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used only when the oil replenishment system does not function.
FUEL CONTROL AND INDICATION
The fuel system is a fully automatic electronic control system. The fuel control unit
provides metered fuel to 10 fuel injection nozzles regulated by signals received from
the FADEC.
During start the fuel system provides the correct amount of fuel to support combustion
and for smooth acceleration of the engine to full rated speed. Once on speed, fuel flow
is modulated as necessary to meet the demands of varying pneumatic and electrical
loads, while maintaining a constant speed.
AIRFRAME FUEL
Fuel is normally supplied to the APU from the right engine feed line, or from the left
engine feed line by opening the crossfeed shutoff valve. The examples below represent
the APU operation with DC and AC power applications. Please refer to Chapter 11,
FUEL SYSTEM for further information on the airframe fuel system operations.
4-10 For Training Purposes Only
Sept 04
P I LOT T R A I N I N G GU I D E
AUXILIARY POWER UNIT
P P P
P
P P
P
P
FUEL
AUX
22°C
APU
22°C
TOTAL FUEL
36O5OLBS
14975LBS
AUX
61OOLBS
14975LBS
FUEL USED
3OOLBS
LO PRESS
32°C 32°C
LO PRESS
P P P
P
P P
P
P
FUEL
AUX
22°C
APU
22°C
TOTAL FUEL
36O5OLBS
14975LBS
AUX
61OOLBS
14975LBS
FUEL USED
3OOLBS
LO PRESS
32°C 32°C
LO PRESS
P P P
P
P P
P
P P
P
FUEL
AUX
22°C
APU
22°C
TOTAL FUEL
384OOLBS
146OOLBS
AUX
92OOLBS
146OOLBS
FUEL USED
3OOLBS
LO PRESS
32°C
OLBS
32°C
LO PRESS
P P P
P
P P
P
P P
P
FUEL
AUX
22°C
APU
22°C
TOTAL FUEL
384OOLBS
146OOLBS
AUX
92OOLBS
146OOLBS
FUEL USED
3OOLBS
LO PRESS
32°C
OLBS
32°C
LO PRESS
GX_04_005
Auxiliary Pump
APU starting and no main engines running:
The right AUX pump supplies the APU through
the right engine feed line.
APU on-speed and no main engines running:
The right PRI pumps feed the APU
through the right engine feed line.
Crossfeed
Shutoff Valve Primary Pumps
Global Express
Global 5000
Global Express
Global 5000
For Training Purposes Only
Sept 04
4-11
P I LOT T R A I N I N G GU I D E
AUXILIARY POWER UNIT
IGNITION
The ignition system consists of a dual output ignition unit, two ignition leads and two
igniter plugs. There are two cycles of operation: BURST for starting (at 5%) and
MAINTENANCE for acceleration (duration of the start).
The ignition system is fully automatic and controlled by the FADEC. Ignition occurs
at 5% APU rpm.
During APU ground operation (nonessential mode) ignition is terminated at 50% rpm.
During flight (essential mode) ignition is terminated at 98% rpm.
Should a flameout occur during operation, ignition sequence will automatically start
through the “Auto Relight” function of the FADEC.
START SYSTEM
Operation of the starter is automatically controlled by the FADEC, through the APU
control switch. Starter operation begins by selecting the START position on the APU
control panel. At sea level, starter cutout occurs at 46%. At altitude, starter cutout may
be as high as 60% to ensure a positive start.
The starter is capable of an immediate restart on roll down when APU rpm is at or
below 7% rpm.
SPEED INDICATION
Two speed sensors provide indicated speed for on-speed control and overspeed APU
protection.
During operation, the FADEC monitors the input and should either sensor fail, there
will be an APU FAULT advisory message displayed on EICAS.
A failure of either sensor will not cause an APU protective shut down to occur.
However, a failure of both sensors will cause an APU protective shutdown both on
ground and in the air.
TEMPERATURE INDICATION
The EGT system consists of a single temperature sensing unit with two probes. The
probes provide redundant signals to the FADEC for fuel schedule trim, turbine
temperature monitoring, and Load Control Valve modulation. The APU is protected
from overtemperature during acceleration by protective features incorporated in the
FADEC.
Loss of one probe will not affect APU operation.
In the nonessential (ground) mode, failure of both probes will cause the FADEC to
　
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