Chapter 2 - APU

Question 1

What does APU stand for?

Answer 1

Auxillary Power Unit

Question 2

What are the 4 functions of the APU?

Answer 2

2 x Pneumatic

  - Power plant start
  - Provide air for ECS and ISDS

2x Electrical

 - Provide electrical power in normal situation
 - Provide electrical power in emergency situations

Question 3

Where is the APU located?

Answer 3

Rear of the main gearbox, right of No.2 engine

Question 4

What are the 3 major APU Modules, and what do they do?

Answer 4

Gearbox Module - contains reduction gearbox and associated accessory drives

Turbine Module - houses the intake, compressor rotor and turbine rotor

Combustor Module - houses the reverse flow combustion chamber and exhaust

Question 5

List the 9 major components of the APU

Answer 5

Air Intake
Exhaust
Air Delivery Pipe
Air Bypass Valve
Starter Motor
Fuel Filter
HEIE
Ignitor Plug
Fuel Control Unit

Question 6

What is the Air intake?

Answer 6

Channels airflow to compressor and AC Generator

Question 7

What is the exhaust?

Answer 7

Channels gases from the turbine to atmosphere

Question 8

What is the air delivery pipe?

Answer 8

Channels pressurised air from the combustor module to the pneumatic gallery

Question 9

What is the Air Bypass valve?

Answer 9

Channels air from the compressor to the exhaust to prevent over pressurisation

Question 10

What is the starter motor, and what is it powered by?

Answer 10

Starts the APU

Powered by a 28V DC battery

Question 11

What is the fuel filter?

Answer 11

Filters fuel of any unwanted dirt and debris

Question 12

What is the HEIE & Ignitor plug?

Answer 12

HEIE - High Energy Ignition Exciter
Converts Low tension electricity to high tension electricity
Ignitor plug creates a spark, supplying ignition to the mixture of air and fuel

Question 13

What is the Fuel Control Unit?

Answer 13

Provides a metered amount of fuel into the combustor module during all conditions of operation

Question 14

What is the main fuel manifold?

Answer 14

Delivers fuel to the 6 main fuel nozzles in the combustor module

Question 15

Name the components of the APU Lubrication system (6)

Answer 15

External Pipe
Low Oil Pressure Switch
Sight Glass
Magnetic Plug
Filler Cap
Filter

Question 16

What does the filter contain?

Answer 16

Bypass mechanism in case of blockage

Question 17

What does the magnetic plug do?

Answer 17

Collects any ferrous debris in the oil

Question 18

Where is the APU AC generator located, and what does it supply to the aircraft systems?

Answer 18

Front face of the APU

25kVa

Question 19

What does ESU stand for?

Answer 19

Electronic Sequencing Unit

Question 20

What does the ESU do?

Answer 20

Automatically controls the APU start sequence and monitors critical engine parameters

Question 21

What is the pneumatic gallery?

Answer 21

Pipe that delivers air from the APU to other engines

Question 22

What does the APU master start switch do?

Answer 22

isolates power from the APU start circuits

Question 23

What does the bleed switch do?

Answer 23

Selects the source of bleed air between ground use (OFF) engines or APU

Question 24

What does the APU Fuel/Fail indicator indicate?

Answer 24

Confirms a failure in either the booster pump supply or the APU system

Question 25

What does the Ready/Start indicator indicate?

Answer 25

APU mode of operation

Question 26

What does the Low Pressure fuel switch and indicator do?

Answer 26

Switch isolates APU from the fuel supply, energises the ESU and turns off APU Fuel pump

Indicator shows when the low pressure fuel is in the OFF position

Question 27

What does the APU Start/Stop button do?

Answer 27

provides an interface to start or stop the APU

Visually indicates fire warning

Question 28

Where are the APU Panel switches located?

Answer 28

Cabin, aft of the cargo door

Question 29

What does the APU cabin control panel consist of?

Answer 29

APU emergency stop switch
fire extinguisher switch
fire warning test switch