APU System Flashcards
What is the primary and secondary function of the APU?
Provide electricity, and then bleed air
Maximum Operating Altitude of the APU
41,000ft
Maximum Altitude for Bleed Air extraction off the APU
25,000ft
Maximum Altitude to start the APU
37,000ft
What is the APU intake door used for?
To allow air to enter the APU compartment for combustion and cooling
What button opens the intake door for the APU in flight?
the START/STOP switchlight
What is the maximum airspeed if the position of the door is open or unknown in flight?
220 knots
What tank supplies the APU with fuel?
Left collector tank
What is the function and location of the APU Fuel Shut-Off Solenoid Valve?
It is located between the Fuel Control Unit and the spray nozzles, modulates the amount of fuel directed to the fuel nozzles, it closes to shut down the APU
What happens when you push the APU PWR FUEL switchlight?
- Activates the APU ECU
- Activates the APU Fuel Pump
- Opens the APU Fuel Shutoff Valve
- Activates the EICAS Displays
- Initiates the IN BITE
- Opens the APU Door
How is the APU cooled?
Through the APU eductor. On the ground, it creates a venturi effect which sucks the hot air out of the compartment. In flight, ram air pushes the air out.
At what RPM’s should the APU starter disengage?
Between 46% and 60%
What controls the APU ignition system?
A 24V battery
What is the power source for the APU ECU?
APU starter?
ECU is powered by the Main Battery Bus, and the starter is powered by the APU Battery Bus
What will happen if the APU EGT limit is reached?
The ECU will modulate the LCV towards closed to limit bleed air extraction, which in turn causes the EGT to decrease
