APU Flashcards
APU
On the ground ‐ It supplies bleed air for
starting the engines and for the air conditioning system ‐ It supplies electrical power to the electrical system.
During takeoff ‐ It supplies
bleed air for air conditioning (for example, when optimum aircraft performance is required).
In flight ‐ It backs up
the electrical system ‐ It backs up the air conditioning ‐ It can be used to start the engines.
The APU may obtain power for starting from
the aircraft’s batteries or normal electrical system, or from ground service.
The Electronic Control Box (ECB) is a full-authority digital electronic controller that performs the bulk of the APU system logic for all modes of engine operation, such as :
‐ Sequences the start and monitors it. ‐ Monitors speed and temperature. ‐ Monitors bleed air. ‐ Sequences the shutdown. ‐ Controls the automatic shutdown
The ECB controls the electric starter. The starter engages if
the air intake is fully open and the MASTER SW and the START pushbutton are ON.
Fuel for APU is fed by
Left tank
If pressure is not available (batteries only or pumps off) the APU FUEL PUMP
starts automatically. The ECB controls the fuel flow
For emergency shutdown :
‐ the flight crew can push the APU FIRE handle, or ‐ the ground crew can push the APU SHUT OFF pushbutton on the interphone panel under the nose fuselage.
In case of fire in the APU compartment :
‐ APU fire warnings operate in the cockpit. ‐ A horn in the nose gear bay sounds. ‐ The AVAIL light goes out. ‐ The FAULT light in the MASTER SW lights up. ‐ The APU shuts down. ‐ The APU fire extinguisher discharges.
Manual shutdown sequence.
‐ The ON light on the MASTER SW pb-sw, and the AVAIL light on the START pb go out. ‐ If the aircraft was using APU bleed air, the APU keeps running for a cooling period of 60 to 120 s. ‐ At 7 % the air inlet flap closes.
Blue START pb:
Blue ON light comes on.
‐ When the flap is completely open, the APU starter is energized. ‐ 1.5 s after the starter is energized, the ignition is turned ON. ‐ When N = 55 %. The APU starter is de-energized. The ignition is turned off. ‐ 2 s after N reached 95 %, or when N is above 99.5 %: The ON light on the START pb goes out. The APU may now supply bleed air and electrical power to the aircraft systems. ‐ 10 s later, the APU page disappears from the ECAM display.
APU ECAM
AVAIL:
Displayed in green when APU N is above 99.5 % or 2 s after N is above 95 %
Maximum EGT during start:
982 °C. Maximum EGT with APU running: ‐ 682 °C during at least 5 s. ‐ or, 700 °C to 742 °C depending on the ambient temperature.
