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9. APU

9.1. Limitations

The APU may be started with DC from the batteries or with AC. The APU panel is located at the bottom centre of the overhead panel. External APU controls are located on the external power panel in the nose gear bay.

To start the APU, first press the master switch button, then the start button. The start sequence begins when the APU inlet flap is fully open.

To shut down the APU, turn off the master switch. If the APU bleed has been used, the shutdown sequence incorporates a delay of between 60 and 120 seconds before shutting down. As long as the AVAIL light is still displayed, the shut down sequence can be cancelled by turning the master switch back on. If APU bleed has not been used, the shutdown is immediate.

The APU control is completely automatic. Auto-shutdown is available whenever the APU is running. Automatic deployment of the APU extinguisher is also available on the ground. APU emergency shutdown is initiated by pressing the APU fire button or by pressing the APU SHUT OFF button on the external panel. An APU fire in flight will show the APU FIRE procedure on the ECAM, followed by the APU EMER SHUT procedure. On the ground, a fire will cause the APU AUTO SHUT DOWN procedure to be shown after the APU fire procedure.

The LOW OIL LEVEL on the ECAM indicates that the APU can only be used for a further 10 hours before maintenance is required. The amber FUEL LOW PR indication occurs during start if fuel pressure is low. It is only an advisory.

9.1. Limitations

Table 2. APU limitations
APU bleed air with 2 packs15,000ft
APU bleed air with 1 pack22,500ft
Battery restart limit25,000ft
Operation and restart ceiling39,000ft
APU elec power39,000ft