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BATT
ON
ON
AVAIL
IN USE
AVAIL
IN USE
MIC HDPH
LAMP
TEST
APU
SHUT-OFF
GX_04_010
APU Compartment
Forward Bulkhead
APU Emergency
Shutoff Button
APU Compartment
Shutdown Button
4-20 For Training Purposes Only
Sept 04
P I LOT T R A I N I N G GU I D E
AUXILIARY POWER UNIT
PROTECTIVE SHUTDOWNS
The FADEC will automatically shut down the APU when any of the following are
detected:
SHUTDOWN CONDITIONS GROUND FLIGHT
NOTE: An X in one or both columns indicate when shutdown can or will occur.
FADEC Failure: Internal failure. x x
Inlet Door: Not in commanded position. x x
Loss Of Overspeed Protection: Loss of any combination of speed sensors,
FADEC overspeed circuitry or fuel solenoid that results in a loss of both overspeed
systems.
x x
Overspeed: APU speed greater than 106 percent. x x
Loss Of Speed: Loss of both APU speed signals. x x
Fire: Fire signal received by APU FADEC. x
DC Loss: Loss of DC power to the FADEC. x x
Slow Start: No crank, slow start, no acceleration, no flame or fall back (starter
cutout and subsequent drop below 25 percent) x x
High Oil temperature: Oil temperature limit exceeded. x
Low Oil Pressure: Low oil pressure condition detected. x
LOP Switch Fail: Low oil pressure switch failed. x
Loss Of Both EGT Sensors: Failure of both EGT thermocouples. x
Reverse Flow: APU inlet temperature exceeded. x
Underspeed: APU drops below 80 percent. x x
Overtemperature: EGT exceeds scheduled limits. x
For Training Purposes Only
Sept 04
4-21
P I LOT T R A I N I N G GU I D E
AUXILIARY POWER UNIT
SYSTEM OVERVIEW SCHEMATIC
PUSH
OFF/RESET
APU GEN
FAIL
OFF
APU BLEED
AUTO
OFF ON
BLEED / ANTI-ICE
LP
AIR
COND
HP
L
LP
HP 40
PSI
40
PSI
R
Load
Control
Valve
BLEED AIR/ANTI-ICE SYNOPTIC PAGE
APU BLEED
SELECTOR
GENERATOR
CONTROL
GENERATOR OUTPUT
TO BUS DISTRIBUTION
RPM
ON OFF
GENERATOR
CONTROL
UNIT
EGT
APU
ELECTRONIC
CONTROL
UNIT
GX_04_011
APU
4-22 For Training Purposes Only
Sept 04
P I LOT T R A I N I N G GU I D E
AUXILIARY POWER UNIT
ELECTRICAL POWER AND DISTRIBUTION
The electrical control of the APU consists of electrical sensing, starting and ignition,
and the electronic control system through the FADEC.
APU electrical power may be used in flight or on ground. Electrical power is extracted
from the APU in the form of horsepower that drives the APU generator, and may be
used to feed the airplane electrical power system.
Under high electrical load demands, the APU’s electrical load takes priority over
pneumatic load demands.
The APU generator load limit is 40 kVA.
For operations above 37,000 feet, if the APU is powering a bus, the associated
hydraulic pump must be selected off (due to the heavy load of the pump).
The FADEC is mounted remotely from the APU in a compact enclosure located in the
aft equipment bay.
The FADEC is powered up when the BATT MASTER switch is selected ON. The
BATT MASTER switch powers the airplane BATTERY BUS, which provides
electrical power to the FADEC.
The FADEC uses the APU acceleration rate to calculate when to de-energize the
starter motor and the ignition exciter. The values shown (START CONTROL
SCHEMATIC below) are the maximum speeds at which the starter motor and the
ignition exciter are permitted to operate.
START CONTROL SCHEMATIC
28 VOLT
DC
ELECTRONIC
CONTROL
UNIT
APU STARTER
MOTOR
APU IGNITION
EXCITER
DATA ACQUISITION
UNIT (DAU) #3
APU EGT AND
RPM INDICATIONS
ON EICAS STATUS
PAGE
50% (GROUND)
98% (AIR)
DE-ENERGIZED
5% RPM
ENERGIZED
0% RPM
ENERGIZED
46% - 60% RPM
DE-ENERGIZED
GX_04_012
APU
RUN
OFF START
For Training Purposes Only
Sept 04
4-23
P I LOT T R A I N I N G GU I D E
AUXILIARY POWER UNIT
The FADEC control outputs include fuel metering, arming and regulation of the LCV
and control of the SCV. It also performs protective shutdowns when the APU is not
within allowable operating limits.
A BITE capability of the FADEC tests components for serviceability and initiates the
start sequence. It also enables reliable fault isolation within the system.
FADEC INPUTS AND OUTPUTS
The following are input signals received by the FADEC:
　
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