Hydraulic Power

Table of Contents:-

Normal Operations (Refer to Chaper 4)

Alternate Operations:

  • Engine Driven Hydraulic Pump Low Pressure Light Illuminated
  • Air Driven Hydraulic Pump Low Pressure Light Illuminated
  • Hydraulic System Overheat

Controls and Indicators:

  • Hyrdraulic Power


  • Hydraulic Power System
  • Hydraulic Power Control & Indication

Supplemental Information:

  • Hydraulic Power System
  • Engine Driven Hydraulic Pump
  • Air Driven Hydraulic Pump
  • Fluid Supply
  • Hydraulic Fluid Shutoff Valves
  • Hydraulic Fluid Cooling


Normal Operations (Refer to Chaper 4)

Alternate Operations:

Engine Driven Hydraulic Pump Low Pressure Light Illuminated:
Check F/E hydraulic power control module for hydraulic quantity indications and air driven
hydraulic pump indications.

Air Driven Hydraulic Pump Low Pressure Light Illuminated:
(With ADP switch in AUTO and pneumatic manifold pressurized).

Hydraulic System Overheat:
ydraulic) system overheat light illuminated or hydraulic fluid temperature above 105 C.

Controls and Indicators:

Hyrdraulic Power:

Quantity Test Switch:
Press to check hydraulic quantity indicators.
Indicators are operational when indications move toward zero, then return to initial reading when switch is released.

Air Drive H
ydraulic Pump Low Pressure Light (Amber):
Illuminates when:
- Air driven
hydraulic pump switch is in the OFF position
- Air driven
hydraulic pump is operating and output pressure is low
- ADP fails to operate (shutoff valve closed) and EDP low pressure light is illuminated.

Air Driven Hydraulic Pump Switch:
AUTO - ADP operates automatically to maintain system pressure above approximately 2600psi.
Pump will operate continuously if EDP is not operating.
OFF- Shuts off pneumatic supply to pump.
CONTINUOUS - Pump operates continuously.

Hydraulic System Low Pressure Lights (Amber):

Illuminates when system pressure is low (regardless of pump switch positions). HYD SYS PRESS 4 light remains illuminated when using hydraulic system 4 electric pump.  Note: System 4 low pressure light may illuminate during ground spoiler operation.


Hydraulic Power System

Hydraulic Power Control & Indication:

Supplemental Information

Hydraulic Power System:
Hydraulic power is supplied by four independent systems.  Each system incorporates an engine driven hydraulic pump and an air driven hydraulic pump.  The pumps, reservoir and associated components are located at the engine and nacelle area.  An electric driven hydraulic pump in system 4 is provided primarily for operation of the brake system during ground operations.

Hydraulic power is utilized for the operation of the flight control system including the trailing edge flaps, stabilizer and landing gear system including braking and steering.

The four
hydraulic systems provide power for the primary control surfaces.  Each aileron, rudder and inboard elevator surface is redundantly powered by two hydraulic systems and each of the three areas of control (roll, pitch and yaw) is powered by all four hydraulic systems.

Flight and ground spoilers are individually powered by one of three hydraulic systems.  The inboard and outboard flaps are powered by two different
hydraulic sources.

Trim movement and braking of the horizontal stabilizer is provided by two independent hydraulic motors and brakes, one pressurized from
hydraulic system 2 and the other from system 3.

Hydraulic systems 1 and 4 provide power for extending and retracting the landing gear and doors, for braking and for steering.  A separate reserve brake system is powered by system 2.

Engine Driven Hydraulic Pump:
The engine driven hydraulic pump is a variable displacement type pump with the output pressure regulated to approximately 3000psi.  The pump is capable of operating at a reduced output with engine windmilling.  The switch should be in the NORMAL for all normal operations.  Operation time in SUPPLY OFF position should be limited to five minutes to prevent pump damage.  Operational time in SUPPLY OFF position should be entered in the maintenance log.

Air Driven Hydraulic Pump:
The air driven pump operates to supplement the engine driven pump during periods of high demand.  The air pump is capable of supplying the normal system demands in the event of engine driven pump failure.  The air pump is driven by bleed air from the pneumatic system; it can be supplied from engine or APU bleed air, or ground air sources.  With the ADP switch in the CONTINUOUS position, the air pump will run continuously whenever the pneumatic duct is pressurized.  With the switch in the AUTO position, the pump will run as required to maintain a system pressure above 2600psi.
The air pump has an overspeed trip circuit that will automatically close off the pneumatic supply to the air pump.  This condition will be reflected by failure of the pump to operate normally in any switch position.  The ADP low pressure light will illuminate only when the EDP low pressure light is also illuminated, or the switch is positioned OFF.  Reset capability is not provided.

Fluid Supply:
Each system has an independent reservoir (no interconnect) with the capability of supplying fluid at all times.  To prevent pump cavitation during high demand, the reservoirs are pressurized by air supplied from the pneumatic system.  The hydraulic quantity indication system is temperature compensated to account for fluid density changes during cold soak.  Except for landing gear extension or retraction, quantity changes should be relatively small.  Retraction of the landing gear will lower the quantity in the No. 4 reservoir approximately 2.5 USG.  The green band on the indicator is primarily used for servicing.
Improper servicing can result in abnormal changes in quantity indication.  Providing there is no low quantity indication the system should operate normally.

Hydraulic Fluid Shutoff Valves:
hydraulic fluid shutoff valve located in the nacelle area controls hydraulic fluid supply to the EDP.  This valve will close when the engine fire switch is pulled or the flight engineer's EDP switch is moved to the SUPPLY OFF position.

Hydraulic Fluid Cooling:
Heat exchangers are installed in the main fuel tanks to cool the pump case drain fluid before returning it to the reservoir.  A
hydraulic system should not be operated for extended periods on the ground when the associated fuel tank is near empty.


Fill with BMS 3-11 Fluid Only


  • Systems 1 & 4:     7.5 gal
  • Systems 2 & 3:     4.5 gal. 

Normal:                     3000psi

Press LOW Lt On:   1200psi

ADP On:                    2600psi

Relief:                        3500psi.

On the ground, EDP and ADP must not be operated for more than 15 minutes when the fuel quantity is below the following quantity:

  • No. 1 and No. 4 main fuel tank: 2,500 pounds (375 gal) No. 2 and No. 3 main fuel tank: 5,300 pounds (805 gal) 

On the ground, No.4 electric pump must not be operated for more than 15 minutes when:

  • the quantity of fuel in No.4 main tank is 2,500 pounds or below. Same rule is applied to No.1 system, if installed

Hydraulic Reservoir refill point in Port Body Gear Wheel Well: Gauge, pump handle and selector valve.

Hydraulic Reservoir Filling Instructions placard