APU Flashcards
Max APU starting ALT
30,000 ft
Mas APU operating ALT
33,000 ft
What happens to PACKS during engine start?
They turn off so APU pneumatics can dedicate its supply to engine start
Bleed air for air conditioning ALT
15,000 ft
Bleed air for engine start ALT
21,000 ft
Max ALT for APU electrical supply
Same as max APU operating altitude, 33,000 ft
What tank supplies fuel to the APU?
Fuel is supplied from the ejector pump in the wing tank 2
How is the APU fueled if the engine 2 is turned off?
The AC fuel pump is activated to provide fuel, or the AC pump in the wing tank 1 can provide fuel iffy the crossfeed vale is open
Fuel source priority for APU
-ENG 2 Ejector Pump
-AC Pump
-DC Pump
What powers the APU STARTER?
AC system, DC GPU, Battery 2
APU STARTER Limits
1st & 2nd Cycle………….60 secs ON, 60 secs OFF
3rd Cycle…………………..60 secs ON, 5 min OFF
Ignition cycle
Ground Start- ignition begins ate 6%, then FADEC- provides fuel
In Flight- ignition between 7 and 17%
The FADEC commands starter cutout at around 50%
3 seconds after APU reaches 95%, both electrical and pneumatic power are available
If the APU does not reach proper speed or acceleration rate within starting cycle time, the APU will automatically shutdown
When does the APU have bleed supply priority?
-Airplane on ground
- opposite engine bleed pressure is below min for engine start
- Ground speed below 50kts
-Xbleed valve operating normally
Is it necessary to turn off packs for engine start?
No. The APU supplies pneumatic air to the eng starters and pack flow valves automatically close.
APU cool down time
1 minute
