APU

Question 1

What is provided by the APU?

Answer 1

• Provide bleed for engine start
• Provide AC electrical source
• Air for air conditioning Packs

Question 2

What are main components of the APU?

Answer 2

• Engine
• ECU
• Inlet Door
• Assembly gear box
• Lubrication system

Question 3

Which part of the APU provides bleed air?

Answer 3

APU engine compressor. The vanes are used to regulate airflow depending on the demand

Question 4

Where is APU ECU located?

Answer 4

In mid equipment bay

Question 5

How is APU start supplied

Answer 5

Primarily by DC ESS BUS 2 (from battery)
Secondarily DC EMER BUS

APU needs DC Power to start

Question 6

What is APU BITE test?

Answer 6

The ECU is continuously self-monitoring. It initiates an internal power-up
BITE test when either BATT 1 or BATT 2 switch on the ELECTRICAL
panel is set to AUTO. If it fails the BITE test, the FAIL light on the APU
panel comes on and the APU FAULT advisory message is displayed on
the EICAS page

Question 7

Where are APU OFF switches located

Answer 7

Question 8

What are possible positions of APU door?

Answer 8

The
position of the inlet door is either fully open, intermediate, or fully closed.

Question 9

What is the function of APU door?

Answer 9

The inlet door directs air into the APU and splits the air into two sections.
Some air is directed to the APU compressor and the rest cools the APU
compartment.

Question 10

What are paremeters of APU generator?

Answer 10

3-phase, 115V, 400 HC AC generator

Question 11

How is fuel provided to APU with engines off?

Answer 11

By suction feed, controlled by the ECU and fuel control unit

Question 12

How is fuel provided to APU with engines ON?

Answer 12

Left engine fuel ejector pump, and if AC boost pumps are operating

Question 13

What is needed to start the APU?

Answer 13

The APU requires either the Transformer Rectifier Unit 3 (TRU 3) when
external AC power is available, or both batteries for starting.

Question 14

How is energy split when only batteries are used for Engine start with APU?

Answer 14

When the batteries are used to start the APU, battery 1 powers the ECU while battery 2 turns the APU starter.

Question 15

Describe APU start sequence with ground power available

Answer 15

• Commands an APU BITE test,
• Opens the APU inlet door,
• Opens the APU fuel shutoff valve,
• Turns on the left AC fuel boost pump (on the ground with left engine
  off and AC power available), and
• Begins the APU start sequence begins and APU IN START shows in EICAS

Question 16

APU star limitations?

Answer 16

Max 3 times per hour, with 2 minuted between each start. ECU will prevent APU start if APU RMP is above 7%.

Question 17

How long is the APU colldown before APU dorr closes?

Answer 17

60 seconds

Question 18

What causes ECU to shutdown APU in air and on ground?

Answer 18

Question 19

Where is APU bleed shutoff switch located?

Answer 19

Air Panel on Overhead panel

Question 20

Can APU generator be disconnected to the Electrical system?

Answer 20

Yes, witht he APU GEN switch on the ELECTRICAL overhead panel

Question 21

When is APU FAIL displayed?

Answer 21

IF APU Fails to start
IF BITE test fails
IF APU fire is detected on ground (in this case EICAS SHUTDOWN)
IF AOU fire detection fails ground

Question 22

Does APU FAIL light extinguish if APU is shut down?

Answer 22

Yes

Question 23

What is APU GCU?

Answer 23

APU generator control unit

Question 24

What does the APU Fire switch do?

Answer 24

• closes APU shutoff valve
• closes APU bleed air valve
• deactivates APU generator
• commands APU shutdown
• arms APU extinguisher bottle

Question 25

When the aircraft is on the ground or in flight, and a critical ECU fault occurs, the APU will

Answer 25

Shut down immediately

Question 26

if no AC power available or the left engine is not operating, fuel is supplied to the APU by

Answer 26

Suction feed

Question 27

when the left engine is operating, Fuel is supplied to the APU by

Answer 27

The left engine main fuel ejector pump

Question 28

The main purpose of the APU is to provide an alternate source of

Answer 28

Bleed air during ground and flight operations and AC electrical power

Question 29

The APU can be started with which of the following power sources?

Answer 29

External power Both aircraft batteries AC power through transformer rectifier unit 3 (TRU 3)

Question 30

Which of the following conditions will cause the APU to shutdown automatically on the ground or in flight?

Answer 30

Failed/slow/hot/hung start

Question 31

Select the three conditions that illuminate the APU FAIL light.

Answer 31

Failed start Failure of built-in-test APU fire detection fails on the ground

Question 32

When the APU rotary switch is placed to the START position for three seconds:

Answer 32

The APU fuel shutoff valve opens

Question 33

What controls the APU inlet door position?

Answer 33

Electronic control unit (ECU)

Question 34

The main purpose of the APU is to provide an alternate source of ____. (Select two responses.)

Answer 34

bleed air during ground and flight operations. AC electrical power.

Question 35

When does the electronic control unit (ECU) initiate an automatic shutdown in flight?

Answer 35

When a critical ECU fault occurs (i.e. loss of DC power)

Question 36

How is APU oil cooled?

Answer 36

By an air/oil heat exchanger

Question 37

Does APU FAIL light stay on when APU is swithced off?

Answer 37

No

Question 38

What type of power APU can generate?

Answer 38

APU can generate 75 kVA AC

Question 39

Important note for LAND 2 operations and NAV sources?

Answer 39

NOTE: Manual tuning all of the navigation sources and setting the inbound courses is required for LAND 2 operations.

Question 40

How is fuel provided to the APU? 1) if engines are running? 2) if AC Power not available?

Answer 40