ATA 49 - AUXILIARY POWER UNIT

• The APU is designed to operate throughout the entire flight envelope.

• APU speed must be below 7% before the starter motor is re-engaged-relight the APU on shut down procedure.

• The ECB starts an automatic emergency shutdown when and APU fire is found on ground.

• Any fluid that may accumulate in the APU COMPT (R/H of APU door) is delivered to a drain mast-emptied at 200 kts.

• The APU IGV (Inlet Guide Vane) actuator is operated by high-pressure fuel supplied from the Fuel Control Unit (FCU).

• The APU fuel pump runs as soon as the pump inlet pressure is lower than 21.8 psi (1.50 bar). It stops when the pressure is above 23.2 psi (1.60 bar).

• During starting, the ECB switches the ignition to ON between 0% and 60%. At 50% RPM starter is commanded off.

• A data memory module installed on the APU inlet plenum keeps and interchanges many parameters with the ECB: APU S/N, operating hours, time accumulated and shoot downs data.

• When the level s at the "ADD" mark 4.60 l (1.22 US gal), the APU can continue to operate for 10 hours maximum.

• If the temperature is too high or the oil pressure is too low the sensor or the switch transmits a signal to the ECB and starts the automatic APU shutdown sequence AIPIC

• Up to 20’000ft bleed air for the air conditioning and engine starting system & electrical power till cruise level (41000 ft)

• The ignition system is a dual system with two igniter plugs, which gives the constant high-energy ignition which ignites the fuel/air mixture in the combustion chamber.

• 3 consecutive start attempts are permitted without cooldown. After the third start attempt the starter motor must cool down for at least 60 minutes.

• For the manual drive of the APU main shaft, a manual drive shaft is installed on the front of the starter motor.

• Then the ECB controls and regulated fuel pressure from the Fuel Control Unit (FCU) operates the bleed control valve to the necessary position.

• If the BMC 1 finds a leak in the APU bleed-air ducts, while there is a Main Engine Start (MES) signal from the engines, it ignores the leak signal and commands the ECB to open the APU bleed load valve.

• In the cooling fan there is a Permanent Magnet Generator (PMG) installed, which supplies direct current voltage to the ECB. This used as an emergency power supply for the ECB. The PMG also provides back- up overspeed protection.

• Check plug for particles. If particles are larger than 0.15 mm (0.06 inch), replace the APU.

• APU Auto shut-down:

- Over-speed

- Over-temperature

- Low Oil Pressure (LOP)

- Under-speed

- High Oil Temperature (HOT)

• APU fuel is coming from L/H Wing Tank.

• APU fuel pump is controlled by APU MASTER SWITCH → ECB

ECB checks APU FUEL PRESS SWITCH and if fuel pressure in the line is less than 21.8 PSI it turns APU FUEL PUMP “ON”, then it opens LP FUEL VALVE letting fuel flowing to APU.

• ECB controls APU starting cycle and sends data to ECAM.

• APU electrical power has priority over APU bleed-air.

• APU starts at any altitude, provides electrical power at any altitude and provides bleed-air up to 20000 ft.

• The 2 APU doors have 7 latches.

• APU bleed-air comes from LOAD COMPRESSOR while APU electrical power comes from STARTER/GENERATOR.

• APU AVAIL LIGHT comes on as soon as APU N speed is above 95%.

• APU OIL FILTER has a by-pass valve monitored by a DELTA PRESSURE SWITCH in case of filter clogging.

• APU EXHAUST is connected to R/H APU compartment door.