APU Questions

Question 1

What kind of APU is on the aircraft?

Answer 1

• Sundstrand APS 2300

Question 2

Describe the APU

Answer 2

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

Question 3

What controls the APU?

Answer 3

• A dedicated FADEC

Question 4

What battery is used for the APU start?

Answer 4

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

Question 5

What is the fuel source for the APU?

Answer 5

• Right fuel tank
• Left fuel tank through the crossfeed valve

Question 6

What fuel pump is used for APU start?

Answer 6

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

Question 7

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

Answer 7

• Yes

Question 8

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

Answer 8

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

Question 9

Can the APU shutdown be cancelled?

Answer 9

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

Question 10

How is the APU shutdown immediately?

Answer 10

• APU emergency stop button
• No 1-minute cool down period

Question 11

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

Answer 11

• APU will shut down immediately

Question 12

When will automatic shutdown of the APU occur?

Answer 12

• Ground:
   Overspeed
   Underspeed
   FADEC critical fault
   Fire
   Overheat
   High oil temperature
   Low oil pressure
   Sensor failure
• Flight:
   Overspeed
   Underspeed
   FADEC critical fault

Question 13

Can the APU be started after a critical fault?

Answer 13

• No