ELECTRICAL SWITCH
INDICATORS (S/I’S)
Following is a description of the S/Is (switch
indicators) on the electrical control panel:
L/R BATT – The battery switches are mo-
mentary action switches. If the aircraft elec-
trical system is powered (one BATT, GPU,
APU or generator ON), the OFF caption will
be illuminated in the L/R BATT switch (Figure
2-9) whenever the corresponding battery con-
tactor is open. If the battery meets satisfactory
voltage and temperature conditions, the OFF
caption will extinguish when the switch is
momentarily depressed and the battery con-
tactor will close, connecting the battery to the
respective generator bus. The switch will be
blank when the battery is on. It will also be dark
(with no OFF annunciations illuminated) when
there is no electrical power applied to the air-
plane even though the contactor would be open
in this case. The battery contactor will open
and the OFF caption will illuminate if the bat-
tery switch is depressed a second time or if the
battery is automatically turned off due to an
overheat or an undervoltage condition.
BUS-TIE – Normal automatic operation of
this momentary action switch displays a hor-
izontal bar when the generator busses are tied
and no indication will be illuminated when the
busses are split.
If required, this switch may be depressed to
manually over-ride an automatic bus-tie op-
eration to provide a split system or to tie the
electrical system together. One exception is
that it cannot be used to open the bus-tie when
it has been closed automatically due to GPU
operation. The bus-tie manual selection may
also be used, in accordance with AFM proce-
dures, to close the bus-tie if it fails to auto-
matically close within five seconds after an
inflight generator failure. When the bus-tie
switch is depressed, a MAN (manual) caption
is illuminated to show that the automatic op-
eration is disabled and the bus-tie will be held
in the existing position until deselected by
the crew. The bus-tie cannot be manually
closed when operating on battery power only.
The CAS also provides a BUS TIE CLSD and
BUS TIE MANUAL message (Table 2-2).
EXT PWR – The external power switch is
a momentary action switch. The green
“AVAIL” caption will illuminate only when a
supply of correct voltage and polarity is sensed
on a connected GPU. When the EXT PWR
switch is pressed to provide external power to
the aircraft, “AVAIL” extinguishes and the
white “ON” is illuminated. The ON caption in-
dicates that the contactor is closed, connect-
ing the GPU to the left generator bus.
APU GEN – The APU GEN switch is a mo-
mentary action switch. The green “AVAIL”
illuminates when the APU generator is in gen-
erating mode and ready to be connected to the
aircraft electrical system. When pressed, the
AVAIL caption extinguishes and the white
“ON” is illuminated. If the switch is depressed
again, ON is extinguished and AVAIL is re-il-
luminated until the APU falls below 92% nor-
mal rpm.
L/R GEN – These are momentary action
switches. Normal generator operation is au-
tomatic and the OFF indication changes with
the on/off-line operation of the generator. If
a battery or APU engine start is made, the
generator will automatically come on-line
after start and the OFF caption will extin-
guish. If the start is made with GPU power con-
nected, the generators will not come on-line
until the GPU is deselected or disconnected.
With the generator on-line, the pilot may se-
lect to over-ride the automatic operation and
select it off-line by pressing the generator
switch. Depressing the switch when the gen-
erator is off-line also initiates a reset signal to
the GCU which eliminates the need for a sep-
arate momentary generator reset switch.
When using either the L or R GEN S/I to at-
tempt a generator reset, it may be necessary
to hold the S/I depressed up to 5 seconds if the
engine is at idle or low rpm. In flight, or at nor-
mal engine speeds, depressing the GEN S/I for
a maximum of one second is adequate for gen-
erator reset.
LEARJET 45 PILOT TRAINING MANUAL
2-10
FOR TRAINING PURPOSES ONLY
FlightSafety
international
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