MD-11 Flight Crew Operations Manual
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Hydraulics -
Description and Operation
Hyd.10.5
• Reversible motor pumps (RMP) off.
• Auxiliary pumps off.
• NRMP rudder standby power armed.
• Flight control bypass valve open.
Normally, only the left engine-driven pump in each system operates. The right
pump is controlled by an armed circuit external to the HSC, which turns on the
right pump if the left pump pressure falls below 2,400 psi. The HSC also monitors
this function and turns on the right pump if the external circuitry fails to do so.
Hydraulic Preflight Pressure Test
The hydraulic preflight pressure test, the first of two preflight tests required to test
the hydraulic system, is performed only before engine start, and uses system 3
auxiliary pumps and both RMPs. The following conditions must be satisfied in
order to start or continue the test:
• Aircraft is on the ground and all engine FUEL switches are off.
• Hydraulic fluid quantity in each system reservoir is more than a
predetermined value, and the quantity transmitters are operative.
• Flight control bypass valve is in the normal position (open).
• System pressure sensors are operative.
• System pressure is less than 1,000 psi when the test is started.
• Auxiliary pumps are off when the test is started.
• Auxiliary pumps are not operated manually by anyone in the cockpit
during the test.
• AC ground service bus is energized.
The pressure test can be initiated only by the flight crew. This is necessary to
assure proper safety clearance before pressurizing hydraulically powered
components. When the HYD PRESS TEST switch is pushed, a series of
commands, sent by the HSC, accomplishes the following:
• Performs internal HSC checks for about the first 45 seconds.
• Verifies each auxiliary pump independently produces at least 2,400 psi.
• Verifies RMP 1-3 is able to produce at least 2,400 psi in system 1 and that
the associated shutoff valves operate correctly.
• Verifies RMP 2-3 is able to produce at least 2,400 psi in system 2 and that
the associated shutoff valves operate correctly.
• Verifies hydraulic fluid quantity in each system reservoir is at least 3.8
gallons (14.38 liters) with the system pressurized.
• Verifies engine pump pressure low switches function correctly while the
pumps are depressurized.
October 02, 2006
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