Auxillary Power Unit System

Question 1

(B) What kind of APU is on the aircraft?

Answer 1

Hamilton Sundstrand APS 2300

Question 2

(B) Describe the APU?

Answer 2

• Constant Speed
• Single stage centrifugal compressor
• Reverse flow annular combustor
• 2-Stage axial-flow turbine mounted on a common rotor shaft

Question 3

(B) What controls the APU?

Answer 3

A dedicated FADEC

Question 4

(B) What battery is used for the APU start?

Answer 4

• BATT 2 powers the starter

- BATT 1 powers the FADEC and EICAS monitoring

Question 5

(B) What is the fuel source for the APU?

Answer 5

• Right fuel tank

- Left fuel tank through the crossfeed valve

Question 6

(B) What fuel pump is used for APU start?

Answer 6

• Batteries ON only DC fuel pump in right tank
• AC power from ACMP 2
• Right engine running ejector fuel pump

Question 7

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

Answer 7

Yes

Question 8

(B) What does moving the APU start switch to OFF do?

Answer 8

• Initiated normal APU shutdown
• 1-minute cool down
• Pneumatics CUT OFF and Electrics on for 1 minute

Question 9

(B) 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

(B) What will happen if batteries are turned off during the 1-minute cool-down period?

Answer 10

APU will shut down automatically

Question 11

(B) when will automatic shutdown of the APU occur?

Answer 11

Ground
- Overspeed
- Underspeed
- FADEC critical fault
- Fire
- Overheat
- Low oil pressure
Flight
- Overspeed 
- Underspeed 
- FADEC critical fault

Question 12

(B) Can the APU be started after a critical fault?

Answer 12

NO

Question 13

(T) What does the APU gearbox do?

Answer 13

• Reduces engine rotor speed to drive the Oil Cooled AC Generator
• Drives the oil pump assembly

Question 14

(T) Explain operation of the APU?

Answer 14

1. Switch to ON - Powers up the FADEC
2. Switch to start - FADEC energizes starter controller to start turning the turbines with the starter and opens the APU SOV
3. APU speed approx. 7%, the FADEC allows the FCM to open to introduce fuel and starts the igniters
4. At 50% APU speed, FADEC de-energizes the exciter and starter
5. 95% + 3 seconds, pneumatic and electrical power is available and displayed

Question 15

(I) What is the difference between emergency and normal shut down?

Answer 15

• Emergency shut down - APU shut-off valve closes which does not allow for normal 1-minute cool down

Question 16

(O) How much fuel does the APU burn on the ground?

Answer 16

Average of 300lbs./hour