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APU OPERATION
General
Operation of the APU is provided through the
APU control panel located on the cockpit cen-
ter pedestal, the APU Bleed S/I on the pres-
surization control panel, and the APU GEN S/I
on the electrical control panel (Figure 6-8).
Electronic Control Unit (ECU)
The electronic control unit (ECU) is a fully au-
tomatic, digital unit, located in the tailcone.
The ECU is the interface for receiving inputs
and sending the required output signals to
safely start, operate and shutdown the APU.
The following functions are controlled by the
ECU:
• Start sequence
• Acceleration timing
• On-speed governing
• Normal shutdown
• Fault detection and fault logging
• Connection to other aircraft subsystems
APU Starting System
When the APU MASTER S/I (Figure 6-8) is
pressed, the ECU power supply is activated and
initiates an internal test mode. The operator
must wait at least 10 seconds after pressing the
APU MASTER S/I before pressing the mo-
mentary START S/I. This allows the ECU to
complete the power-up and test modes.
F o l l ow i n g t h e B I T E t e s t , t h e A P U
START/STOP S/I on the cockpit panel is
p r e s s e d t o i n i t i a t e t h e s t a r t . T h e w h i t e
“ S TA RT ” c a p t i o n i s i l l u m i n a t e d i n t h e
switch/indicator by the ECU and remains on
for the entire start sequence.
6-7
FOR TRAINING PURPOSES ONLY
L E A R J E T 4 5
P I L O T T R A I N I N G M A N U A L
FlightSafety
international
I 0 0
APU
FAIL
START
RUN
ON
A
P
U
GEN AMPS
MASTER
START/STOP
FIRE
PUSH
FIRE
R MAIN
R GEN
L BATT
R BATT
APU GEN
OFF
OFF
ON
AVAIL
OFF
OFF
ON
DEPLOY
OFF
PAX
OXY/AUTO
PAX OXYGEN
OFF
L BLEED
ON
EMER PRESS
OFF
R BLEED
ON
HI FLOW
OFF
PACK
ON
APU BLEED
LDG ALT
DN
UP
ELECTRICAL CONTROL PANEL
PRESSURIZATION CONTROL PANEL
APU CONTROL PANEL
Figure 6-8. APU Controls