APU Flashcards
APU
What is the altitude limitation for APU operation?
43100’ (max. certified ALT).
What two things are supplied by the APU?
• Electrical power (has priority over bleed air). • Bleed air.
How can the APU be started?
By the APU electrical start motor (powered by APU battery) or an air turbine starter.
What supplies the APU starter motor?
APU battery.
What supplies the APU inlet door?
Main battery.
Which type of start has priority ?
Air turbine starter has priority over electric start motor when there is sufficient bleed air duct pressure.
Can ground cart air be used to start the APU?
Yes.
Which AC fuel pump runs automatically to feed the APU?
L FWD AC fuel pump in the L main tank operates automatically (with AC power AVBL and APU selector in on position).
When does the starter engage and disengage?
Engages when the APU air inlet door reaches full open position. Disengages when APU reaches approx. 50%.
What will cause an APU autostart in flight?
If both AC transfer busses lose power.
How is the APU shutdown after an autostart?
By positioning APU selector to ON, then OFF
How is the cool down indicated?
EICAS message APU COOLDOWN displayed during cool down period (APU shuts down after cool down period).
When is the APU running in the unattended mode?
On GND W/ all engines shut down (in attended mode all other times).
What will cause an automatic shutdown in the attended mode?
• APU fire/inlet over temperature. • Overspeed/loss of overspeed protection. • High EGT. • Low oil pressure. • High oil temperature. • Generator oil filter approaching bypass. • Intake door failure. • APU controller failure. • Speed droop. • No combustion on start. • No acceleration on start.
Does the APU perform a cooldown during an automatic shutdown?
No
