APU Flashcards
Fuel to start and operate the APU comes from ?
The left side manifold when the AC fuel pumps are operating.
The APU fuel boost pump is (blank) operated to ensure ?
DC operated to ensure positive fuel pressure to the APU fuel control unit
When does the APU fuel boost pump operate ?
It operates during start and operation automatically when the APU fuel control unit senses low fuel pressure
When does the APU fuel boost pump turn off
The APU automatically shuts off when the an AC fuel pump pressurizes the fuel manifold
If the AC and DC fuel pump are not operating how does the APU get fuel
If the AC and DC fuel pump are not operating fuel is suction fed from the no.1 tank.
APU engine air routes from where?
An automatically operated air inlet door located on the right side of the fuselage.
How is the APU cooled?
Air for APU cooling enters through a cooling air inlet above the APU exhaust outlet. This air circulates through the APU compartment, passes through the oil cooler and vents through the exhaust outlet.
Requirements to start the APU
- APU fire switch on the overheat/fire panel must be In
- APU fire control handle on the APU ground control panel must be in
- Battery switch must be on
- Electrically power from the #1 AC transfer bus or the battery bus is used to start the APU
APU start sequence
APU switch to start > initiates opening of the air inlet door > When APU inlet door full open start sequence begins > Once APU reaches proper speed, ignition / fuel provided > When the APU is ready to accept bleed air / electrical load the APU GEN OFF BUS light illuminates
How long can it take for the APU to start ?
120 seconds
automatic shutdown protection of the APU occurs if ?
If EGT is exceeded, overspeed conditions, low oil pressure, high oil temp, APU fire, fuel control unit failure
Moving the APU switch to OFF begins what sequence for shutdown
trips the APU gen > closes the bleed air valve > extinguishes the APU GEN OFF BUS light > shutdown occurs after 60 seconds > when the APU speed decreases the fuel valve and inlet door close > if the fuel valve does not close the FAULT light will illuminate