Electrical System; Master Switch - Cessna 1980 172RG Cutlass Pilot Operating Handbook

SECTION 7
AIRPLANE & SYSTEMS DESCRIPTIONS
7-28
CESSNA
CESSNA
MODEL 172RG
MODEL 172RG
master cylinder attached to each of the pilot's rudder pedals. The brakes
are operated by applying pressure to the top of either the left (pilot's) or
right (copilot's) set of rudder pedals, which are interconnected. When the
airplane is parked, both main wheel brakes may be set by utilizing the
parking brake which is operated by a handle below the left side of the
switch and control panel. To apply the parking brake, set the brakes with
the rudder pedals, pull the handle aft, and rotate it 90° down.
For maximum brake life, keep the brake system properly maintained,
and minimize brake usage during taxi operations and landings.
Some of the symptoms of impending brake failure are: gradual
decrease in braking action after brake application, noisy or dragging
brakes, soft or spongy pedals, and excessive travel and weak braking
action. If any of these symptoms appear, the brake system is in need of
i mmediate attention. If, during taxi or landing roll, braking action
decreases, let up on the pedals and then re-apply the brakes with heavy
pressure. If the brakes become spongy or pedal travel increases, pumping
the pedals should build braking pressure. If one brake becomes weak or
fails, use the other brake sparingly while using opposite rudder, as
required, to offset the good brake.

ELECTRICAL SYSTEM

The airplane is equipped with a 28-volt, direct-current electrical
system (see figure 7-8). The system uses a battery, located aft of the rear
cabin wall, as the source of electrical energy and a belt-driven 60-amp
alternator to maintain the battery's state of charge. Power is supplied to
most general electrical and all avionics circuits through the primary bus
bar and the avionics bus bar, which are interconnected by an avionics
power switch. The primary bus bar is on anytime the master switch is
turned on, and is not affected by starter or external power usage. Both bus
bars are on anytime the master and avionics power switches are on.

MASTER SWITCH

The master switch is a split-rocker type switch labeled MASTER, and
is ON in the up position and off in the down position. The right half of the
1 July 1979
1 July 1979
AIRPLANE & SYSTEMS DESCRIPTIONS
CAUTION
Prior to turning the master switch on or off, starting the
engine, or applying an external power source, the avionics
power switch, labeled AVN PWR, should be turned off to
prevent any harmful transient voltage from damaging the
avionics equipment.
SECTION 7
7-29