ENGINE - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General
The APU supplies:

pneumatic power for 'Main Engine Start (MES)',
pneumatic power for the Environmental Control System (ECS),
mechanical shaft power to drive an AC generator and a fan. The fan cools the lubrication system and supplies the cool air to cool the APU compartment.

The APU supplies:

pneumatic power for 'Main Engine Start (MES)',
pneumatic power for the Environmental Control System (ECS),
pneumatic power for the Integrated Controlled APU to Rotate Engine (iCARE).
mechanical shaft power to drive an AC generator and a fan. The fan cools the lubrication system and supplies the cool air to cool the APU compartment.

** ON A/C NOT FOR ALL

2. System Description

Auxiliary Power Unit ** ON A/C NOT FOR ALL

The APU consists of two basic units:

A. Power/Load Compressor Section (Ref. 49-21-00)
The power section is essentially a single-shaft assembly with the following major components:

single-stage centrifugal compressor with a 7,5 : 1 pressure ratio.
reverse-flow annular combustion-chamber,
two-stage axial-flow turbine.
The load compressor is a direct-drive modular assembly, installed between the power section and the accessory gearbox. It is a single-stage centrifugal compressor with a compressor ratio of 4:1. Inlet guide vanes (IGVs) are installed at the entrance of the compressor housing to control the compressor output to the aircraft pneumatic system.

B. Accessory Gearbox (Ref. 49-26-00)
The accessory gearbox is installed on the end face of the load compressor casing and is driven by the power section. It has drive pads for:

an AC generator,
a starter motor,
a fuel-control unit and lube module,
a cooling fan.

** ON A/C NOT FOR ALL

3. Operation/Control and Indicating
The following components control APU start:

master switch 14KD (MASTER SW) and
APU start switch 2KA (APU START)

A. APU Start

(1) When the MASTER SW 14KD is set to ON, the ECB is energized.

energize the APU fuel-feed pump 4QC.

(2) This causes the ECB to transmit the following commands:

open the APU air-intake flap;
open the FUEL LP VALVE 3QF;

(3) After setting the APU START pushbutton to the 'ON'-position:

a signal is transmitted to the ECB.
When the intake is open, this is indicated to the ECB via the open position switch of the air intake door-actuator. When intake is open, the backup and main start contactors are energized and power is supplied to the starter motor.
When the back-up start contactor is activated, the ECB energizes the igniter and opens at 7% rpm the fuel solenoid valve on the Fuel Control Unit (FCU) to supply fuel to the Fuel Flow Divider (FDD). The fuel flow rate from the FCU is controlled by torque motor current from the ECB.
The starter motor 8KA assists the APU to accelerate to 50% rpm. Above 20,000ft it accelerates the APU to 58% rpm. The Exhaust Gas Temperature (EGT) increases at a related constant temperature as the APU accelerates.
The ECB controls the Inlet Guide-Vane Actuator (IGVA). Below 95% APU speed, the ECB signals the IGVA to move the Inlet Guide Vanes (IGVs) to the fully closed (15 degrees) position. Above 95% speed the IGV actuator receives signals to move the IGVs to 22 degrees open position. This allows a minimum amount of air to flow through the load compressor to prevent overheating. A timed acceleration sequence program in the ECB gives a controlled, constant acceleration.
When the engine has governed rpm (95% rpm + 2s), the ECB sends an 'AVAILABLE' signal to the aircraft circuits. The AVAIL legend in the APU START pushbutton switch 2KA comes on. It indicates that the APU is ready to supply bleed air and electrical power to the aircraft systems.

(4) When the APU BLEED pushbutton switch 5HV is set to the ON position:

the load control valve will open.
The APU will then supply bleed air to the pneumatic system. The ECB controls the load control valve, which supplies the pneumatic system with bleed air. The EGT increases when a selection of pneumatic or electrical load, or both, is made. This is shown on the lower ECAM display unit of the Electronic Centralized Aircraft Monitoring (ECAM).
When the engine speed has passed 95% rpm + 2s, the ECB will accept pneumatic demand signals.
It computes the position of the IGVs and supplies the necessary pneumatic flow. The pneumatic and electrical loads together can cause the EGT to increase more than the set temperature limit. If this occurs, the ECB commands the IGVs to move nearer to the closed position. This reduces the pneumatic load and makes the electrical load the primary load.

(5) When the MASTER SW 14KD is set to the OFF position, a normal APU shutdown starts. The ECB closes the APU load control valve.
With the pneumatic loads removed and the bleed air supply no longer required, the APU goes into a cool-down cycle. The cool-down cycle can be break off by setting the MASTER SW bck to the ON position.

At the end of the cooldown cycle, the ECB exercises the overspeed protection circuit by feeding a frequency input to the overspeed shutdown circuitry. This simulates an overspeed condition. In response, the fuel solenoid closes and the APU shuts down as it would for an actual overspeed condition.

Then the ECB removes the 'AVAIL' signal to the aircraft circuits. The AVAIL legend in the APU START pushbutton switch 2KA and AVAIL indications on the lower ECAM displays are then turned off.
During the APU rolldown, the ECB continues to function and maintain signals to the A/C circuits. The IGVs are positioned closed at 15 degrees. An APU restart may be initiated at any time, however the ECB will not initiate the restart until APU speed drops below 7%.

A decrease in the EGT shows on the APU page of the ECAM.
During the run-down cycle, when the engine speed is below 7% rpm, the ECB closes the air intake flap and the fuel low-pressure valve 3QF. Before it de-energizes itself, the ECB signals the aircraft circuits to:
close the FUEL LP VALVE 3QF.

The ECB continually monitors the APU operation and protection functions. If necessary, it shuts down the APU or gives a visual indication to the operator. When a malfunction occurs that could cause damage to the engine, the ECB automatically unloads the engine and starts a shutdown. The FAULT legend in the MASTER SW 14KD comes on. It will stay on until the MASTER SW 14KD is released to OFF.

** ON A/C NOT FOR ALL

4. Operational Characteristics

A. Operating Limits

(1) Rated combination load at sea level 38 DEG.C (100.40 DEG.F) condition:

Bleed Load: Bleed flow = 1.17 Kg/s (156 lbs/min),

Bleed pressure = 3.60 bar (52 psi),

Shaft load: 83KW (111.3 shp).

(2) Turbine discharge temperature (at rated combination load) maximum 640 DEG.C (1184.00 DEG.F) approximately.

(3) Turbine discharge temperature (governed speed, absolute maximum) 675 DEG.C (1247.00 DEG.F) approximately.

(4) Engine shaft speed

IDLE/MES and ECS Engine Speed Schedule ** ON A/C NOT FOR ALL

B. Fuel and Fuel Control System

NOTE: This is for general reference only. All fuel types approved in your Flight Crew Operation Manual (FCOM) can be used in the APU.

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Fuel Specifications

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Jet A/Jet A1 ASTM D 1655

JP4 Mil-T-5624

Jet B ASTM D 1655

JP5 Mil-T-5624

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(1) Fuel inlet pressure from 0.34 bar (5 psi) (min) above true vapour pressure to 3.8 bar (55 psi) (max).

(2) Fuel inlet temperature from - 40 DEG.C (-40 DEG.F) to 57 DEG.C. (135 DEG.F).

(3) Oil and Fuel leakage limits

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Unit/Item Maximum Remarks

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Fuel/Lube Module 0.33 cc/hour At the FCU/Lube

Cavity Drain Module tell-tale

Witness drain

+ + + +

IGV Actuator 0.33 cc/hour At the IGVA tell-tale

Witness drain

+ + + +

Surge Control 0.33 cc/hour At the SCV tell-tale

Valve (SCV) Witness drain

+ + + +

Oil Consumption 6.5 cc/hour This oil consumption

is only applicable for a

new or freshly refurbished

engine. It refers to the

oil lost inherently during

engine operation.

+ + + +

(a) The leakage rates shown in the table are acceptable for normal engine operation. Leakage more than the limits or a sudden leakage increase, must be monitored frequently and/or necessary maintenance scheduled.

(b) Fuel leakage from the muffler/combustor case drain is permitted only after an incorrect start or blowout.

(d) In case there are more than 0.33 cc/hour at the drain mast, do the necessary trouble shooting to isolate the source of the leakage.

C. Engine Starter Motor-Duty Cycle
Three consecutive start attempts are permitted without cooldown. After the third start attempt the starter motor must cool down for at least 60 minutes.

D. Lubrication System

Guideline for the Oil Consumption of the APU 131-9(A) in Service ** ON A/C NOT FOR ALL

(1) Oil specification - approved lubricants of vendor.

(2) Oil reservoir capacity 6.26 l (1.6537 USgal) approx.

(3) Oil consumption - monitor in accordance with the guideline for the oil consumption in service.

E. Electrical System:

(1) The ECB (59KD) is supplied with 28VDC by the busbar 301PP.

(2) The Starter Motor is supplied with 28VDC by the busbar 3PP.

F. Bleed-Air Control System

(1) Inlet Guide-Vane Actuator - Nonoperating - Closed.

(2) Surge Control Valve - Nonoperating - Open.

(3) Bleed Load Valve - Normal position - Closed.

[Rev.10 from 2021] 2026.04.01 01:28:34 UTC