The EMER BATT is normally selected on be-
fore engine start and remains on throughout
t h e f l i g h t . W h e n t h e E M E R BAT T S / I
(switch/indicator) on the electrical control
panel (Figure 2-2) is depressed, current from
the emergency battery closes the emergency
battery contactor and the OFF indication on
the switch extinguishes. When the emergency
battery is selected OFF, the contactor will
open and the OFF indication on the switch
will illuminate, assuming at least one essen-
tial bus is still powered by another power
source.
GROUND POWER UNIT (GPU)
Ground power can be connected to the air-
plane through a receptacle located on the lower
left side of the fuselage just aft of the tailcone
baggage door (Figure 2-5). The anti-flash con-
tactor that connects the output of the GPU to
the aircraft electrical system will only close
if the voltage and polarity are within accept-
able limits. The acceptable voltage limits are
approximately 24 to 32 volts. The operator
must insure the GPU is regulated to 28 VDC
and limited to 1,500 amps.
The EXT PWR S/I (switch/indicator) is lo-
cated on the cockpit electrical control panel
(Figure 2-2). The green AVAIL caption on the
E X T P W R s w i t c h w i l l i l l u m i n a t e i f t h e
plugged-in GPU is within acceptable param-
eters. Depressing the EXT PWR switch when
the green AVAIL light is illuminated will close
the GPU anti-flash contactor, connecting the
GPU output to the left generator bus (Figure
2-19). The ON caption will illuminate and the
green AVAIL caption will extinguish. The
GPU may be deselected with the same switch.
The bus-tie contactor automatically closes
when a GPU is connected to the airplane elec-
trical system. The entire DC system is pow-
ered, assuming the avionics master and main
battery switches are on and no busses have
been deselected via the electrical control panel
(Figure 2-19).
Neither the airplane generators nor the APU
will come on-line with the GPU selected ON;
and if they are on when the GPU is selected,
they will drop off-line. Airplane generators
will automatically come on line after engine
start, but not if the GPU is selected ON. The
aircraft main batteries do not have to be on to
close the GPU anti-flash contactor; however,
only the bus-tie and non-essential bus con-
tactors will close if neither battery is selected
to ON. In this case GPU power would only be
available to the left and right generator busses,
the left and right non-essential busses, and
the hot busses.
G P U o u t p u t vo l t a g e i s i n d i c a t e d o n t h e
EICAS/MFD SUMRY page and on the ELEC
system schematic under “L/R ESS VOLTS,”
(Figure 2-10). The EMER BUS VOLTS will
also show GPU voltage. No indication of amps
drawn from the GPU is provided.
T h e C A S w i l l p r o v i d e a n “ E X T E R NA L
POWER” message (Table 2-2) when an ex-
ternal power cable is connected and “EXT
P W R ” w i l l a l s o b e a n n u n c i a t e d o n t h e
EICAS/MFD ELEC system schematic (Figure
2-10). These indications will appear when-
ever a GPU cable is connected to the airplane,
and a voltage of greater than 5 volts is sensed
by the power monitor. It is not an indication
that the GPU meets acceptable parameters nor
does it indicate that the GPU is powering the
airplane electrical system.
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
2-5
FOR TRAINING PURPOSES ONLY
FlightSafety
international
Figure 2-5. GPU Receptacle