APU

Question 1

List the limitations for bleed air usage and electrical Power usage?

Answer 1

Bleed air: 22’000ft

Electrical Power: 43’100 ft max certified alt

Question 2

Which starter has priority?

Answer 2

The ATS (Air Turbine Starter)

Question 3

What supplies Power for the APU electrical starter?

Answer 3

A dedicated APU battery

Question 4

Can a ground cart be used to start the APU?

Answer 4

Yes

Question 5

Which AC fuel pump runs automatically for APU operation?

Answer 5

The one from left fuel manifold

Question 6

What fuel pump is activated if the AC is not working for APU start?

Answer 6

Left DC fuel pump

Question 7

When does the starter engage and disengage?

Answer 7

Engage: When inlet door reaches full open position
Disengage: APU reaches 50%

Question 8

What are the conditions for an APU autostart?

Answer 8

If both AC transfer busses loses power

Question 9

What are the APU:s operating modes?

Answer 9

Attendend and Unattended

Question 10

What will cause an APU automatic shutdown in the Attended mode?

Answer 10

1. APU fire/inlet over temp
2. Overspeed
3. APU controller failiure
4. Speed droop

Question 11

Does the APU perform a cooldown during an automatic cooldown?

Answer 11

No

Question 12

What does the APU message APU LIMIT indicate during attended mode operation?

Answer 12

1. High EGT
2. High oil temp
3. Low oil pressure

Question 13

When is the APU operating in Unattended mode?

Answer 13

Basically on the ground when engines are not operating

Question 14

How is the APU shut down after an Auto start?

Answer 14

Position the APU selector to ON and then to OFF

Question 15

Describe the starting sequence for the APU?

Answer 15

BAT ON
Select start on APU selector, springloaded back to ON
APU inlet door opens
L FWD AC fuel pump or DC pump is energised
Fuel valve opens
If sufficient bleed air in the duct the APU bleed valve opens which allows operation of the ATS

Question 16

Why is Power from the main battery needed for APU start?

Answer 16

Power is needed to operate

1. APU inlet door
2. Fuel valve
3. Fire detection

Question 17

What happens if there is not enough bleed air avialable for the ATS?

Answer 17

An electrical starter is used

Question 18

What happens in flight when main GEN and back-up GEN goes off-line?

Answer 18

The APU starts automatically even with the switch to OFF

Question 19

Describe shutdown procedure for the APU

Answer 19

Select switch to OFF
APU bleed load is removed
APU COOLDOWN comes up on EICAS
APU is now in a 105 sec cooldown cycle. After 105 sec the fuel valve closes, the inlet door closes and the cooldown message is removed. Fault lights illuminates momentarily

Question 20

What does “Attended Mode” mean?

Answer 20

Means that there less faults that will cause automatic shutdown since engines are running a someone probably is looking after the status of the aircraft