This document provides information about an aircraft's Auxiliary Power Unit (APU). It details the APU's operating limits at different altitudes and with different numbers of air conditioning packs operating. It also summarizes the APU's functions in providing pneumatic and electrical power independently of external sources. Finally, it describes the various controls and indicators for monitoring and operating the APU that are located on the aircraft's overhead panel, fire panel, and external power panel.

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ALTITUDE (Ft)
20 000
39 000
15 000
25 000
APU BLEED
AIR
WITH
2 PACKS
OPERATING
With both air conditioning packs on,
the use of the APU for bleed air is
limited to 15000 Ft maximum.
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ALTITUDE (Ft)
20 000
39 000
15 000
25 000
APU BLEED
AIR
WITH 1 PACK
OPERATING
APU BLEED
AIR
WITH
2 PACKS
OPERATING
With only one pack on, the use of
the APU for bleed air is limited to
20000Ft maximum.
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ALTITUDE (Ft)
20 000
39 000
15 000
25 000
APU BATTERY
RESTART LIMIT
APU BLEED
AIR
WITH 1 PACK
OPERATING
APU BLEED
AIR
WITH
2 PACKS
OPERATING
31 000
The APU can be started using
batteries up to 25 000 Ft.
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ALTITUDE (Ft)
20 000
39 000
15 000
25 000
APU BATTERY
RESTART LIMIT
APU BLEED
AIR
WITH 1 PACK
OPERATING
APU BLEED
AIR
WITH
2 PACKS
OPERATING
31 000
RECOMMENDED
LIMIT FOR START
The recommended maximum
altitude for APU start is 31000 Ft.
This is not a limit however.
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ALTITUDE (Ft)
20 000
39 100
15 000
25 000
APU BATTERY
RESTART LIMIT
APU BLEED
AIR
WITH 1 PACK
OPERATING
APU BLEED
AIR
WITH
2 PACKS
OPERATING
31 000
RECOMMENDED
LIMIT FOR START
APU OPERATION
AND RESTART
LIMIT
APU ELEC
POWER
You can start the APU all the way to
the max ceiling of the aircraft, 39100 Ft.
Electrical power from the APU can
be used all the way to the max ceiling
of the aircraft.
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The Auxiliary Power Unit (APU),
is located in the unpressurized tail
cone.
It is a self contained unit which
can make the aircraft independent
of external pneumatic and
electrical power sources.
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The APU may be started using :
• the aircraft batteries,
• an external power source,
• or the normal aircraft AC power.
BAT 2
BAT 1
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The APU has an air
intake flap which, when it is
open, ducts external air to
its compressor inlet.
ENGINE START /
AIR COND
A/C ELECTRICAL
SYSTEM
APU GEN
BLEED
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ENGINE START /
AIR COND
A/C ELECTRICAL
SYSTEM
APU GEN
BLEED
MEU

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In the cockpit you
can monitor the
following APU
parameters on the
ECAM APU page :
• EGT and
compressor
speed
• APU bleed
• APU generator
• Flap position
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The various controls for the
APU are located on the overhead
panel.
The APU MASTER and START
pb sw are located on the APU
control panel.
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APU fire controls are located on the
FIRE panel.
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The APU BLEED switch is located
on the AIR COND panel; it controls
the APU bleed system, including the
automatic function of the
CROSSBLEED switch.
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The APU GEN switch is located on the ELEC panel.
In the normal “lights out” position, the generator is
automatically controlled according to the electrical
priority schedule. When deselected, the switch turns
the APU generator OFF.
The APU generator is activated by SWITCHING OFF
other power supplies. The electrical priority is: (1) any
engine driven generator (2) external power (3) the APU
(4) the other engine driven generator.

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There is also an APU
SHUT OFF pb and an
associated APU FIRE
warning light located on
the external power panel.
This panel is located in
the nose gear bay.
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LIST OF SUBJECTS
APU Limits
System Description
ECAM page
Controls & Indicators
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