15.18

Question 1

What does the APU do?

Answer 1

Provide pneubleed air and electrical power for aircraft systems

Question 2

The APU can be split up into three main sections

Answer 2

Power
Bleed
Accessory gearbox

Question 3

What does the power section of the APU do?

Answer 3

Drive the compressor and the gearbox

Question 4

What is the compressor called that provides sufficient bleed air to the pneumatic system

Answer 4

Load compressor

Question 5

What type of compressor will you find on APU

Answer 5

Centrifugal flow compressor

Question 6

On modern APUs the combustion chamber is what type

Answer 6

Annular type

Question 7

What is the air pressure for the APU

Answer 7

30-45psi

Question 8

What are the two methods of APU bleed air supply

Answer 8

Compressor of the the power section

Individual load compressor

Question 9

The airflow into the load compressor can be controlled by what?

Answer 9

Variable inlet guide vanes

Question 10

Why does the APU generator not need a constant speed drive when running as a back up

Answer 10

Because the APU is always controlled to a constant speed by the APU fuel control unit

Question 11

Where is the APU compartment located

Answer 11

In aircraft tail sections

Question 12

What does the APU equipment compartment house hold

Answer 12

Air intake actuator
APU fire extinguisher bottle
Fuel supply line
Bleed air duct

Question 13

How many APU mounts are there to support the APU

Answer 13

3 one is fixed the other 2 are flexible

Question 14

How many mounts transmit vertical loads and forces from the APU

Answer 14

2

Question 15

How many mounts transmit lateral loads and forces from the APU

Answer 15

1

Question 16

How many mounts transmit vertical loads and forces from the APU

Answer 16

All 3

Question 17

What equipment is used to remove the APU

Answer 17

Hoist equipment

Question 18

What is another name for the air intake door

Answer 18

Air intake flap

Question 19

What voltage is need to drive the APU air intake door actuator

Answer 19

28V DC power

Question 20

What does the APU inlet (diffuser) do?

Answer 20

Guides the air to the APU

Question 21

What does the APU air intake elbow do?

Answer 21

Forms the air duct between the air inlet duct and the APU air inlet

Question 22

What are the two types of drains

Answer 22

Direct and indirect

Question 23

What does the APU drain mast do

Answer 23

Collects the leakage and drains the fluid overboard during flight

Question 24

What two actions are needed to start the APU

Answer 24

Start initiation

Start activation

Question 25

What are the two APU control signals for constant speed control

Answer 25

APU speed signals | Torque motor signals

Question 26

How many ways can you turn off the APU

Answer 26

3 ways

Question 27

What is the cool down period of an APU

Answer 27

Between 0 and 120s

Question 28

How is automatic stut down of an APU activated

Answer 28

By the APU control unit

Question 29

What is the name of the primary fuel system of the APU

Answer 29

Low pressure fuel systems

Question 30

Where does the primary fuel system start and end

Answer 30

Starts at the fuel tanks and ends at the FCU of the APU

Question 31

Where does the secondary fuel system of the APU start and end

Answer 31

Starts at the FCU and ends at the fuel nozzle of the combustion chamber

Question 32

What are the sub-systems for the APU air system

Answer 32

Cooling air system and bleed air system

Question 33

What are the three main tasks of a bleed air system

Answer 33

Bleed supply Surge procreation Load compressor control

Question 34

Can a load compressor be switch off

Answer 34

No because it is fixed to the rotor shaft

Question 35

How can compressor surging be prevented

Answer 35

Bleeding off the air that is blocking the compressor discharge

Question 36

When would the surge control valve open

Answer 36

If the airflow behind the load compressor decrease or stops

Question 37

What are the two pressure pick ups in the surge protection system

Answer 37

Total pressure and static press

Question 38

What are the three types of supply pumps which can be used in the APU oil system

Answer 38

Gerotor type Gear type Vane type

Question 39

What pressure is the gearbox in the APU oil vent system pressurised to

Answer 39

4-5psi

Question 40

What does the APU starter lead do

Answer 40

Transmit the battery power to APU starter motor

Question 41

What type of motor is the starter motor

Answer 41

Brush type DC motor

Question 42

What are the three starter limitations for a APU battery

Answer 42

Duty time Cool down time Duty cycle

Question 43

The APU ignition system is usually powered by what?

Answer 43

DC

Question 44

What are the most important indication you will see during APU start

Answer 44

Battery voltage Speed indication EGT indication