APU Flashcards
Describe the APU
Gas turbine engine, located in the airplane tailcone, provides pneumatic and electrical AC power
For what purposes APU bleed air can be used?
1) Engine starting
2) ECS PACKS supply
APU generator voltage
115 V (40 kVA)
APU engine
APS 2300
How is the APU controlled and monitored?
By its own FADEC
APU fuel supply
Only DC power — DC PUMP (RW TANK)
DC+AC power (ENG NOT RUNNING) — AC PUMP
ENG IS RUNNING — ejector pump (RW TANK or LW TANK via X-FEED)
APU altitude limitations
AC power <33000 ft
Bleed air for engine start <21000 ft
Bleed air for ECS <15000 ft
MAX APU START ALT — 30000 ft
APU OFF -> ON
1) FADEC POWER — ON
2) APU FUEL SHUTOFF VALVE — OPEN
3) EICAS “OFF” —> speed & EGT
Wait ___ seconds before ON —> START
30
What will happen if APU doesn’t reach proper speed or acceleration rate within starting time?
APU will automatically shut down
Difference between normal and emergency APU shutdown?
Normal — 1-2 min of cooldown then spooldown, then EICAS APU SHUTTING DOWN DISAPPEARS
Emergency — fuel shutoff valve closes with no cooldown period
White and red bars on the APU EMER STOP
White bar — APU EMER STOP
Red bar — APU FIRE
WHITE/RED BAR on EMER STOP
White — APU EMER STOP
Red — APU FIRE
When electrical and pneumatic power becomes available?
3 sec after 95% RPM
APU SHUTDOWN CYCLE
1) PNEUMATIC — immediately remove
2) ELECTRICAL:
APU is the NOT only source — immediately remove
APU is the ONLY source — until the end of shutdown process
