Auxiliary Power Unit

Question 1

What does the APU provide?

Answer 1

28V DC electrical power and bleed air while on the ground.

Question 2

Describe the APU Electrical System.

Answer 2

-One air-cooled, 28v, 400amp DC starter/generator which provides DC power to the Right Main DC Bus.

Question 3

Where does the APU draw its fuel from?

Answer 3

The left wing collector bay via a gravity fed, APU-driven fuel pump.

Question 4

When will the APU fuel shutoff valve automatically close?

Answer 4

• The PWR switchlight is pushed off
• An APU fire is detected.
• The EXTG switchlight on the APU section of the FPP is pushed.
• The APU Fire Test button is pushed.
• The aircraft becomes airborne with the APU running.
• An APU fault is detected.
• The APU Starter-Generator overheats

Question 5

When will the WARN segment of the GEN switchlight illuminate?

Answer 5

• The generator has not been selected on with the APU running.
• The GEN is selected on but has not come online, such as External Power is still connected.
• The APU is taken off-line due to a generator malfunction.

Question 6

What are the indications of a APU GEN overheat?

Answer 6

• GEN OHT advisory light illuminates
• APU FAIL advisory light illuminates
• WARN advisory light illuminates
• APU light on the CWP illuminates
• MASTER CAUTION illuminates

Question 7

Describe the APU Fire Protection System

Answer 7

A dedicated fire loop with a fire extinguishing bottle.

Question 8

What are the indications when a fire is detected by the APU Fire Protection System?

Answer 8

• APU Fuel Valve Closed (FPP)
• BTL ARM (FPP)
• EXTG Switchlight (FPP)
• FIRE advisory light (FPP)
• FAIL (APU Panel)
• APU (CWP)
• CHECK FIRE DETECT (CWP)
• MASTER CAUTION
• MASTER WARNING

The APU will automatically shut down and after 7 seconds the APU fire bottle discharges.

Question 9

What lights illuminate on a APU Fire Detection Test?

Answer 9

• APU Fuel Valve Closed (FPP)
• BTL ARM (FPP)
• EXTG Switchlight (FPP)
• FIRE advisory light (FPP)
• FAULT light (FPP)
• FAIL (APU Panel)
• APU (CWP)
• CHECK FIRE DETECT (CWP)
• MASTER CAUTION
• MASTER WARNING

Question 10

What faults will cause an automatic APU shutdown?

Answer 10

• Overspeed
• Underspeed
• Start sequence failure
• Acceleration failure
• EGT overtemp
• Low oil pressure
• High oil temp
• Fail sensors, valves or relays
• Internal Failure

Question 11

What are the APU starter cranking limitations?

Answer 11

60 seconds on - 5 minutes off

60 seconds on - Call Maintanence

Question 12

What bus powers the APU fire protection system?

Answer 12

Right Essential