APU

Question 1

What is an APU?

Answer 1

A single-stage gas turbine engine that provides pneumatic air and AC power.

Controlled by its own FADEC.

Question 2

How is the APU fuel supply normally fed?

Answer 2

Normally fed from the right wing tank.

Can also be fed from the left tank via the crossfeed valve (XFEED LOW 2).

Question 3

What supplies fuel pressure if AC power is available and the engine is not running?

Answer 3

The AC fuel pump provides fuel pressure.

Question 4

What does the APU bleed provide air for?

Answer 4

Air conditioning, pressurization, and water pressurization.

Question 5

What does the FADEC monitor for APU operation?

Answer 5

Critical/major faults and will command shutdown based on specific conditions.

Question 6

What are the automatic shutdown conditions in flight?

Answer 6

Overspeed, underspeed, and FADEC critical fault.

Question 7

What are the automatic shutdown conditions on the ground?

Answer 7

Overspeed
underspeed,
FADEC critical fault,
fire,
overheat,
high oil temperature,
low oil pressure,
sensor failure.

Question 8

How is normal start/shutdown controlled for the APU?

Answer 8

By the APU selector knob.

Question 9

What happens when the APU selector knob is set to ‘OFF’?

Answer 9

Removes pneumatics only, placing the APU into a 1-minute cool down period before shutting it down.

Question 10

How can you cancel the shutdown during the cool down period?

Answer 10

Reselect the selector knob to the ‘ON’ position within 1 minute.

Question 11

What is the purpose of the EMER STOP button?

Answer 11

Used for an abnormal shutdown without a 1-minute cool down period.

Question 12

When will electrics and pneumatics be available after starting the APU?

Answer 12

Usually around 95% plus 3 seconds after the APU is started.

Question 13

What kind of APU is on the aircraft?

Answer 13

Sundstrand APS 2300

Question 14

Describe the APU.

Answer 14

Constant speed
Single-stage impeller with a 2-stage axial-flow turbine
Independent oil system

Question 15

Does a FADEC control the APU

Answer 15

YES

Question 16

What battery is used for the APU start?

Answer 16

BATT 2 powers the starter
BATT 1 powers the FADEC and EICAS for monitoring

Question 17

What is the fuel source for the APU?

Answer 17

Right fuel tank
Left fuel tank through the crossfeed valve

Question 18

What fuel pump is used for APU start?

Answer 18

Batteries ‘ON’ only DC fuel pump in right tank
AC powered airplane ACMP 2
Right engine running Ejector fuel pump

Question 19

Will the APU shutdown automatically if speed and acceleration rate isn’t reached in starting cycle time?

Answer 19

Yes

Question 20

What does moving the APU start switch to ‘OFF’ do?

Answer 20

Initiates normal APU shutdown
1-minute cool down
No pneumatics (electrics only for 1 minute)

Question 21

Can the APU shutdown be cancelled?

Answer 21

Yes, by moving the START switch back to ‘ON’ before the 1-minute cool down is over

Question 22

How is the APU shutdown immediately?

Answer 22

APU emergency stop button

No 1-minute cool down period

Question 23

What will happen if batteries are turned OFF during the 1-minute cool-down period?

Answer 23

APU will shut down immediately

Question 24

When will automatic shutdown of the APU occur on the ground?

Answer 24

Automatic shutdown of the APU on the ground will occur due to:
- Overspeed
- Underspeed
- FADEC critical fault
- Fire
- Overheat
- High oil temperature
- Low oil pressure
- Sensor failure

Question 25

When will automatic shutdown of the APU occur in flight?

Answer 25

Automatic shutdown of the APU in flight will occur due to:
- Overspeed
- Underspeed
- FADEC critical fault

Question 26

Can the APU be started after a critical fault?

Answer 26

No