APU Flashcards
Max load on APU gen to 30,000ft
400A continuous
600A for 2 minutes
800A for 5 seconds
Max alt for APU start
30,000ft
Max alt for APU operation
37,000ft
Max tailwind for APU start
34kts
Max rotor speed
108%
Max EGT for start
884° but 10 sec at 925° above 25,000
Max EGT continuous
680°
APU start limits
1 min between 3 consecutive events
30 min after 3rd
What is the APU start sequence?
FADEC sends request to BAT2, which powers the APU starter. Ignition at 3% N1, STARTER deenergised at 70% and at 95% PLUS 7 seconds the APU can carry electrical loads.
When would the APU auto shutdown in the air and on the ground?
Overspeed/Underspeed, data loss, FADEC fail, failure to start or reach self sustaining speed
When would the APU shutdown on the ground and 30s after landing?
High EGT, High Ts and Ps.
Fire on ground - after 10 seconds
What happens when the APU MASTER is set to OFF?
De energises FADEC, closes APU fuel valve, below 10% N1 APU is shutdown
What happens if the APU FUEL shutoff is pressed? (+fire button pushed)
Stop request sent to FADEC, to signal ESU to stop, fuel valve closed. (+discharges extinguisher)
Where are normal APU indications shown?
EICAS
What controls the APU?
The Electronic Sequence Unit (ESU - a FADEC)
