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The ECU activates the firewall fuel solenoid
and the right standby boost pump, a white “R
STBY PUMP ON” CAS is posted, and “ON”
is illuminated on the R STBY S/I.
At 50% rpm, the starter is cutout, backed up
by a terminate signal from the ECU at 60%
rpm.
When the APU reaches 95% operating rpm,
“START” extinguishes and “RUN” illumi-
nates (green) on the APU START/STOP S/I.
The green “AVAIL” light illuminates on the
APU GEN S/I, and a white “APU AVAIL-
ABLE” CAS message is posted. It is normal
to have a slight delay (less than 2 seconds) be-
tween illumination of the “RUN” and the green
APU GEN “AVAIL” light on the ECP.
The GEN AMPS window displays the gener-
ator load being extracted from the APU
starter/generator. During start, it indicates
zero. When APU generator output is com-
manded, the display shows the actual load
being supplied. Maximum load indication is
500 amps and is frozen at 500 amps until the
load drops below this value. APU generator
output (amps) is also displayed on the EICAS
electrical schematic page. The internal light-
ing of the generator amps window is con-
trolled through the left (pilot’s) instrument
light switch.
Bleed-Air Operation
The pneumatic output of the APU is controlled
by a Bleed Air Valve (BAV) located between
the compressor and combustion sections of
the APU. When opened, a portion of the com-
pressor discharge air is diverted to the air-
craft environmental control system.
When the APU is at full operating speed (green
“RUN” illuminated) depressing the “APU
BLEED” S/I on the pressurization control
panel opens the BAV allowing bleed air to the
aircraft pneumatic system (Figure 6-9). The
APU BLEED S/I will show a white “ON” in-
dication. After depressing the APU Bleed S/I
there is a delay of approximately 10 seconds
before the white “ON” is illuminated in the S/I.
Additionally, to allow APU bleed air into the
cabin and cockpit, the PACK S/I must be se-
lected on. The conditioning and distribution
of APU bleed air is the same as engine bleed
air as described in the Air Conditioning chap-
ter of this manual.
APU bleed air output is regulated by sensing
the APU EGT and inlet air temperature. As
pneumatic load increases, additional fuel flow
is commanded by the ECU. If the APU EGT
exceeds 649° C (1200° F), the ECU closes the
BAV to prevent an overtemperature condition.
The ECU will also close the BAV if a cockpit
or cabin duct overheat condition is detected.
The APU BLEED S/I is extinguished with
these overheat conditions, but can be reset
once the overtemperature condition is removed
or the APU is shutdown and restarted. Do not
set cockpit and cabin temperature selectors
above the 12 o’clock position when using APU
bleed air for heat.
The aircraft main bleed air leak detection sys-
tem loops extend to include coverage of the
APU ducting. If a bleed air leak is detected,
the APU is immediately shutdown by the ECU.
The APU BLEED S/I must be selected “OFF”
when conducting the anti-ice check prior to
takeoff.
Electrical Load
When the green “AVAIL” appears on the APU
GEN S/I the APU generator can be used
(Figure 6-9). Depressing the APU GEN S/I
sends a discrete signal to the GCU which con-
nects the generator to the aircraft electrical dis-
t r i bu t i o n s y s t e m . O n c e t h e g e n e r a t o r i s
connected, the APU GEN S/I “AVAIL” (green)
indication will extinguish and a white “ON”
indication will illuminate.
When the APU generator is powering the air-
craft the system responds as if the right engine
generator was on-line. The bus-tie and the
right isolation contactor will both close. The
APU generator will power all aircraft system
busses and will keep the emergency battery and
aircraft main batteries charged.
6-9
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
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