APU Flashcards
What is the APU starting altitude envelope?
-1000 to 20,000 ft
What degree does the APU air intake door open on the ground? in flight?
35 15
What does the Auxiliary Start Relay on the APU do?
acts as a holding relay until the APU reaches 50%, then it is de-energized
Fuel for the APU comes from where and how does it get there?
Gravity fed from Tank 2
How much fuel must be in tank 2 IOT feed the APU without turning the boost pumps on?
2000 lbs
What does external power supply power to?
LH/RH AC bus, essential AC bus, and main AC bus which in turn powers the avionics buses and all four regulated TRs
What is the reset position for the APU generator?
OFF on the external/APU switch
When the External power/APU switch is placed to APU, what does it power?
connects the APU generator to the essential AC bus
What is powered if the APU is the only source of power?
essential and main AC buses
When does the start light on the APU go out?
until the APU compressor reaches 50 percent rpm
An ESS DC BUS OVERLOAD ACAWS message may appear during APU starts. No maintenance is required unless what?
unless a TR and/or other bus fail ACAWS message also appear
The APU has to warm up for how long without a bleed air load?
1 minute
What is the starter duty cycle?
1 minute ON, 4 minutes OFF
How long is the APU door operation?
9-18 seconds
How long from APU start light to on speed?
35 seconds
Normal APU rpm
98-105 percent
Max APU rpm
110 percent
Normal APU EGT
260-680 C
Max APU EGT and for how long?
710 C for 3 seconds maximum
What is the general purpose of the APU?
supplies air for ground operation of the AC systems and for engine starting provides shaft power to drive a 40-kVA AC generator
When is the APU fuel and ignition circuits energized?
when APU oil pressure rises above approx. 4 psi
When does the APU automatically shut down?
APU speed exceeds 110% oil pressure is low tachometer fails
How is the APU maintained at a constant speed of 100%?
the speed-sensing governor controls it by regulating fuel flow into the combustion chamber
What supplies APU starting control power?
isolated DC bus
What supplies power to the APU start motor?
the essential DC bus (if the essential DC bus is powered) and the utility battery
What should you do if the APU does not light off during ground start in extreme cold weather?
preheat the APU with an external source of heat prior to second start attempt
What occurs when the APU oil subsystem senses low oil pressure?
APU automatically shuts down
