APU Flashcards
How is the APU intake flap opened? What happens if you press the START pb prior to flap opening?
APU master switch ON.
The APU computer (ECB- Electric control box) will not permit APU to start until flap is fully open.
What is the normal function of APU MASTER SW pb?
Controls electric power supply to APU and turns on the ECB.
Will APU shutdown with a LOW OIL LEVEL message?
No. APU may be started and operated, however maintenance is required within the next 10 hours of APU operation.
Will APU shutdown due to low oil pressure?
Yes. No message displayed, and ECB directs APU to automatically shutdown.
Where is APU fuel supplied from?
APU fuel supply line is directly connected to engine 1 feed line- normally supplied by left inner tank.
When does the APU DC fuel pump operate?
If there is no fuel pressure in engine 1 feed line when APU MASTER SW pb selected ON, ECB energises it. No flight deck indications.
*when engine 1 fuel line pressurises, ECB shuts down APU fuel pump.
What happens if FUEL LO PR appears on APU page?
APU automatically shuts down.
At what N% will ON light extinguish on APU START pb and AVAIL appear on pb and APU page?
95% N
On shutdown will the APU need to cool?
If bleed air was in use, APU will run for a cooling period of 60-120 seconds at 75%N.
When will APU automatically shutdown due to EGT?
EGT reaches redline. Amber line indicates 33 deg below max.
Will APU automatically shutdown if an APU fire is detected?
Inflight- No- flight crew must manually shutdown.
On ground- Yes- ECB will command an automatic shutdown and halon extinguisher automatically discharged.
What is the service ceiling of APU? What is the maximum altitude for start?
Ceiling- 39000ft.
Start- 25000ft.
What altitude is APU bleed air available up to?
22500ft.
What is the maximum pressure altitude for an APU ground start/operation?
14500ft.
What is the APU max N speed?
107 % N.
What is the APU starting and operating max EGT?
Starting- 1090
Operating- 675
What is the APU starter motor duty cycle?
3 attempts with 1 minute cooling, then 60 minute cooling.
How can cold soaking of APU compartment affect starting?
A start cannot be guaranteed if aircraft has been airborne above 8000ft for longer than 1.5hours.
Should APU start be attempted in emergency electrical configuration?
If fuel remains- YES
To recover cabin pressurization, additional electrical power and have bleed available for a starter-assisted relight, if necessary.
Each APU start attempt reduces flight time on batteries by about 3 and a half minutes. Total flight time on batteries is more than 30 min.
PR-AEP-ENG P 2/26
