Chapter 6.70 - APU

Question 1

How many packs can the APU operate on the ground?

In the air?

How many AC transfer busses can the APU power on the ground?

In the air?

Answer 1

Both packs

One pack

Both AC transfer busses

Both AC transfer busses

Question 2

What fuel tank supplies the APU?

How is the fuel fed to the APU?

Answer 2

From the number 1 tank

• Fed by AC pumps, or
• Suction fed if they are not operating

Question 3

How long should you let the APU stabilize before using it as a bleed air source?

Answer 3

One minute

Question 4

What causes an auto APU shutdown?

Answer 4

• Battery switch off
• Overspeed
• Low oil pressure
• High oil temperature
• APU fire
• Fuel control unit failure
• High EGT
• Other system faults

Question 5

Can the APU be operated with the blue MAINT light illuminated?

Answer 5

Yes

Question 6

What is indicated by the amber APU LOW OIL PRESSURE light?

Answer 6

Oil pressure is low (always displayed unit APU start cycle is complete)

Question 7

What is indicated by the amber APU OVERSPEED light?

Answer 7

• APU RPM limit has been exceeded, or

- The overspeed self-test failed during a normal APU shutdown

Question 8

What are the APU altitude limits?

Answer 8

• APU bleed and electrical - 10,000 feet
• APU bleed - 17,000 feet
• APU electrical load - 41,000 feet

Question 9

What is the APU starter duty cycle limit?

Answer 9

15 minute cooling is required after third start attempt