APU

Question 0

Where does the APU get its power for starting?

Answer 0

The Right Main 28vDC Bus

Question 1

Describe the APU on the Q400

Answer 1

Gas turbine engine drives an air cooled, 28vDC, 400 amp starter generator to provide DC power and air conditioning while on the ground. Has its own FADEC and Fire Protection.

Question 2

What does pushing the APU PWR switchlight do?

Answer 2

• Opens the APU Fuel Shutoff Valve (white light extinguishes, green light illuminates)
• Arms the APU Start Circuits
• APU performs a self test

Pressing the button again closes the APU Fuel Shutoff Valve

Question 3

What does pressing the START button on the APU panel do?

Answer 3

Once the PWR button is pressed and self test complete, pressing the START button begins the FADEC controlled start sequence. The STARTER light will extinguish and the green RUN light will illuminate on the PWR button approximately 20 seconds later. APU starter cutout occurs at approximately 50% operating speed.

Question 4

What happens if the APU is running, the GEN push button pressed in, the green RUN portion is illuminated and the DC External Power is switched to ON?

Answer 4

The APU DC Generator will be taken offline, the green RUN light will extinguish and the amber WARN light will illuminate.

Question 5

When will the APU provide bleed air to the ECS?

Answer 5

When the APU Bleed Switchlight is pressed in and both engine bleed selector switches are selected to the off position. Pressing the switch again closes the APU Bleed valve.

Question 6

If the APU Generator overheats the ________ light will be illuminated and _________.

Answer 6

GEN OHT light

The APU will automatically shut down

Question 7

What ensures that no engine bleed air enters the bleed air supply duct?

Answer 7

A check valve in the APU bleed duct and two check valves in the engine bleed ducts ensure neither bleed source can send air to the other (i.e. APU bleed air to the airframe deice system)

Question 8

In addition to providing bleed air to the ECS what else does the APU bleed air do?

Answer 8

Holds open the Aft Safety Outflow Valve

Question 9

Where does the APU get its fuel from?

Answer 9

The left collector bay

Question 10

When does the APU fuel shutoff valve automatically close?

Answer 10

• The APU PWR pushbutton is pushed off
• APU fire is detected
• GEN overheat
• The EXTG pushbutton on the APU Fire Protection Panel is pushed
• The APU Fire Test button is pushed
• The aircraft becomes airborne (WOW)
• APU fault is detected

Question 11

When will the APU FADEC command a shutdown?

Answer 11

Overspeed
Underspeed
High oil temp
Low oil pressure
EGT overtemp
Start failure
Acceleration failure
Failed sensors 
Internal failure

Question 12

How does the APU GEN power the DC Electrical system?

Answer 12

Through the Right Main 28vDC Bus

Question 13

The APU has a fully automatic fire detection and extinguishing system powered by?

Answer 13

The Right Essential 28vDC BUS

Question 14

If the APU Fire Detection Loop detects a fire, how long does it take between automatic shutdown and the release of the Halon from the fire bottle?

Answer 14

Approximately 7 seconds

Question 15

What lights would we see if the fire detection loop were to fail?

Answer 15

MASTER WARNING
CHECK FIRE DETECT warning light
Amber FAULT light on the APU Fire Protection Panel

Question 16

What lights come on with an APU fire test?

Answer 16

On the APU Fire Protection Panel (5):
White FUEL VALVE CLOSED light
EXTG pushbutton
White BTL ARM light
Red FIRE indication
Amber FAULT indication

On the APU PWR button (1):
Amber FAIL indication

On the Caution/Warning light panel (2):
Red CHECK FIRE DETECT warning light
Amber APU caution light

MASTER WARNING
MASTER CAUTION

Question 17

What lights would we see with an APU fire?

Answer 17

All of the same lights as the APU Fire Test, except for the FAULT light on the Fire Protection Panel. If the BTL ARM light does not extinguish after 7 seconds, press the EXTG pushbutton on the FPP.