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Section - III
SYSTEMS DESCRIPTION
Sub-section 5
HYDRAULICS
Table of Contents
Page

GENERAL.......................................................................................................5-3
MAIN HYDRAULIC SYSTEM.......................................................................5-3
AUXILIARY HYDRAULIC SYSTEM.............................................................5-3
MAIN SYSTEM ...............................................................................................5-4
FLUID STORAGE ........................................................................................5-4
POWER GENERATION...............................................................................5-5
High Pressure Relief .............................................................................5-5
Low Pressure Indication ........................................................................5-5
Hand Pump ...........................................................................................5-5
MAINTAINED PRESSURE PATHS .............................................................5-5
Thrust Reversers...................................................................................5-5
Wheel Brakes Emergency Path ............................................................5-6
Accumulators ........................................................................................5-6
NON-MAINTAINED PRESSURE PATHS ....................................................5-6
Figure 1 - Main Hydraulic System Components ......................................5-7
KEY TO FIGURE 2 ......................................................................................5-8
Figure 2 - Main Hydraulic System............................................................5-9
AUXILIARY SYSTEM ...................................................................................5-10
Figure 3 - Auxiliary Hydraulic System Components...............................5-10
Figure 4 - Auxiliary Hydraulic System ....................................................5-11
CONTROLS and INDICATIONS ................................................................5-12
FLUID STORAGE ......................................................................................5-12
OPERATION ..............................................................................................5-12
Figure 5 - Operation of Auxiliary Hydraulic System Selector Handle.....5-13
RESETTING THE MAIN SYSTEM.............................................................5-14

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Section III - SYSTEMS DESCRIPTION

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Page 5-2 Sub-section 5 Pilot’s Operating Manual

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Section III - SYSTEMS DESCRIPTION
GENERAL

Hydraulic power is provided by independent Main and Auxiliary systems for operation of the following
services:

MAIN HYDRAULIC SYSTEM

• Normal extension and retraction of the landing gear

• Normal and emergency operation of the wheel brakes

• Nosewheel steering

• Normal operation of the flaps

• Operation of the airbrakes

• Stall identification (stick push)

• Operation of the thrust reversers

AUXILIARY HYDRAULIC SYSTEM

• Emergency extension of the landing gear

• Emergency operation of the flaps

This Sub-section only covers the generation of hydraulic power.

Refer to the following Sub-sections for details of the hydraulic services:

• Sub-section 2 ENGINES (for thrust reversers)

• Sub-section 6 FLIGHT CONTROLS (Flaps, Airbrakes and Stall identification)

• Sub-section 8 LANDING GEAR (also wheel brakes and nosewheel steering)

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Section III - SYSTEMS DESCRIPTION
MAIN SYSTEM

Table 1: Indicators and Annunciators

Item Location Parameter

psi
Combined BRAKES (2)
Center instrument panel Brakes: 2000
and SUPPLY indicator
Supply: 3000

HYD OVHT Main MWS panel Hydraulic fluid overheat warning 90° C

HYD 1 Main supply low pressure warning

Main MWS panel
LO PRESS ≤1500 psi

EMRG BRK Emergency brakes accumulator low

Main MWS panel
LO PRESS pressure warning ≤ 2250 psi

Accumulator pressure
indicators Rear equipment bay Initial charge at 1000 psi
(main and wheel brakes)
Accumulator pressure
Rear equipment bay Initial charge at 1500 psi
indicators (thrust reversers)
Main reservoir contents level Parameters stated on label next to
Rear equipment bay
tube reservoir
Main reservoir air pressure
Rear equipment bay 0 to 30 psi is normal
gauge

FLUID STORAGE
System fluid is stored in a spherical shaped reservoir located in the rear equipment bay. Fluid contents
are displayed in a level indicator tube, integral with the reservoir.

Air, tapped from both engines is used to pressurize the reservoir to make sure a supply is fed to the
pumps under all flight conditions.

The air is supplied to the reservoir via check valves and a pressure reducing valve.

The reservoir has an inward and outward relief valve as well as a pressure gauge.

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Section III - SYSTEMS DESCRIPTION
POWER GENERATION
Fluid is supplied from the reservoir through a suction filter to the two variable-delivery engine driven
pumps, one per engine.

An on/off valve in each suction line is interconnected to the related HP cock lever. Isolation of the
hydraulic fluid supply is therefore simultaneous with engine shut-down. When an on/off valve is closed,
a closed-circuit via the valve provides a full volume supply to the pump for lubrication.

Each pump delivers fluid at a nominal pressure of 3000 psi via a low pressure switch, snubber and
check valve, to the pressure filter in the main delivery line to the airplane systems.

A capacitor is installed in the delivery line from the No. 1 pump.

High Pressure Relief

Two full-flow relief valves are located in tappings off the delivery line from each pump and are provided
to limit the maximum pump pressure in the event of the failure of the pump pressure control.

Should the pump delivery pressure rise above 3750 psi, the relief valve operates to pass fluid into the
return line.

Low Pressure Indication

The low pressure switch operates if the pump pressure falls to 1500 psi. A time delay prevents the
associated HYD # LO PRESS annunciator illuminating until the timed period has elapsed. This prevents
a spurious annunciation due to temporary low pressure conditions caused by system fluctuations. Once
the annunciation is illuminated, it remains so until the pressure rises above 1850 psi.

Hand Pump
The Main system can be pressurized for ground servicing purposes by a hand pump located in the rear
equipment bay. The hand pump inlet is connected to the line from the suction filter. When operated, the
pump passes pressurized fluid through a check valve, into the main system.

MAINTAINED PRESSURE PATHS

Fluid passes through a Pressure Maintaining Valve (PMV) to the normal wheel brake and stall
identification paths.

The PMV shuts off if the pressure upstream of it falls to 2300 psi. This makes sure the pressure in the
main accumulator is sufficient for several operations of the stall identification system and operation of
the normal wheel brakes when landing.

Thrust Reversers
Fluid stored in the thrust reverser accumulator is prevented from leaking back to the main system by a
check valve.

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Section III - SYSTEMS DESCRIPTION
Wheel Brakes Emergency Path
Main system pressure is distributed through a check valve to the emergency brake accumulator and
the emergency brake reducing valve.

Should the main system pressure fail, the check valve retains the pressure stored in the emergency
brakes accumulator. For details of the number of brake applications available using the fluid from the
accumulator, refer to Sub-section 8 LANDING GEAR.

Low pressure (below 2250 psi) in the path or accumulator is indicated by the illumination of the EMRG
BRK LO PRESS annunciator on the main MWS panel.

Accumulators
Three piston-type accumulators, each installed with a pressure indicator and a gas charging valve, are
located in the rear equipment bay. The piston separates charges of gas from the hydraulic fluid.

With no hydraulic pressure in the system, the main system and the emergency brake accumulators are
initially charged with nitrogen at 1000 psi.

The initial charge for the thrust reverser accumulator is 1500 psi.

NON-MAINTAINED PRESSURE PATHS

The landing gear, flaps, airbrakes and nose wheel steering paths are directly fed with system pressure
with no provision to cover delivery pressure failure.

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Section III - SYSTEMS DESCRIPTION

ISOLATION VALVE

STALL IDENT UNIT

ISOLATION VALVE

AIR BRAKE
ACTUATOR

AIR BRAKE
ACTUATOR

Figure 1
Main Hydraulic System Components

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Section III - SYSTEMS DESCRIPTION

KEY TO FIGURE 2

Component Identification Pipeline Colors

1. Capacitor Air ......................................

2. Pressure switch and snubber Suction ..............................

3. Full flow relief valves Pressure ............................

4. Ground servicing hand pump Return ...............................

5. Emergency brakes reducing valve Emergency Brakes ............

6. Normal brakes reducing valve Maintained Pressure .........

7. Pressure transmitter

8. Thrust reverser release valve

9. Pressure relief valve, thrust reverser

and nose wheel steering

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Section III - SYSTEMS DESCRIPTION

No. 1 ENGINE PRESSURE

BLEED AIR No. 2 ENGINE PRESSURE GAUGE
BLEED AIR REDUCING
VALVE MAIN
RESERVOIR
GROUND AIR
SUCTION
CONNECTION FILTER
HYD OVHT
No. 1 HP No. 2 HP TEMP
COCK COCK SWITCH

ON/OFF ON/OFF
VALVE VALVE
lubrication loop
EDP EDP (when HP cock
is closed)

1
HYD 1
3 3 HYD 2
LO PRESS LO PRESS
2 2
8
PRESSURE THRUST 9
FILTER REVERSER
ACCUMULATOR
THRUST
4 REVERSERS

LANDING
GEAR

EMRG BRK PRESS.

LO PRESS PMV FLAPS
SWITCH

AIRBRAKES

NOSE WHEEL 9
STEERING
EMERGENCY BRAKE
ACCUMULATOR

SPEED
7 CONTROL
RESTRICTOR
5 6
STALL IDENT’N
SYSTEM (STICK PUSH)
BRAKE PRESSURE
CONTROL GAUGE
VALVE
MAIN
ACCUMULATOR

TO BRAKE UNITS

Figure 2
Main Hydraulic System

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Section III - SYSTEMS DESCRIPTION
AUXILIARY SYSTEM

The auxiliary hydraulic system provides an alternative source of hydraulic power for landing gear
lowering and flaps operation. The system is hand-operated, and when selected, is independent of the
main system.

The following notes must be observed:

NOTES:
1. Emergency lowering of the landing gear is available regardless of the setting of the
landing gear selector lever but the flaps must be selected to the required setting.
2. When using the auxiliary system, lowering of the landing gear always occurs before
operation of the flaps.
3. The system cannot be used to raise the landing gear.
4. Following the selection of the auxiliary system, it must be reset manually before the
main system can be used to operate the landing gear.
CAUTION: IF A SELECTION OF THE AUXILIARY SYSTEM HAS BEEN MADE FOLLOWING A MAIN
SYSTEM FAILURE, THE AUXILIARY SYSTEM MUST NOT BE RESET IN FLIGHT. IGNORING
THIS CAUTION COULD RESULT IN THE LANDING GEAR COLLAPSING ON TOUCHDOWN.

Figure 3
Auxiliary Hydraulic System Components

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Section III - SYSTEMS DESCRIPTION

MWS PANEL

AUX HYD LANDING

LO LEVEL GEAR
ON/OFF VALVE SELECTOR

LEVEL DUMP
INDICATOR
VALVE

RESERVOIR

FILTER
FLAP CONTROL
UNIT
MAIN
SYSTEM
SHUTTLE
VALVE

NOSE
GEAR
ACTUATOR

KEY

AUXILIARY
SYSTEM
SHUTTLE
VALVES
MAIN
SYSTEM
SUCTION
MAIN
RETURN GEAR
ACTUATORS

CIRCUIT SHOWN WITH SELECTOR HANDLE PULLED

Figure 4
Auxiliary Hydraulic System

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Section III - SYSTEMS DESCRIPTION
CONTROLS and INDICATIONS

CONTROL LOCATION
Left side of center instrument panel,
AUX HYD SYSTEM PULL selector handle
adjacent to FMS No. 1 display
EMERG HYD PUMP operating handle socket Pilot’s floorboard, adjacent to the center pedestal
AUX HYD LO LEVEL annunciator MWS main panel
Auxiliary reservoir contents level indicator tube Visible from nose gear bay

FLUID STORAGE
The fluid supply for the auxiliary system is contained in a 6.01 U.S. pints (2.84 liter) reservoir located
adjacent to the nose gear bay.

A float switch in the reservoir is connected to an AUX HYD LO LEVEL annunciator. The annunciator
will illuminate when approximately 0.6 U.S. pint (0.28 liter) of fluid has been drawn out of the reservoir.

A full reservoir provides sufficient fluid for at least one emergency lowering of the landing gear, and
followed by at least one extension of the flaps to the landing position.

OPERATION
Selection of the auxiliary system is by pulling the red-handled AUX HYD SYSTEM PULL selector
handle.

Prior to selection, the system valves are set for normal main hydraulic system operation, i.e:

• On/off valve - open to relieve fluid seepage from the Auxiliary system.

• Dump valve - set to connect Main system pressure and system return to the main and nose gear
lines.

• Shuttle valves - With no pressure in the auxiliary system, the shuttle valves close the auxiliary
system supply ports on the landing gear jacks, allowing main system pressure to operate the
jacks.

With the lever in the normal position, a baulk prevents operation of the auxiliary system hand pump.
The system is prepared for use by first inserting the rudder gust lock handle into the AUX HYD SYSTEM
hand pump socket and then firmly pulling the red-handled PULL handle. This action operates the
system valves as follows:

• On/off valve - closed to prevent the auxiliary system fluid passing to the return line.

• Dump valve - set to cut-off the main system pressure and remove any main system pressure in
the landing gear path by interconnecting the normal up and down lines of the main and nose gear
jacks to the return line.

Pulling the control lever also releases the baulk and permits operation of the hand pump. The control
lever is held in the selected position by a spring unit.

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Section III - SYSTEMS DESCRIPTION
Manual operation of the hand pump draws fluid from the auxiliary reservoir. The fluid is delivered via
the check valve and the shuttle valves to the down side of the main and nose gear jacks. Fluid from the
check valve is also delivered to the flap control unit.

NOTE: Shortly after the commencement of emergency lowering, hand pump resistance decreases
(when the gear uplocks release) and the AUX HYD LO LEVEL annunciator is illuminated.

Continued operation of the hand pump locks the gear down.

CAUTION: WHEN OPERATING THE AUXILIARY HYDRAULIC SYSTEM TO LOWER

THE LANDING GEAR, THE HAND PUMP ACTION MUST BE CONTINUED,
AFTER 3 GREENS ARE ACHIEVED, UNTIL POSITIVE RESISTANCE IS
FELT TO MAKE SURE THE LANDING GEAR IS DOWN AND LOCKED.

Selection of the flaps and operation of the hand pump will move the flaps to the required position.

Figure 5
Operation of Auxiliary Hydraulic System Selector Handle

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Section III - SYSTEMS DESCRIPTION
RESETTING THE MAIN SYSTEM
Following use of the auxiliary system, the main system must be reset before normal operation of the
landing gear.

NOTES:
1. With the main system pressurized normally, the setting of the AUX HYD SYSTEM PULL
control lever has no effect on flaps operation.
2. If a selection is made to demonstrate or exercise the auxiliary system, operation of the
flaps will be from the main system.
To reset the system, first make sure the LANDING GEAR selector lever is in the down position, then
push the AUX HYD SYSTEM PULL lever fully in. This action opens the on/off valve to vent fluid
pressure in the auxiliary system lines to the return. The shuttle valves move back to connect the main
system to the down side of the gear jacks.

With the on/off valve open the check valve prevents normal pressure from the main system return line
draining the auxiliary reservoir and the baulk is repositioned by the spring unit to prevent movement of
the hand pump socket.

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