APU Flashcards
Max altitude for APU starting?
37,000 ft
What will happen if APU air is selected on immediately after APU start?
The APU air will turn on 90 second later
Will the APU start if the READY light is not illuminated?
If the ECU BIT test did not pass, APU start in not inhibited with the absence of READY light. If the crew deems that time is critical, the option of proceeding with APU start is still available. APU air inlet door must be verified open prior to attempting start.
What altitude is the 36-150 APU designed to operate and produce electrical power?
37,000 ft
Normal shutdown of the APU is accomplished by pushing what switch?
APU stop switch
Selecting what switch to the OFF position will close the APU fuel shutoff valve immediately?
APU master switch
Prior to starting the APU, how can the position of the right engine lower cowl door be checked?
Visually or by using the 2/3rd “Doors” Synoptic page
If necessary, how can the batteries be warmed most effectively prior to APU start?
Use an external AC power cart to charge and warm the batteries
What is the minimum acceptable battery voltage prior to an APU start?
22V
When is the APU air load control valve automatically inhibited OFF?
During APU start, and after APU start for 90 seconds
How is it determined that all parameters are acceptable for APU start?
The APU “READY” light will be illuminated
After APU start, when will the APU generator automatically power the electrical buses?
Four seconds after the APU achieves 95% RPM (assuming that the APU GEN switch is already in the normal ON position)
How is an APU start manually aborted, such as during a hung start?
Depress the APU STOP switch, which triggers the 108% overspeed circuit, resulting in an immediate start abort
How long are the APU RPM and EGT indications displayed after shutting down the APU?
For 5 minutes after the APU RPM is less than 5% and the APU MASTER switch is selected OFF (provided the APU ECU has a source of power)
What are the limitations for starting the APU with an external DC power cart?
Wait 15 minutes between start attempts
Would an APU FIRE cause the APU to shutdown in-flight or on the ground?
Both on the ground and in-flight
Describe a normal APU shutdown.
Once the STOP switch is pressed, the ECU shuts down the APU by generating and overspeed signal to shut off fuel to the APU. The air inlet door is fully closed only after the APU rpm degrades below 35%.
At what point will the APU ECU close the inlet door when the MASTER switch is used to shut down the APU?
It will close immediately
Is the APU ECU still powered after the APU master switch is deselected?
Yes, for 5 minutes
What is the rating of the APU generator, and is it interchangeable with the main generators?
40 kVA, it is not interchangeable with the engine IDGs
Can the APU provide pressurization in flight?
No
If an APU start attempt on battery power fails, how long a wait is required in order to try a second attempt?
Waiting is required after it fails a third attempt, then a 1 hour wait is required
If an APU start attempt on external DC power fails, how long a wait is required in order to try a second attempt?
15 minutes
If the APU was started on the ground, what mode will it be in flight?
Essential mode
The APU will be in what mode if the master switch is placed ON in flight, but it is not actually started until on the ground?
Essential mode
If landing with the APU running, how long will it stay in the essential mode?
15 minutes
Where does the APU receive its fuel?
From the left boost pumps and tank. If it is necessary to use the right tank, the crossflow can be opened and right boost pressure used.
What is the APU generator load limit when operating during flight?
The APU generator can deliver 100% electrical power (40 kVA) on the ground or in flight from sea level to 37,000 ft.
APU generator loading will be limited to 85% between 30,000 - 37,000 ft at speeds greater than Mach .85
