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APU

Also from: Auxiliary Power Unit

ATA 49 (Airborne Auxiliary Power)

The Garret APU is a single spool and has 2 compressors. It has its own FADEC known as the ECB that controls all operations.

Components

• 1× ECB

Controls

MASTER SW

When pressed:

• ON light illuminates
• ECAM APU page is automatically displayed
• FLAP OPEN indication appears when the APU air inlet is fully open (not required before pushing the START pb)

The FAULT light provides a cross check of the ECAM in case of a fault.

START

When pressed:

• ON light illuminates
• at 95% N the ON light extinguishes and the AVAIL light illuminates

APU BLEED

When pressed:

• ON light illuminates
• APU bleed valve opens

Bleed air

APU bleed air is produced from a dedicated load compressor which supplies about 30psi (increases for engine start), varied by inlet guide vanes. The APU bleed air duct is connected to the left side of the pneumatic duct. It is controlled through an APU bleed valve which acts as a shutoff valve. APU bleed air should not be used if ground air is connected. With the APU bleed air on, the memo APU BLEED is displayed on the E/WD.

The bleed valve is closed on climb at 25,000' and opened on descent at 23,000'.

Fuel

The APU uses fuel from the #1 collector cell (left hand inner tank). APU feed is from the trim pipe during an aft transfer above FL255 and during refuelling of the trim tank. It is fed from the trim tank above FL 255 and during a forward transfer.

Feed From	Phase	Fwd APU Pump	Aft APU Pump
left inner tank	ground operation, climb to FL255, cruise above FL255 with trim tank empty, descent and landing
trim pipe	refuel of the trim tank, above FL255 aft transfer
trim tank	above FL255 with no transfer, forward transfer

Preflight

Check that the APU fire extinguisher overpressure red disc is in place (external, at the rear of the aircraft).

Shutdown

The shutdown is performed by pushing the MASTER SW pb. There is a 2 minute cool down period before the APU shuts down. During this time the START sw AVAIL light remains illuminated, and by pushing the MASTER SW again, the shutdown process can be stopped. Emergency shutdowns without the cooldown period can be performed with the APU fire pb in the cockpit, as well as on the refuel/defuel panel and the external power panel.

	ground	flight
fire (with auto extinguishing)
	engines off	engines on
all faults
critical faults - overspeed, ECB failure

Other faults include underspeed/overspeed, start abort, low/high oil temperature, and DC power interruption.

Categories: Airbus A330 | APU | Pneumatic System | Fuel System