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Single Aisle TECHNICAL TRAINING MANUAL

T1+T2 (CFM 56 / ME) (Lvl 2&3)

APU

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This document must be used for training purposes only

Under no circumstances should this document be used as a reference

It will not be updated.

All rights reserved

No part of this manual may be reproduced in any form,

by photostat, microfilm, retrieval system, or any other means,

without the prior written permission of AIRBUS S.A.S.

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APU

GENERAL

APU Level 2 (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

APU Installation Presentation (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18APU Fuel Feed System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

HONEYWELL 131-9(A)

APU Drain System Presentation (2) . . . . . . . . . . . . . . . . . . . . . . . . . . 22

APU Basic Description (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

APU Ignition & Starting D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

APU Fuel System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

APU Oil System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

APU Air System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

APU System Management D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . 40APU Warnings (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

ECB Interfaces (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

HONEYWELL GTCP 36-300

APU Drain System Presentation (2) . . . . . . . . . . . . . . . . . . . . . . . . . . 72

APU Basic Description (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

APU Ignition & Starting D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

APU Fuel System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

APU Oil System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

APU Air System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

APU System Management D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . 90# APU Warnings (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

ECB Interfaces (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

APU Film Presentation (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

APIC

APU Drain System Presentation (2) . . . . . . . . . . . . . . . . . . . . . . . . . 140

APU Basic Description (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

APU Ignition & Starting D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

APU Fuel System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

APU Oil System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

APU Air System D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

APU System Management D/O (3) . . . . . . . . . . . . . . . . . . . . . . . . . 158# APU Warnings (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

ECB Interfaces (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

APU Film Presentation (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

MAINTENANCE PRACTICE

COMPT Access Doors Opening & Closing (2) . . . . . . . . . . . . . . . . 214

APU Removal / Installation (3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

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APU LEVEL 2 (2)

SYSTEM OVERVIEW

The Auxiliary Power Unit (APU) is a constant speed gas turbine engine.

It is located in the unpressurized tail cone. The APU is a self-contained

unit, which enables the aircraft to be independent of external pneumatic

and electrical power sources.

The constant-speed gas turbine engine drives the accessory gearbox and

a load compressor. The APU provides:

- electrical power for the aircraft systems,

- bleed air for engine starting (MES), air conditioning (ECS) and wing

anti ice testing on ground (not GTCP 36-300),

- bleed air for air conditioning and pressurization in flight until the

specified manufacturer limit.

The APU is designed to operate throughout the entire flight envelope.Electrical power is available whenever the APU operates, but bleed air

is shut off above the specified manufacturer limit.

The APU has an air intake flap. The intake flap is open when the APU

master switch is selected ON and closes when the master switch is selected

OFF. When open, it provides air to the APU inlet for combustion and

pneumatic supply.

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SYSTEM OVERVIEW

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APU LEVEL 2 (2)

SERVICING

APU OIL SERVICING

APU oil servicing is accomplished on an "as-needed" basis or after

scheduled oil quantity checks. The oil indicating system shows if the

oil quantity is sufficient or if an oil servicing is necessary.

The oil level information is displayed on the EIS and the Multipurpose

Control & Display Units (MCDUs) in the cockpit on:

- the APU page on the lower ECAM display unit (LOW OIL LEVEL

advisory),

- the APU SERVICE DATA page on the MCDU, indicating APU

OIL Level O.K. or LOW.

NOTE: Note: The advisory appears on the ECAM APU page whenthe oil level has reached the ADD mark on the APU oil tank.

Airbus recommends servicing the APU oil at the next daily

maintenance when the LOW OIL LEVEL message comes on. With

no oil leakage, sufficient oil is available to allow a further 10 hours

of APU operation.

Prior to servicing, shut down the APU and open the APU cowl doors.

Make sure to use the operator approved oil for servicing (operators

may select from the approved list). The oil may be serviced by the

gravity (most common) or pressure fill procedure (optional).

Gravity procedure:

- Open the lock and slowly loosen the oil filler cap to release remaining

pressure from the oil reservoir,

- Check sight glass for level,

- Slowly add oil until the level is at the FULL mark on the sight glass.

Pressure fill procedure:

- Check sight glass for level,

- Connect pressure and overfill lines to APU gearbox,

- Slowly pump oil into the gearbox until the level is at the FULL mark

on the sight glass.

Close and lock the oil filler cap.

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SERVICING - APU OIL SERVICING

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APU LEVEL 2 (2)

SERVICING (continued)

APU COWL DOOR OPENING & CLOSING

The APU cowl doors are secured with three quick-release fasteners

and four shoot bolts. The quick-release fasteners secure the doors

together and the shoot bolts secure the doors to the aircraft structure.

Procedure to open the doors:

- Release the quick-release fasteners,

- Hold the LH door and release the latches of the 2 shoot bolts,

- Open the door and secure it with the telescopic strut,

- Hold the RH door and release the latches of the 2 shoot bolts,

- Open the door and use the control handle to secure the door over

center.

The doors are closed opposite from the opening sequence. The RHdoor is closed and secured first.

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SERVICING - APU COWL DOOR OPENING & CLOSING

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APU LEVEL 2 (2)

MEL/DEACTIVATION

In case of an APU inlet actuator failure, the APU may be dispatched per

MEL with the inlet OPEN or CLOSED. The APU will only be operational

with the inlet deactivated OPEN (for a maximum of 10 days).

The air inlet actuator is equipped with a manual drive. In case of failure

the manual drive may be used to move the inlet to the required position

prior to deactivation. There are 2 different actuators that may be installed.

One requires 47 turns of the manual drive for one full travel of the inlet.

The other requires 87 turns. Access to the actuator is through an access

door near the APU inlet on the right hand side of the fuselage.

Deactivation procedure:

- get access to the actuator,

- disconnect the actuator electrical connector from the fixed connectoron the frame and install a blanking cap,

- use the manual drive to move the inlet to the required position. Use a

torque wrench to avoid damaging the actuator.

If the inlet is deactivated CLOSED, no further action is needed other than

to placard the APU inoperative. If the inlet is deactivated OPEN, the

following procedure has to be accomplished.

When the inlet is in the OPEN position, a jumper lead needs to be installed

to close the circuit and allow the APU to start. Make a dummy connector

and paint it red for easy identification.

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MEL/DEACTIVATION

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MEL/DEACTIVATION

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APU LEVEL 2 (2)

MAINTENANCE TIPS

The APU fuel supply line is equipped with a drain and vent valve which

enables the line to be purged of air after maintenance. The drain valve islocated in the APU compartment in the fuel supply line to the fuel control.

A switch labeled FUEL VENT PUSH is installed on the APU

compartment forward firewall to allow maintenance to operate the APU

fuel pump and purge the fuel line from the APU compartment. This switch

allows the APU pump to operate and the APU Low Pressure fuel valve

to open without the APU Master Switch ON.

A drain valve adapter tool is connected to the drain valve.

On the front firewall of the APU compartment:

- Push and hold the FUEL VENT pushbutton switch. At the APU fuel

vent and drain valve, a continuous flow of fuel indicates that the APUfuel pump is operating and the line is purged,

- Release the FUEL VENT pushbutton switch. The flow of fuel stops

when the APU fuel pump stops running,

- Disconnect the adapter tool.

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MAINTENANCE TIPS

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APU LEVEL 2 (2)

MAINTENANCE TIPS (continued)

APU OPERATION WITH COWL DOORS OPEN

If it is necessary to operate the APU for maintenance with the cowls

open, be sure to:

- Make sure the doors are secured in the Open position,

- Be aware of suction at inlet. Small items could be ingested,

- Make sure that proper fire-fighting equipment is available.

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MAINTENANCE TIPS - APU OPERATION WITH COWL DOORS OPEN

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APU LEVEL 2 (2)

ENVIRONMENTAL PRECAUTIONS

Do not discharge products such as oil, fuel, solvent, lubricant either in

trash bins, soil or into the water network (drains, gutters, rain water, wastewater, etc...).

Sort waste fluids and use specific waste disposal containers.

Each product must be stored in an appropriate and specific cabinet or

room such as a fire-resistant and sealed cupboard.

Avoid use of the APU if APU BLEED air is not necessary. Turn-off

unused ground service equipment (GPU, Air conditioning cart, etc...) if

no work is being done or nobody is present on the aircraft.

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ENVIRONMENTAL PRECAUTIONS

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APU INSTALLATION PRESENTATION (2)

GENERAL

The Auxiliary Power Unit (APU) is installed in a fireproof COMParTment

(COMPT) located in the fuselage tail cone.

MOUNTS

Seven tie rods attach the APU to the structure brackets on the APU

COMPT ceiling. These tie rods also connect to the APU three-point

mounted suspension system. Vibration isolators are installed between

the APU mount brackets and the tie rods to reduce the transmission of

A/C vibrations and shocks to the APU. The isolators also prevent the

transmission of vibrations from the APU to the A/C structure.

AIR INTAKE FLAP

The air intake system ducts ambient air to the APU plenum chamber. An

air intake flap cuts off the air supply when the APU does not operate. In

case of failure, the air intake flap can be opened or closed manually by

a manual override device.

AIR INTAKE DUCT

The air intake duct, which is composed of a diffuser and elbow, provides

correct airflow to the APU plenum. The air intake duct is attached to the

right access door.

EXHAUST

The exhaust system lets the APU exhaust gas flow into the atmosphere

and muffles the noise from the exhaust. The exhaust muffler thermal

insulation protects the A/C structure.

ACCESS DOORS

Two access doors allow access to the APU COMPT. The access doors

on the bottom of the tail cone open outwards to allow the APU to beinspected, lifted and lowered.

DRAIN SYSTEM

A drain system prevents the collection of fluids in the APU COMPT.

Any fluid that may accumulate in the APU COMPT is delivered to a

drain mast. Some of the fluids are collected in a drain tank in the APU

COMPT, which is emptied through the drain mast when the A/C is above

200 kt.

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GENERAL ... DRAIN SYSTEM

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APU FUEL FEED SYSTEM D/O (3)

GENERAL

The Auxiliary Power Unit (APU) fuel feed system is used to provide fuel

necessary for correct APU operation. This system is composed of:- fuel pump (115V AC, 400Hz, single phase),

- LP valve,

- APU inlet LP switch,

- fuel drain and vent system.

FUEL PUMP

The APU fuel pump is a centrifugal pump driven by a single phase AC

motor. This pump is controlled to run if the APU MASTER SW P/B is

set to ON and the fuel crossfeed line pressure is not sufficient. The fuel

crossfeed line pressure switch controls the operation of the APU fuelpump. The APU fuel pump runs as soon as the pump inlet pressure is

lower than 21.8 psi (1.50 bar). It stops when the pressure is above 23.2

psi (1.60 bar).

FUEL LP VALVE

Two DC motors drive the APU fuel LP valve. This valve is open as long

as the Electronic Control Box (ECB) is powered. When closed, it prevents

pressurization of the APU fuel feed line and flow of fuel into a specific

fire zone. The APU fuel LP valve is automatically closed when:

- the APU MASTER SW P/B has been released out and before ECB isdeenergized,

- the ECB commands a protective shut down in case of abnormal APU

parameters,

- the ECB commands an emergency shut down in case of APU fire or

overheat detection,

- the APU FIRE P/B is released out in the cockpit,

- the APU SHUT OFF P/B has been pressed on the external power control

panel.

APU INLET LP SWITCH

At the inlet connection of the Fuel Control Unit (FCU), a pressure switch

transmits LP information through the ECB to the APU ECAM page. TheFUEL LOw PRessure message is displayed on the APU ECAM page if:

- the APU speed is greater than 7% rpm and the APU is supposed to run,

- the fuel pressure is lower than 15.8 psi (1.01 bar).

The ECB memorizes this information in its BITE memory even if the

pressure increases above 17.3 psi (1.19 bar).

FUEL DRAIN AND VENT SYSTEM

A vent APU fuel line P/B, located on the front firewall allows the APU

fuel feed line to be purged during ground maintenance. As long as the

P/B is held pressed in, the APU fuel LP isolation valve is open and theAPU fuel pump runs. A fuel drain and vent valve is installed in the APU

compartment at the fuel inlet connection to the FCU. It allows fuel to be

drained and air to be bled.

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GENERAL ... FUEL DRAIN AND VENT SYSTEM

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APU DRAIN SYSTEM PRESENTATION (2)

APU DRAIN SYSTEM

A drain system prevents the collection of fluids in the Auxiliary Power

Unit (APU) system and compartment.

FUEL CONTROL UNIT/OIL PUMP SEAL DRAIN

The fuel and oil pump seal drain line is routed via a collector line to the

drain tank. This line drains fuel or oil leaks.

INLET GUIDE VANE ACTUATOR DRAIN

The Inlet Guide Vane (IGV) actuator drain line is routed via the collector

line to the drain tank. This line drains only fuel leaks.

GEARBOX VENT

The oil reservoir has a connection to the ambient air through an air/oil

separator. The gear driven air/oil separator is connected through a gearbox

vent line to the APU exhaust cone.

SURGE CONTROL VALVE DRAIN

The surge control valve fuel is drained into the drain tank by the Fuel

Control Unit (FCU)/IGV actuator common drain line.

LOAD COMPRESSOR CAVITY DRAINTo prevent any ingestion of oil in the bleed system the load compressor

bearing cavities are kept dry by buffering air into the main shaft seals.

An oil leak witness drain is located aft of the seal to collect any oil

leakage. The oil is drained directly overboard through the drain mast.

TURBINE PLENUM DRAIN

A turbine plenum drain orifice is provided to drain fuel that may

accumulate in the combustor following an unsuccessful light-up. Thefuel is drained directly overboard through the drain mast.

EXHAUST MUFFLER DRAIN

The exhaust muffler drain line is routed to the drain mast. This drain line

collects water or cleaning fluid.

APU COMPARTMENT DRAIN

Water coming from rain or condensate humidity, cleaning agents and

any oil and fuel in the compartment, due to leaks or APU servicing, are

drained to the lowest point of the APU door and through the drain mast

overboard.

DRAIN TANK

For venting and evacuation, the drain tank is connected to the drain mast.

Airflow across the drain mast creates a vacuum in the drain line. The

suction effect produced at 200 kts, is sufficient to remove the contents

of the drain tank. A vent line ventilates the drain tank and drain lines.

The APU drain lines are connected to the right access door drain lines

through spring adapter kiss seals.

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APU DRAIN SYSTEM ... DRAIN TANK

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APU BASIC DESCRIPTION (3)

GENERAL

The Auxiliary Power Unit (APU) is of a modular design. The three APU

modules are:- the power section,

- the load compressor,

- the accessory drive gearbox.

ENGINE COMPRESSOR

The compressor is of a single stage centrifugal compressor design. The

main components of the compressor are:

- a single stage centrifugal impeller,

- single stage diffuser vanes,

- axial de-swirl vanes.

COMBUSTION CHAMBER

The combustion chamber is of a reverse flow annular design and is

installed inside the turbine plenum. The main parts of the combustion

chamber are:

- the inner combustion chamber shell,

- the outer combustion chamber shell.

The following components are installed on the combustion chamber:

- an igniter plug,

- 10 dual orifice fuel nozzles.

TURBINE

The turbine assembly drives the engine compressor, the load compressor

and the gear train of the Accessory Gearbox (AGB). The two-stage axial

flow turbine includes:

- a cooled first stage nozzle,

- inserted first stage rotor blades,

- an un cooled second stage stator,

- a dual alloy second stage rotor,

- an annular exhaust diffuser.

LOAD COMPRESSOR

The load compressor is of a single stage centrifugal design. It supplies

bleed air to the pneumatic system. The main components of the load

compressor are:

- the inlet guide vane assembly,

- the load compressor impeller,

- the load compressor diffuser,

- the load compressor scroll.

INLET GUIDE VANES

The Inlet Guide Vanes (IGVs) control the amount of bleed air flow andpressure from the APU load compressor. The 16 IGVs are moved

simultaneously by a gear train operated by an actuator. The IGV actuator

is operated by high-pressure fuel supplied from the Fuel Control Unit

(FCU). The IGV opening angle depends on the bleed air demand for:

- Main Engine Start (MES) system,

- Environmental Control System (ECS).

ACCESSORY GEARBOX

The gearbox transmits the shaft power to the APU accessories and to the

APU generator, which are installed on the gearbox pads. The gearbox isalso the oil reservoir for the APU lubrication system. The components

mounted on the accessory gearbox are:

- the starter motor assembly,

- the cooling air fan assembly,

- the lubrication unit with the oil pump assembly which drives the FCU,

- the AC generator.

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GENERAL ... ACCESSORY GEARBOX

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APU IGNITION & STARTING D/O (3)

STARTER CONTROL

During starting, the electrical starter causes initial rotation of the Auxiliary

Power Unit (APU) shaft when it drives the Accessory Gearbox (AGB).When the APU speed is around 50%, the Electronic Control Box (ECB)

stops the electrical supply to the starter by opening the main start

contactor.

IGNITION CONTROL

The ignition system causes initial light-off of the fuel air mixture. The

ignition system includes an ignition box that energizes an igniter plug.

During starting, the ECB switches the ignition to ON between 7% and

60%. When the APU speed drops below 95% due to a flame-out, the

ECB starts the ignition until the APU reaches again 100% of speed.

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STARTER CONTROL & IGNITION CONTROL

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APU FUEL SYSTEM D/O (3)

GENERAL

The fuel system supplies metered fuel to sustain combustion. Part of the

fuel, as muscle pressure, operates the Inlet Guide Vane (IGV) actuatorand the surge control valve actuator. This system is made of:

- Fuel Control Unit (FCU),

- fuel schedule,

- muscle pressure,

- fuel shut-off,

- flow divider and solenoid valve,

- fuel supply,

- fuel drain,

- control,

- monitoring.

FUEL CONTROL UNIT

The FCU has six functions:

- fuel filtering,

- pressure increase,

- fuel metering,

- flow meter control,

- positive fuel shut-off,

- fuel muscle pressure regulation.

The FCU is made of a LP inlet fuel filter, a High Pressure (HP) fuel

pump, a pump relief valve, a HP fuel filter, an actuator pressure regulator

for hydraulic fuel operation, a torque-motor metering valve, a resistive

temperature device, a delta pressure regulator, a flow-meter pressurizing

valve, a fuel-shutoff solenoid valve.

FUEL SCHEDULE

The Electronic Control Box (ECB) controls the fuel-metering valve

through a torque motor.

The ECB:

- schedules fuel flow during start sequence, on-speed operation and

shutdown sequence,

- refers to information on the flowmeter pressurizing valve to correct fuelflow and in relation to the fuel temperature (resistive-temperature device

signal),

- modulates the on-speed fuel schedule to agree with the aircraft demand

for bleed air and electrical power.

MUSCLE PRESSURE

Additionally fuel muscle pressure 250 psig operates the surge control

valve actuator for air release to the exhaust and the load-compressor IGV

actuator. Servo fuel return goes back to the pump inlet.

FUEL SHUT-OFF

The ECB controls the fuel 3-way solenoid valve for positive fuel shut-off.

The valve is controlled open during the start sequence and closed during

the stop sequence. Fuel goes back to the pump inlet.

FLOW DIVIDER AND SOLENOID VALVE

The flow divider supplies fuel in sequence to the primary and secondary

manifolds. It has a usually open fuel solenoid and a check valve. During

cold start or high altitude operation, the ECB energizes the solenoid valve

to close during the first 30% speed of the Auxiliary Power Unit (APU)and all fuel flow is pushed through the primary nozzles for better engine

acceleration.

FUEL SUPPLY

Two fuel manifolds and 10 dual fuel-nozzles supply fuel. Each fuel-nozzle

has a primary and a secondary fuel orifice. When APU start is selected,

the primary fuel orifice is supplied and when the fuel pressure is more

than 125 psig the check valve in the flow divider assembly opens to

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supply the secondary fuel orifice. During on-speed operation, the two

orifices are supplied.

FUEL DRAIN

Drain lines are connected to the FCU seal drain, IGV actuator and surgecontrol valve are routed to one single drain connection, on the APU drain

bracket (FWD R/H side of APU).

CONTROL

The ECB controls the fuel system with several parameters. During

on-speed operation, the ECB uses APU speed, Exhaust Gas Temperature

(EGT) and aircraft demand signals. During start, it uses speed, EGT, air

inlet pressure and temperature sensors (P2 and T2). The ECB operates

the fuel metering valve, the flow divider solenoid valve and fuel shut-off

3-way solenoid valve.

MONITORING

Fuel filter replacement is recommended every 8500 Flight Hours.

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GENERAL ... MONITORING

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APU OIL SYSTEM D/O (3)

GENERAL

The oil system of the Auxiliary Power Unit (APU) lubricates and

decreases the temperature of the power section, load compressor, gearboxand AC generator.

This system is made of:

- storage,

- supply,

- scavenge,

- venting,

- control,

- protection,

- monitoring.

STORAGE

The sump of the APU Accessory Gearbox (AGB) is the oil reservoir.

The AGB sump contains 6.26 l (1.65 US gal) of oil. The oil reservoir can

be filled by gravity or by pressure.

The AGB has:

- an oil fill cap for gravity filling,

- optional pressure oil servicing with a pressure fill and overfill port,

- an oil-level sight glass with FULL and ADD marks,

- a magnetic chip detector and oil drain plug installed at the lowest point

of the AGB,

- an oil heater.

SUPPLY

A three-element gerotor pressure pump pulls the oil from the sump. A

pressure-regulating valve and ultimate-relief valve assembly keeps a

constant lube supply pressure for oil supply to the engine and generator

and prevents over-pressurization of the lube system. Pressure-regulated

oil goes through a cooler and a disposable filter. The bypass valve opens

at an oil temperature below 60°C (140 °F) or when there is a differential

pressure between 55 - 60 psi around the oil cooler. The oil is then sent

to the cooling fan splines, the APU spline shaft, the APU supporting

bearings rear and front, the gearbox pinions and the electrical AC

generator.

SCAVENGE

A three-element gerotor scavenge pump and a filter sends oil from the

electrical generator to the sump. The oil from the bearing cavity of the

APU turbine goes back to the sump through a single-element gerotor

scavenge pump. Oil from the gearbox pinions and the APU front bearing

is scavenged by gravity.

VENTING

The oil from the generator is sent against the gearbox wall; this removes

the air, that is mixed with the oil. An air/oil separator removes the oil

particles from the gearbox air. This oil-free air is released in the APU

exhaust.

CONTROL

The Electronic Control Box (ECB) only controls the de-oiling valve in

the oil system. The de-oiling solenoid valve is electrically opened during

APU start to make sure of cold start conditions and to decrease the load

on the pressure pump. The solenoid valve is open during start-up to 60%RPM when:

- the oil sump temperature is below -6.7°C (+20°F),

- or the A/C altitude is above 20,000 ft,

- or the APU fuel temperature is below -12.2°C (+10°F).

The valve is energized open during every APU shutdown between 50%

and 7% speed.

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PROTECTION

The ECB gives protection to the APU if there is an oil system malfunction.

The ECB monitors oil pressure and oil temperature. If one of the oil

parameters is out of limit, the ECB starts an automatic APU shutdown

without time delay:- gearbox high oil temp threshold: 162.78°C (325°F),

- oil LP: 33 psi.

The ECB also stops the APU if a delta pressure switch at the scavenge

filter or at the lubrication filter shows impending filter clogging.

MONITORING

The oil system is monitored to increase the APU life. The oil sump is

installed with a low-level switch to show maintenance information in the

cockpit. When the level is at the "ADD" mark 4.60 l (1.22 US gal), the

APU can continue to operate for 10 hours maximun. This changes withthe different operating attitudes of the A/C in flight. A magnetic drain

plug, put fully in the APU oil, lets the oil drain from the sump and attracts

ferrous metal particles.

OIL HEATER

The control of the oil heater is independent of the ECB. When the oil

temperature is below 16 °C (61 °F) and the APU master switch is released

out, the heater is supplied with 115VAC.

The oil heater is switched off when the oil temperature increases above

49°C (120 °F) or the master switch is selected ON.

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GENERAL ... OIL HEATER

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APU AIR SYSTEM D/O (3)

GENERAL

The Auxiliary Power Unit (APU) load compressor supplies the APU

bleed air. The quantity changes with the different bleed air demands of the pneumatic system. This system is made up of:

- bleed supply,

- bleed control,

- surge protection,

- oil cooling,

- compartment cooling,

- oil vent,

- control,

- monitoring.

BLEED SUPPLY

Bleed air supply to the A/C pneumatic system is controlled by a load

control valve. The pneumatically-actuated CLOSE/OPEN butterfly valve,

which allows or stops the bleed airflow from the APU to the A/C users,

is controlled by the Electronic Control Box (ECB) and opens when the

APU BLEED P/BSW is set to the ON position.

BLEED CONTROL

The amount of air required by the pneumatic system and delivered by

the APU load compressor is controlled by the load compressor Inlet GuideVanes (IGVs). The IGVs are moved by a fuel-powered actuator.

SURGE PROTECTION

Load compressor surge protection is ensured by a surge control valve,

which discharges the excess of air in the exhaust. The surge control valve

is hydraulically operated for accurate and fast operation. The hydraulic

fluid is high pressure fuel from the Fuel Control Unit (FCU) 250 to 300

psig.

OIL COOLING

A gearbox-driven fan draws air from the inlet plenum and forces it to

pass through the oil cooler. After leaving the oil cooler, the air isdischarged overboard.

COMPARTMENT COOLING

Air supplied by the fan, driven by one of the gears of the gearbox, is also

used for APU compartment cooling. Cooling air flows through the outlets

located on the cooling fan outlet duct. Natural convection ventilates the

APU compartment through a vent grill in the upper left area of the

compartment when the APU is not in operation.

OIL VENTThe gearbox is vented to the APU exhaust. The air is bled after an air/oil

separator action.

CONTROL

The ECB controls the air system using several parameters from the

following components installed on the APU:

- APU inlet pressure (P2) and temperature (T2) sensors,

- load compressor discharge pressure sensor (PT) and differential pressure

sensor (DP),

- command and feedback signals from the actuators and the valves (IGVactuator, Load Control Valve and Surge Control Valve),

- A/C demands: Main Engine Start (MES) and Environmental Control

System (ECS).

MONITORING

To help maintenance and troubleshooting, the load control valve and the

surge control valve are equipped with visual position indicators.

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The ECB receives feed back signals about the position of the IGVs, the

load control valve and the surge control valve.

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GENERAL ... MONITORING

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APU SYSTEM MANAGEMENT D/O (3)

APU START SEQUENCE

Auxiliary Power Unit (APU) normal operation, starting and shutdown,

are initiated from the APU control panel but controlled and monitoredby the ECB.

Following conditions will be controlled and monitored:

- APU start,

- APU on-speed,

- APU normal shutdown,

- APU protective shutdown,

- APU emergency shutdown.

When the MASTER SWitch P/B is set to ON:

- the ON light comes on,

- the Electronic Control Box (ECB) is energized,

- the ECB starts the power-up test,

- the ECB exchanges data with the Data Memory Module,

- the APU LP valve opens,

- the APU fuel pump is energized if fuel system pressure is low,

- the APU air intake flap opens.

- the ECAM APU page comes into view.

When the START P/B is set to ON:

- the ON legend comes on,

- the ECB energizes the back-up start contactor and the start contactor

when these conditions are present: air intake flap open, power-up test

complete, data exchange between data memory module and ECBcomplete,

- the contactors energize the starter motor and causes the APU main shaft

to start to turn,

- the igniter is energized at 7%,

- the de-oil valve opens with the oil/fuel temperature and altitude.

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APU START SEQUENCE

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APU START SEQUENCE

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APU ACCELERATION SEQUENCE

APU AT 7% RPM

At 7% speed:- the ECB opens the fuel solenoid valve and combustion occurs,

- the Inlet Guide Vanes (IGVs) close,

- Ignition ON.

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APU ACCELERATION SEQUENCE - APU AT 7% RPM

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APU ACCELERATION SEQUENCE (continued)

APU AT 50% RPM

At 50% speed:- the ECB de-energizes the start contactor, above 20,000 ft at 58%,

and causes the starter motor to stop and continues to increase the speed

of the APU automatically,

- the ECB de-energizes the back-up start contactor.

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APU AT 60% RPM

At 60% speed:- the ECB de-energizes the ignition unit,

- the ECB de-energizes the de-oil solenoid, if it is open.

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APU AT 95% RPM

At 95% speed:- the IGVs move to 22 degrees' open position to prevent overheating,

- the ECB controls and monitors the APU automatically,

- the ON light in the START P/BSW goes off,

- the green AVAIL legend in the START P/BSW comes on.

- the APU generator can operate and APU bleed be switched to ON.

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APU AT 100% RPM

At steady state speed, an on-speed governor loop controls the fuelflow to the APU. With APU bleed selected to OFF or in ECS mode

the APU speed is 99%. When in Main Engine Start (MES) mode or

always when the aircraft is in flight, the APU speed is 100%.

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APU ON-SPEED

When the APU generator operates, the generator output parameters come

into view on the ECAM system page. When the APU bleed is switchedto ON, bleed parameters are displayed on the ECAM system page. The

ECB opens the Load Control Valve in accordance to the Bleed Monitoring

Computer (BMC) signal coming from the APU Bleed P/B.

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APU ON-SPEED

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APU NORMAL SHUTDOWN

When the MASTER SW is OFF, the ECB closes the IGVs to the minimum

position of 15°, the load control valve closes if it is open, the surge controlvalve opens and the cool-down cycle of the APU starts.

The cool-down cycle lets the APU operate for 60 seconds at a low

stabilized temperature. It starts when the ECB receives the closed signal

from the load control valve. If the load control valve was not in the open

position, the ECB supplies a signal to simulate an overspeed condition,

which causes the fuel solenoid to close and starts the APU shutdown

immediately.

Overspeed test occurs when the cool-down cycle is complete. The ECB

supplies a signal to simulate an overspeed condition, that causes the fuel

solenoid to close, and starts the APU shutdown.

It is possible to command an APU re-start during the shutdown sequence.APU speed must be below 7% before the starter motor is re-engaged.

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APU NORMAL SHUTDOWN

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APU NORMAL SHUTDOWN (continued)

APU AT 95% RPM

At 95% speed, APU "AVAIL" lights go off.

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APU NORMAL SHUTDOWN - APU AT 95% RPM

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APU AT 50% RPM

At 50% speed, the de-oil solenoid valve opens to decrease drag duringthe next start.

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APU NORMAL SHUTDOWN - APU AT 50% RPM

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APU BELOW 7% RPM

At and below 7% speed:- the de-oil solenoid closes,

- the APU fuel LP valve closes,

- the data memory module is updated,

- the air intake flap closes,

- the ECB de-energizes itself.

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APU NORMAL SHUTDOWN - APU BELOW 7% RPM

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APU PROTECTIVE SHUTDOWN

When the ECB is energized, it controls the APU starting and operating

phases. If an abnormal parameter is found, it starts an immediate shutdownwithout time delay, even if the APU bleed air is in use.

The ECB protective shutdown parameters are:

- overspeed,

- ECB failure,

- underspeed,

- overtemperature,

- loss of speed,

- sensor failure: thermocouples, low oil level and Low Oil Pressure (LOP)

switch failure,

- no flame,

- flap not open,- High Oil Temperature (HOT),

- LOP

- no speed,

- inlet overheat,

- no acceleration,

- clogged oil filter,

- main power stop.

APU EMERGENCY SHUTDOWN

The ECB starts an emergency shutdown when the APU FIRE P/B, in thecockpit, is released out or when the APU SHUT OFF P/B, on the external

power receptacle panel, is pushed. The ECB starts an automatic

emergency shutdown when an APU fire is found on ground. The APU

stops immediately without time delay, even if the APU bleed air system

is in use.

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APU PROTECTIVE SHUTDOWN & APU EMERGENCY SHUTDOWN

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APU WARNINGS (3)

EMERGENCY SHUT DOWN

If an EMERgency SHUT DOWN occurs, the single chime sounds, the

MASTER CAUTion and the MASTER SWitch FAULT lights come on.

The failure is shown amber on the EWD associated to indications on the

Auxiliary Power Unit (APU) ECAM page. An EMER SHUT DOWN

occurs when:

- the APU shut-off P/B is pressed on the external power control panel,

- the APU FIRE P/B is released out on the overhead panel,

- the automatic fire extinguishing logic is triggered on ground.

AUTOMATIC SHUT DOWN

If an AUTOmatic SHUT DOWN occurs, the single chime sounds, the

MASTER CAUTion and the MASTER Switch FAULT lights come on.

The failure is shown amber on the EWD associated to indications on the

APU ECAM page. An AUTO SHUT DOWN occurs in case of:

- overspeed,

- overtemperature,

- Low Oil Pressure (LOP),

- High Oil Temperature (HOT),

- no flame,

- no acceleration,

- low acceleration rate,

- deceleration during start sequence,

- surge/reverse flow,- generator high oil temperature,

- loss of DC power,

- underspeed,

- loss off speed,

- sensor failure,

- air intake not open,

- ECB failure.

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EMERGENCY SHUT DOWN & AUTOMATIC SHUT DOWN

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ECB INTERFACES (3)

POWER SUPPLY

One of the A/C batteries at the minimum and the A/C DC network,

electrically supply the Electronic Control Box (ECB), through the MAIN

control relay of the Auxiliary Power Unit (APU).

MASTER SWITCH P/B

The APU MASTER SWITCH sends a discrete supply or stop signal to

the ECB. The ECB sends a discrete signal to the FAULT light, when an

automatic shutdown occurs or if there is an emergency shutdown.

AIR INTAKE FLAP

The ECB receives an air intake flap open or closed position signal and

sends a power output to open or close the air intake flap.

START P/B

A discrete input signal from the START P/B starts the starting sequences.

The ECB sends a discrete signal to the ON light during the APU start

sequence. A discrete output signal to the A/C energizes the AVAIL light

in the START P/B when the APU speed is above 95%.

BACK-UP AND MAIN START CONTACTORS

The ECB receives a discrete input from the main start contactor and sends

discrete outputs to the back-up and main start contactors.

EMERGENCY STOP

A discrete input signal from the A/C starts the APU emergency shutdown

logic after the ECB receives this signal.

LGCIU 1

The ECB receives the aircraft on ground discrete input signal from

Landing Gear Control and Interface Unit (LGCIU) 1.

APU FUEL FEED SYSTEM

The ECB receives a discrete signal from the APU low fuel pressure

switch. It sends a discrete signal to the APU fuel LP shut-off valve.

EIU

During engine starts, the ECB receives a Main Engine Start (MES) signal

from Engine Interface Unit (EIU) 1 or 2. This signal causes the ECB to

set the Inlet Guide Vanes (IGVs) to the fully open position if APU bleed

has been selected to ON.

BMC

When the APU BLEED P/B is set to ON, Bleed Monitoring Computer

(BMC) 1 or 2 sends a discrete input to the ECB. This controls the APU

load control valve to open. The BMCs receive a closed-position signal

from the APU load control valve to monitor the pneumatic system and

to show ECAM indications.

TSO/JAR

The ECB receives a discrete input from the TSO/JARconfiguration-programming pin. This open or ground signal finds if the

ECB obeys the Technical Standard Order (TSO) or the Joint Aviation

Requirements (JAR). Concerning the JAR, all System Display (S/D)

circuits are available in flight. This configuration is the standard

configuration. For TSO, only emergency, overspeed and loss of speed

shutdowns, are available in flight.

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ENVIRONMENTAL CONTROL SYSTEM (ECS)

The ECB receives, via an ARINC 429 bus, an input from the Air

Conditioning System Controller 1 and 2 (ACSC) to control the IGVs

position according to the demand. The ECB sends a discrete output to

the ACSC 1 and 2 to signal that the APU bleed valve is en deliveryposition.

A320/A321 IDENTIFICATION

The ECB receives a discrete input from the A/C signature PIN

PROGramming. This identification pin lets the ECB identify A321

applications for functional differences from those of an A320.

SDAC

The ECB sends to System Data Acquisition Concentrators (SDACs) 1

and 2, through ARINC 429 Data buses, the indications to show on theECAM APU page and shutdown information to start the related warnings.

CFDS

The ECB is a BITE system type-1 computer and connects to the

Centralized Fault Display System (CFDS) through ARINC 429 data

buses.

DMU PART

The Data Management Unit (DMU) part of the Flight Data Interface and

Management Unit (FDIMU) partially keeps APU lifetime data. This

information lets you monitor the engine conditions.

DATA MEMORY MODULE

A data memory module installed on the APU inlet plenum keeps and

interchanges many parameters with the ECB:

- APU serial number,

- APU operating hours and starts,

- APU accumulated hot time,

- APU accumulated shutdowns, etc.

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POWER SUPPLY ... DATA MEMORY MODULE

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APU DRAIN SYSTEM PRESENTATION (2)

FUEL/OIL PUMP DRAIN

The fuel and oil pump seal drain line is routed via a collector line to the

drain tank. This line drains fuel or oil leaks.

DRAIN PORT AIR CHECK VALVE

An air check valve, mounted on the Fuel Control Unit (FCU) drain line,

prevents air ingestion in the FCU.

GEARBOX VENT

The accessory gearbox is vented to the Auxiliary Power Unit (APU)

exhaust through a vent line. This line vents gearbox air to the APU

exhaust.

IGV ACTUATOR DRAIN

The Inlet Guide Vane (IGV) actuator drain line is routed via a collector

line to the drain tank. This line drains only fuel leaks.

FLOW DIVIDER DRAIN

The fuel flow divider and drain valve drain line is routed via a collector

line to the drain tank. This drain line collects fuel purged from the nozzles

and the manifolds at APU shutdown.

TURBINE PLENUM DRAIN

The turbine plenum drain line is routed alone to the drain mast. This drain

line collects unburned fuel after a failed start attempt.

HEAT SHIELD DRAIN

The heat shield drain line is routed to the drain mast. This drain line

collects fuel, water or air leaks.

EXHAUST COUPLING DRAIN

The exhaust coupling drain line is routed to the drain mast. This drain

line collects fuel, water or air leaks.

DRAIN TANK

For venting and evacuation, the drain tank is connected to the drain mast.

Airflow across the drain mast creates a vacuum in the drain line. The

suction effect produced at 200 kt, is sufficient to remove the contents of

the drain tank. A vent line ventilates the drain tank and drain lines. The

APU drain lines are connected to the right access door drain lines through

spring adapter kiss seals. The drain mast drains any fluid leakage from

the APU through four holes.

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FUEL/OIL PUMP DRAIN ... DRAIN TANK

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APU BASIC DESCRIPTION (3)

GENERAL

The Auxiliary Power Unit (APU) is of a modular design. The three APU

modules are:

- the power section,

- the load compressor,

- the Accessory Gearbox (AGB).

POWER SECTION

The compressor is of a single stage centrifugal compressor design. The

main components of the compressor are:

- the inlet plenum,

- the impeller and the diffuser,

- the Inlet Guide Vane (IGV) assembly,

- the compressor hub containment.

COMBUSTION CHAMBER

The combustion chamber is of a reverse flow annular design and is

installed inside the turbine plenum. The main parts of the combustion

chamber are:

- the inner combustion chamber shell,

- the outer combustion chamber shell.

The following components are installed on the combustion chamber:

- the igniter plug,

- the six fuel nozzles.

TURBINE

The turbine assembly drives the compressor, the load compressor and

the gear train of the AGB. The single stage radial inflow turbine includes:

- a cooled nozzle guide vane,

- a rotor,

- a diffuser exhaust pipe including a diffuser nozzle and seven radial

vanes.

LOAD COMPRESSOR

The load compressor is of a single stage centrifugal design. The main

components of the load compressor are:

- the inlet guide vane assembly,

- the load compressor impeller,

- the load compressor diffuser,

- the load compressor scroll.

INLET GUIDE VANES

The IGV assembly controls the amount of air flowing through the APU

load compressor. The 14 IGV' are moved simultaneously by a gear train

operated by a fuel driven actuator actuator.

ACCESSORY GEARBOX

The gearbox transmits the shaft power to the APU accessories and to the

APU generator, which are installed on the gearbox pads. The gearbox is

also the oil reservoir for the APU lubrication system. The components

mounted on the accessory gearbox are:

- the starter motor assembly,

- the cooling air fan assembly,

- the lubrication unit,

- the Fuel Control Unit (FCU),

- the AC generator.

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APU IGNITION & STARTING D/O (3)

STARTER CONTROL

The starting system rotates and accelerates the Auxiliary Power Unit

(APU) rotor through a clutch and gearbox. When the APU speed is about

50%, the start logic of the Electronic Control Box (ECB) cuts off the

supply to the start contactor, which switches off the starter motor. The

timed acceleration loop of the ECB causes the APU to accelerate to

governed speed.

APU START CONDITIONS

An electric DC motor starts the APU. On ground operation conditions,

the APU is started by the aircraft batteries or aircraft batteries in

combination with Transfomer Rectifier Units (TRUs). A start in flight

is possible up to an altitude of 11900 m (39000 ft.) with the use of

TRUs. A start in flight is possible up to an altitude of 7630 m (25000ft.) with the use of the aircraft batteries only.

For successful APU starting on ground or in flight, both batteries PB

must be switched to the AUTO position according to Airbus

procedures.

IGNITION CONTROL

The ignition system provides initial light-off of the fuel air mixture in

the combustion chamber. The ignition system includes:

- an ignition unit, which produces high voltage electrical energy,

- an ignition lead which delivers electrical energy to an igniter plugscrewed into the combustion chamber.

During starting, the ECB switches on the ignition between 7% and 95%.

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STARTER CONTROL & IGNITION CONTROL

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APU FUEL SYSTEM D/O (3)

GENERAL

The Auxiliary Power Unit (APU) fuel system operates fully automatically.

The APU fuel system includes:

- a Fuel Control Unit (FCU) which schedules the fuel flow,

- a flow divider and drain valve assembly which directs the fuel to the

nozzles.

FUEL CONTROL UNIT

The fuel flow into the fuel control unit passes through the inlet fuel filter

to the High-Pressure (HP) fuel pump, and then it goes through the HP

filter to:

- the Inlet Guide Vane (IGV) actuator to position the IGVs,

- the Torque Motor (TM) metering valve for flow control,

- the differential pressure regulator.

The metered fuel goes through the pressurizing valve to the fuel shut-off

solenoid valve. The fuel solenoid valve is normally closed. It is electrically

controlled to be opened by the Electronic Control Box (ECB) when the

speed is above 7% rpm. When the fuel solenoid valve is open, the

pressurizing valve ensures that the appropriate working fuel pressures

are available to the system. The HP fuel pump will produce more fuel

flow than required to support combustion under any given rpm. A

differential pressure-regulating valve bypasses the excess fuel back to

the filter inlet.

FLOW DIVIDER AND DRAIN VALVE ASSEMBLY

The purpose of the flow divider is to direct fuel to the primary and

secondary manifolds. Both manifolds supply duplex fuel nozzles. From

7% rpm, the primary nozzles are supplied with fuel above 7.5 psi.

Secondary nozzles are supplied above 150 psi during acceleration and

running phases.

TIME ACCELERATION RATE SCHEDULE

The time acceleration rate schedule controls the fuel in order to cause

the APU speed to increase at a constant rate without overtemperature. It

controls the fuel TM of the FCU. The ECB protective circuits are set to

shut down the APU if a start is initiated and:

- speed is less than 7% for more than 30 seconds,



- acceleration rate is below 0.2% per second with Exhaust Gas

Temperature (EGT) above 204°C,

- EGT is below 204°C with speed more than 7% for 15 seconds.

SPEED CONTROL

The ECB controls the speed by means of the fuel TM according to the

bleed air demand from the air conditioning system or for Main Engine

Start (MES). On ground, the ECB maintains the speed at 99% rpm if

APU bleed is switched off, or with bleed air demand from the air

conditioning system and ambient temperature below 25°C, 101% rpm

with bleed air demand from the air conditioning system and ambient

temperature above 30°C, or for MES. In flight, the ECB maintains speed

at 101% rpm.

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APU OIL SYSTEM D/O (3)

GENERAL

This system is made up of:

- oil reservoir,

- oil level switch,

- gearbox pressure regulator valve

- lubrication unit (including pressure pump, scavenge pumps, Pressure

Regulating Valve (PRV))

- oil cooler,

- one lubrication filter (mounted on lubrication unit) and one scavenge

filter,

- oil temperature sensor,

- de-oil solenoid valve.

OIL RESERVOIRThe sump of the Auxiliary Power Unit (APU) accessory gearbox is the

oil reservoir. Oil is serviced through either a pressure fill port or a gravity

fill port. The accessory gearbox sump contains 5.7 l (1.5 US gal) of oil.

An APU oil heater is installed on the APU gearbox. When the APU

MaSTeR SWitch is not on, the oil heater is supplied with 115V AC. The

heater is controlled on when the temperature

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SCAVENGE PUMPS

Two scavenge pumps return the oil to the accessory gearbox. One

scavenge returns the power section rear bearing oil. The other scavenge

pump returns the generator oil through a separate filter. Both pumps form

part of the lubrication module and are driven by the same shaft as the

pressure pump. Oil from the power section forward bearing, gearbox

bearings, gears and starter clutch returns by gravity.

OIL MONITORING

The ECB monitors the oil pressure and oil temperature.

The ECB will shut down the APU if:

- the Low Oil Pressure switch (LOP) senses pressure below 35 psi (2.38

bar),

- the High Oil Temperature switch (HOT) senses temperature above

152°C (305.6°F),

- the generator oil temperature is above 185°C(365°F).

DE-OIL SYSTEM

The de-oiling solenoid valve reduces the oil pressure pump load during

the APU start, especially during the cold start condition when oil has a

high viscosity. The valve is located on the upper right hand side of the

gearbox. A solenoid operates the valve position. The ECB controls the

solenoid in relation to the de-oiling solenoid logic.

The solenoid valve is open when:

- the APU speed is between 0% and 60% and the oil sump temperature

is below -6.7 C (20 F),

- the APU speed is between 95% and 7% during the APU shutdown

sequence,

- the aircraft altitude is more than 30.000 ft.

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GENERAL

The Auxiliary Power Unit (APU) load compressor supplies the APU

bleed air. The quantity of the supplied bleed air changes with the different

bleed air demand from the Environmental Control System (ECS) or if

the main engines are started. This system is made up of:

- Inlet Guide Vanes (IGVs),

- the Electronic Control Box (ECB) which provides information of ECS

load, Main Engine Start (MES) load, Exhaust Gas Temperature (EGT),

generator load,

- bleed (load) valve,

- surge control valve,

- cooling.

INLET GUIDE VANES

Depending on the load demand, the ECB adjusts the speed of the APU

and positions the IGVs to modulate the airflow available from the load

compressor. The IGVs are driven by an actuator operated by fuel pressure,

and controlled by a Torque Motor (TM) signaled from the ECB. During

the start sequence, the IGVs are fully closed below 50% rpm, 10° open

between 50% and 75% rpm and 22° open above 75% rpm. The minimum

open or idle position of the IGVs, when the APU is running, is 22°. The

maximum open position of the IGVs is 88°. Above 23000 ft, the IGVs

assume the idle position and below 21000 ft they will open on demand.

ECS LOAD

In response to the ECS signal coming from the zone controller, the IGV

position may not exceed limits set in the ECB. APU speed is 99% rpm

if ambient temperature is or falls below 25°C (+77°F) or 101% rpm if

temperature is or rises above 30°C (86°F). The IGVs modulate within

limits. The ECS limits are: ECS MIN, ECS COLD, ECS NORMAL, ECS

HOT, memorized by the Erasable Programmable Read Only Memory

(EPROM) which is part of the ECB.

MES LOAD

In response to the MES signal coming from the Engine Interface Units

(EIUs), the ECB sets the IGVs to the fully open position. The IGVs are

fully opened. The APU speed is controlled to 101%. The MES load is

limited by an MES limit set in the ECB and memorized by the EPROM.

EGT

The bleed airflow is reduced as a function of the compressor inlet

temperature and the EGT. The EGT cannot exceed a limit set in the ECB.

T2 is the Load Compressor Inlet Temperature (LCIT). T5 is the EGT.

The EGT limit is set in the ECB and memorized by the EPROM.

NOTE: The APU bleed air system is used for MES and ECS.

GENERATOR LOAD

If the APU load is high and EGT increases to its limit, the ECB reduces

the bleed air load by controlling the IGVs to close. If a generator shock

load occurs, speed decreasing by more than 10% rpm per second, the

IGVs are closed for 3 seconds.

BLEED VALVE

The bleed air delivered by the load compressor is ducted to the aircraft

pneumatic system via the bleed (load) valve. The bleed valve is

electrically controlled and pneumatically operated. Each Bleed Monitoring

Computer (BMC) sends an opening signal to the ECB, which energizes

the bleed load valve solenoid only if the APU speed is greater than 95%

and no shutdown is initiated.

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SURGE CONTROL VALVE

The air delivered by the load compressor may be much more than the air

needed by the pneumatic system. The surge control valve discharges the

excess air into the APU exhaust. The ECB controls the surge valve via

a torque motor. To avoid compressor surge, a calculated airflow is

determined according to the IGV positions. The ECB compares the

compressor airflow rate, measured by using a total pressure transducer

at the load compressor outlet and a Differential Pressure (DELTA P)

transducer, with the calculated airflow. The airflow difference repositions

the surge valve. When the bleed load valve is open, the surge control

valve tends to close. During MES, the surge valve modulates to give a

constant bleed air pressure.

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GENERAL ... SURGE CONTROL VALVE

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COOLING

A gearbox driven cooling fan draws the air from the inlet plenum and

forces most of it through the oil cooler. The remaining air is used for

APU compartment ventilation.

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COOLING

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RUNNING SEQUENCE - AIR INTAKE FLAP SEQUENCE

When the APU MASTER SWITCH is set to ON, the Electronic Control

Box (ECB) is electrically supplied and initiates a power-up test. The

Auxiliary Power Unit (APU) fuel system is energized and the air intakeflap is controlled to open. The APU fuel LP valve opens and the APU

fuel pump logic is energized. The APU fuel pump will run as long as the

main engine fuel feed line pressure is lower than 23 psi (1.56 bar). The

ECB controls the opening of the air intake flap. When it is fully open, in

20 seconds, the ECB receives a flap open signal.

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RUNNING SEQUENCE - START SEQUENCE

Then, when the START P/B has been pressed, the ECB initiates the start

sequence by closing the start contactors only if the listed conditions are

met. The start contactors are closed if:- the power-up test is completed,

- the APU speed is less than 7 % rpm,

- no shutdown is initiated.

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RUNNING SEQUENCE - ACCELERATION SEQUENCE

The APU spool speed is monitored by two identical speed sensors

installed on the gearbox casing. The ECB takes into account the highest

speed signal for APU control and ECAM display. N represents thepercentage of APU rpm.

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(continued)

APU AT 7% RPM

At 7%, the ECB energizes the igniter and opens the fuel solenoid

valve on the Fuel Control Unit (FCU). The ECB also sets the correct

metered quantity of fuel for engine light-up. The metered quantity of

fuel is adjusted by the fuel Torque Motor (TM).

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(continued)

APU AT 50% RPM

The light-up phase is confirmed by the increase in Exhaust Gas

Temperature (EGT). This temperature is monitored by two sensors,

which send a signal to the ECB. The ECB takes into account the

highest temperature value for APU control and EGT ECAM display.

The EGT increases as the APU accelerates, with starter motor

assistance to 50% rpm where the ECB cuts off the electrical supply

to the start contactors. At 50% rpm, the Inlet Guide Vanes (IGVs)

move to 10° open to avoid compressor surge. Above 50% rpm, the

APU continues to accelerate under its own power to governed speed.

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