
7. Engine-driven pump pressure low.
8. Engine-driven pump electrical power loss.
Reversion To Manual Mode
The HSC reverts to the manual mode if:
• Manual is selected.
• Both HSC channels fail.
• Tripple hydraulic failure occurs.
• Dual hydraulic failure occurs and at the same time an EDP fails in the
remaining system.
• More than four EDPs are required to be commanded off because of
detected failures.
EIS Test Display
All hydraulic synoptic data digits are crossed with amber X’s when all of the
following conditions are met:
• The aircraft is on the ground and operational.
November 10, 2008
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