A320 APU Questions

When starting the APU, the FUEL LO PR indication appears amber when an APU fuel low pressure is detected.

• True
• False

Explanation: Correct. On the APU system display, the FUEL LO PR indication is shown in amber when APU fuel pressure gets low.

APU - Controls & Indicators (system display page)

When the APU MASTER SW is selected ON:

• The APU computer automatically completes a self-test, opens the air intake flap and supplies fuel pressure.
• The APU computer automatically starts the APU.
• Connects the APU generator to the aircraft electrical system.
• The APU door opens.

Explanation: Selecting MASTER SW ON energizes the ECB, which runs a power-up self-test, opens the air intake flap, opens the fuel isolation valve, and runs the fuel pump if needed. It does not start the APU by itself — that's the separate START pushbutton.

APU - Controls & Indicators (MASTER SW panel)

Will the APU bleed valve close automatically during climb? Will it reopen during descent?

• Yes
• No

Explanation: No. There's no automatic climb/descent cycling of the APU bleed valve — it closes automatically only for specific faults (leak detection, overpressure, etc.) or when the aircraft is above the applicable APU bleed altitude limit, and it doesn't reopen on its own just because the aircraft descends.

APU Limitations - Operational Envelope

The APU MASTER SW FAULT light will illuminate:

• When APU low oil pressure is detected.
• When an automatic shutdown of the APU occurs.
• For an APU overheat or APU fire.
• If the batteries are selected OFF while the APU is operating.

Explanation: The FAULT light comes on (with an ECAM caution) whenever an automatic APU shutdown occurs — low oil pressure, fire, DC power loss, overspeed, etc. are all individual items on that automatic-shutdown trigger list, but the light itself is tied to the shutdown event in general, not any single cause.

APU - Controls & Indicators (MASTER SW panel)

What are some of the causes for an APU automatic shutdown?

• Fire (on ground only), EGT overtemperature, No acceleration, low oil pressure.
• Fire (on ground only), EGT overtemperature, Underspeed, Overspeed, low oil pressure, high oil pressure
• Fire (on ground only), EGT overtemperature, Reverse flow, Overspeed, low oil pressure, high oil pressure
• Fire (on ground only), underspeed, overspeed, EGT overtemperature, Reverse flow, Low oil pressure, DC power loss.

Explanation: All of the listed items — ground-only fire, underspeed, overspeed, EGT overtemperature, reverse flow, low oil pressure, and DC power loss — are genuine automatic APU shutdown triggers.

APU - Controls & Indicators (MASTER SW panel)

The LOW OIL LEVEL advisory pulses in \_\_\_\_ if the APU oil quantity approaches its minimum value.

• Amber
• White
• Red
• Green

Explanation: This is a low-priority advisory, not a caution, so it doesn't use amber. On this aircraft's SD pages, values approaching a minimum advisory threshold (this applies to oil-quantity advisories generally, not just the APU) are shown by having the reading pulse in green rather than switching to amber.

APU - Controls & Indicators (system display page)

A FLAP OPEN indication is displayed in amber when the APU air inlet flaps is fully open

• True
• False

Explanation: This is false. FLAP OPEN is displayed in green when the APU air intake flap is fully open — that's the normal state, not a caution. It only becomes an advisory if the flap is still not fully closed a few minutes after the MASTER SW is turned off.

APU - Controls & Indicators (system display page)

With battery power only, what would an APU fire test look like?

• APU FIRE pb illuminated and SQUIB + DISCH lights illuminated
• APU FIRE pb illuminated
• SQUIB + DISCH lights illuminated

Explanation: On battery power alone, the fire test still works fully: the APU FIRE pushbutton lights up red, and both the SQUIB and DISCH lights come on.

Fire Protection - Engines and APU - Controls & Indicators