Textron Aviation Cessna 172S NAV III Skyhawk SP, Information Manual

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SECTION 7 CESSNA
AIRPLANE AND SYSTEM DESCRIPTION MODEL 172S NAV III
KAP 140 AUTOPILOT
U.S.
ELECTRICAL SYSTEM
(Continued)
STANDBY BATTERY SWITCH
The STBY BATT master switch is a three position (ARM-OFF-TEST)
switch that tests and controls the standby battery system. The energy
level of the battery shall be checked before starting the engine, refer to
Section 4, by placing the switch in the momentary TEST position and
observing the correct illumination of the TEST lamp found to the right of
the switch. Energy level tests after starting engine are not
recommended.
Placing the switch in the ARM position during the engine start cycle
allows the standby battery to help regulate and filter essential bus
voltage during the start cycle. The switch is set to the ARM position
during normal flight operation to allow the standby battery to charge
and to be ready to power the essential bus in the event of alternator
and main battery failure. Placing the switch in the OFF position
disconnects the standby battery from the essential bus. Operation with
the STBY BATT switch in the OFF position prevents the standby battery
from charging and from automatically providing power should an
electrical system failure occur.
AVIONICS SWITCH
The AVIONICS switch is a two-pole rocker-type switch that controls
electrical power to AVIONICS BUS 1 and BUS 2. Placing either side of
the rocker switch in the ON position supplies power to the
corresponding avionics bus. Both sides of the AVIONICS switch should
be placed in the OFF position before turning the MASTER switch ON or
OFF, starting the engine, or applying an external power source.
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172SPHAUS-05
7-52
For
Training
Purposes
Only