Textron Cessna 172R - Ammeter; I Avionics Master Switch

SECTION
7
AIRPLANE
&
SYSTEMS DESCRIPTION
CESSNA
MODEL
172R
AVIONICS MASTER
SWITCH
Electrical
power
for
each
Avionics
Bus
is
supplied
from
a
primary
Electrical
Bus.
For
airplane
serial
numbers
17280001
through
17280983,
except
for
certain
non-U.S.
certified
airplanes,
both
Avionics
Buses
are
controlled
by
a
single-section
rocker-type
Avionics
Master switch.
At serial
number
17280984
and
on,
a
two-
section
or
"split"
rocker-type
Avionics
Master switch controls
power
to
each Avionics Bus
independently. Placing
the
rocker
in
the
up
(ON)
position provides
power
to
the Avionics Bus.
Placing
the
rocker
in
the
down
(OFF)
position
removes
power
from
the Avionics
Bus. The Avionics
Master switch is
located
on
the lower
left
side
of
the instrument
panel.
For
airplane
serial numbers
17280001
through
17280983,
aircraft certified
outside
the
United
States
can
have
a
two-
section
or
"split"
Avionics Master
switch.
The
two-section
Avionics Master switch enables
independent
operation
of
Avionics Bus
1
and Avionics Bus
2.
With
the
Avionics
Master
rocker
in
the
OFF
position,
no
electrical
power
is
provided
to
the
avionics,
even
when
the
Master switch
or
the
individual avionics
component
equipment
switches
are
in
their
ON
positions.
The Avionics
Master switch
(both
sides,
if
two-section)
should
be
placed
in
the
OFF
position
before
switching
the
Master
switch
ON
or
OFF,
starting
the
engine,
or
applying
an
external
'
power
source.
Each avionics
bus also
incorporates
a
separate
circuit breaker
installed between the
primary
bus
and
the
avionics
master
switch.
In
the
event
of
an
electrical
malfunction,
this breaker
will
trip
and take
the
effected
avionics bus
off-line.
AMMETER
|
The
ammeter/vacuum
gage
is located
on
the lower
left
side
of
the
instrument
panel.
It indicates the
amount
of
current,
in
amperes,
from
the
alternator
to
the
battery
or
from
the
battery
to
the
airplane
electrical
system.
When the
engine
is
operating
and the
master
switch is turned
on,
the
ammeter
indicates
the
charging
rate
applied
to
the
battery.
In
the
event
the
alternator
is
not
functioning
or
the
electrical load
exceeds
the
output
of
the
alternator,
the
ammeter
indicates the
battery
discharge
rate.
NOTE
7-34
Revision
8
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