APU

Question 1

What is the electrical supply?

Answer 1

115V 40kVA up to 33,000’

Question 2

How is fuel supplied?

Answer 2

DC Power:

DC pump, right fuel tank

AC Power

AC fuel pump, right tank (no engine)

Ejector fuel pump, right tank (right engine running)

Ejector fuel pump + crossfeed valve, left tank (either engine)

Question 3

General System Description

Answer 3

Air Management System (AMS) controls bleed air for packs and engine start operations

Bleed for engines starts to 21,000’

Bleeds for a/c and pressurization to 15,000’

Question 4

Operation

Answer 4

Max starting altitude is 30,000’

Controlled through FADEC (via selector knob) or EMER OFF (guarded)

ON: Powers FADEC and opens fuel SOV; EICAS changes from OFF to APU indicators

START: Electronic start; APU > 95% electrical and bleeds available

OFF: Bleeds removed, 1 min cooldown, electical removed, shuts down (reselected ON cancels shutdown)

b) or via EMER STOP: Fuel shutoff valve closes

Question 5

What are the autoshutdown events?

Answer 5

Air:

Overspeed, underspeed, FADEC fault

Ground:

Air events + fire, EGT overtemp, high oil temp/low pressure, sensor fail