APU Flashcards
How many lights/items appear during an APU fire test?
- 2 Overhead / 4 Master Caution panel / 2 CAS
APU is guaranteed to start at or below
39,000’ (may start up to 43,000’)
What is the max operating altitude of the APU?
45,000’
APU Generator will come on when it has reached:
2 seconds after it has reached 99%
On APU Start, when does Isolation valve open?
1 minute after APU is online.
load control valve is inhibited OFF during APU start unless EGT before start >150°. There is no delay when airborne
If started in the air, the APU will remain in ESSENTIAL mode for how long after landing?
15 minutes
APU Essential and Nonessential modes depend upon which system
WOW
The APU surge control value operates at what altitude and above?
16,500 - to prevent high altitude compressor stall.
The bleed air augmentation valve opens at what altitude?
35,000’ and higher - allows 400°F bleed air into inlet
The Bleed Air Augmentation Valve delays APU start for
15 seconds to allow warm up
What temp range is APU oil tank heated to
+21°C to 43°C regardless of whether the APU is in use
Depressing the APU STOP switch cause the APU
to shut down by simulating overspeed
APU Starter limitations
3 start attempts, one hour cool down
What are the APU starter limitations when using Ext DC?
3 start attempts, separated by 15 minutes, then one hour cool down
How is an APU start manually aborted?
APU STOP, which triggers the 108% overspeed circuit resulting in an immediate shutdown.
The minimum fuel temp required prior to APU start
> -30°C
Min battery voltage for APU start
22 VDC
When is the APU air load control valve automatically inhibited OFF/how long?
During start, after start for 90 seconds
How is it determined that all parameters are acceptable for APU start?
APU Ready light
Will the APU start be inhibited with the absence of the READY light?
No, however the APU air inlet door must be verified open prior to start
Describe the normal APU shutdown - ground, air
Ground - Cooldown period is initiated, loads are shed within 2 sec. APU RPM decreases 1/2% for 60 seconds
Why is there a requirement for turn OFF the right battery for an in-flight APU start with one or both main generators powered?
Because both batteries combined with their chargers produce too much amperage (starter torque) and may ramp the APU starter past the APU start envelope
Is the APU electronic control unit still powered after the APU master switch is deselected?
Yes, for 5 minutes
Can the APU provide pressurization in flight?
No
If the APU is started on the ground and not shut down prior to takeoff, what mode will it be in flight?
Essential
If landing with the APU running, how long will it stay in essential mode?
15 minutes
The APU receives fuel from…
The motive flow line to the left fuel ejector in the left hopper
When will APU generator power the AC buses after start?
2 seconds after it reaches 99% - with APU GEN switch ON
At approx what RPM will the APU ECU close the external door during shutdown?
40%
At what point will the APU ECU close the inlet door if the pilot uses the MASTER switch to shut down the APU?
Immediately
When does the AFM allow the crew to run the APU inflight?
Four times Single Gen Failure Double Gen Failure Single Engine Failure Dual Engine Failure
When Checklist instructs.
When do you check the oil level?
Between 15 and 30 minutes after shutdown.
APU provides bleed air up to what altitude?
- 1,500 AGL for pressurization during a Bleeds-off takeoff
- Up to 30,000’, but current AFM limits use only allow for bleed air use up to 25,000’ for Main Engine Start in-flight.
When does the AFM allow the crew to run the APU inflight?
Four times Single Gen Failure Double Gen Failure Single Engine Failure Dual Engine Failure
When Checklist instructs.
