Apu Flashcards
What are the start sources of the APU and which do we normally use?
APU battery: Normal
T/R (util bus 4 powered)
Can the APU be operated in flight
Yes
Operated to 20,000ft
Only start on the ground
APU electrical or Bleed available in flight?
Electrical - NO
Bleed - yes, one pack, 15,000ft
What components powered by APU battery?
APU controller
DC Fuel Pump
APU inlet door
DC electrical starter
APU fire detection system
What components are powered by main battery?
APU fuel valve
Standby power APU controller
(Note: during APU battery start, DC electrical starter is powered by APU battery why all other APU functions are powered by main battery
What powers the APU starter during the battery start sequence
No util bus 4 then 24V APU batt (norm)
APU start T/R whenever util bus 4 is powered (either external or internal AC power source through synchronous bus)
T/R overheat with start source in T/R
Transferred to battery and start continues
T/R failure besides overheat
- Does not provide automatic switching
- moving APU start source to BATTERY removes T/R from circuit and allows start
When does EICAS memo message APU running display?
APU RPM >95%
Describe the APU shutdown sequence
Select APU selector to - OFF
- closes APU bleed valve
- initiates 60 sec cool down
- end of cool down APU shuts off
What would happen if the battery switch is positioned to off prior to completion of the APU cooldown period?
APU shuts down immediately
How long should you wait before turning off the battery after the APU selector is rotated to OFF why?
2 minutes
Fire Detection capability available
What would cause the APU to shut down automatically!
Limit exceedance
Fire detected
