APU Flashcards
What does the APU supply?
28v DC power to main feeder bus. (Same as engine starter-gen)
Bleed air to ECS
What is the APU fuel consumption?
200 lbs/ hour
What are the APU restrictions?
Ground use only
Can’t start during fueling operations
Can’t be operated during gravity fueling
Gen on first before bleed air
Must not be operated unattended with passengers on board
What happens if you forget the APU on for takeoff?
Shuts off automatically on liftoff.
Can the APU bleed air be on with engine bleeds selected on?
What about a ground air cart?
No - desensitized by WOW
Yes
Where does the APU get it’s fuel supply from?
Left tank
How long should you wait after starting the APU before you turn on the bleed air?
3-5 minutes
What are the APU temperature limits?
….with inlet louveres?
-54°C to 50°C or ISA +35°C
21°C with inlet louvers installed.
APU starting limits
1 minute on, 5 minutes off
1 minute on, 30 minutes off and maintenance action required.
What is a nice trick to increase success rate in starting the APU in winter?
Press the self test then wait 3-5 minutes before pressing the start button.
What precaution must be taken when using external power to ensure that the APU GEN comes on line in the event of GPU failure?
APU GEN needs to be reset or else it doesn’t automatically kick in once GPU is offline. Therefore just cycle the APU GEN off then on after start up.
If pressing the APU PWR button does not shut down the APU, what can be done to shut down the APU?
Press the FIRE TEST button on the Fire Protection Panel (APU section is on the left part of FPP).
What is the purpose of the APU FADEC?
It monitors normal operation, controls the start and responds to malfunctions. It also supplies fuel for starting, acceleration and speed regulation.
When will the APU fuel valve close? (6)
PWR button pushed while running.
APU fire test switch pressed.
A fire is sensed in the tail cone.
Aircraft gets airborne while APU is running.
Illumination of GEN OVHT light.
APU shuts down due to a Fault detected by the FADEC.
What is the maximum temperature you can start the APU if the louvers are on?
21 Degrees Celsius.
There are two round openings on the bottom fuselage in front of the APU access doors. What are they for?
Composite duct inlet is the one on the left and it provides positive airflow ventilation to keep the APU compartment cool. The other is to provide cooling for the starter-gen.
Describe the start sequence of the APU.
Starter cranks till 50% rpm. The start segment extinguishes and at 95% +3 seconds, the gen becomes available.
How do you verify the voltage of the APU gen?
Check main busses on electrical page.
When shutting down the APU, how long do you need to wait to hit the PWR button after shutting bleed air off?
20 seconds.
When the APU bleed air is operating, how is the cabin prevented from pressurizing?
Pushing the bleed air button automatically opens the rear safety outflow valve.
What happens if EGT exceeds limits due to high electrical load?
APU prioritizes the GEN, so it removes bleed air in order to take load off of the compressor.
When does the APU fire bottle fire after an APU fire?
7 seconds.
When must the APU be preheated?
-35 C or colder for more than one hour.
If you fly in temps -35C or cooler for more than an hour and you land in temps below -35C.
If the APU fails, how long is a start inhibited for?
2 minutes.
