APU Flashcards
What are the start sources for the APU, and which one do we normally use?
APU battery power (24v) - normal position
TR - transforms AC power from utility bus 4 to DC for APU start
Can the APU be operated in flight?
Yes, up to 20,000’ but not started in flight
Is electrical power available from the APU in flight?
How about APU bleed air?
No elec power available in flight.
Bleed air available up to 15,000’
What APU components are powered by the APU battery?
APU inlet door, APU controller, DC fuel pump, and APU fire detection system
What APU components are powered by the main battery?
APU fire extinguisher, APU fuel valve, and standby power for the APU controller
What powers the APU starter during a battery start sequence?
APU Battery - all other APU components powered by main battery while APU starter engaged
What happens if the TR should overheat with the start source in TR?
starting power transferred to APU Batt, any further start attempts with TR inhibited
How does a TR failure affect APU starting?
does not auto-switch to APU batt (in comparison to overheat) - must move start source to APU Batt manually, which removes TR from starting circuit
When does EICAS memo message APU RUNNING display?
95% N1
Describe the APU shutdown sequence
APU selector rotated OFF
- begins shutdown cycle by closing APU bleed air valve
- APU continues running unloaded for 60 sec cooldown period
- APU shuts down
What would happen if the battery switch is positioned OFF prior to completion of the APU shutdown cooldown period?
APU shuts down immediately
How long should you wait before turning the battery switch OFF after the APU selector is rotated to OFF, and why?
2 mins, to ensure fire detection capability
What would cause the APU to shut down automatically?
fire detected or limit exceeded
