SECTION 7
CESSNA
AIRPLANE & SYSTEMS DESCRIPTIONS
MODEL 172RG
high-low voltage control unit mounted on the engine side of the firewall
and a red warning light labeled LOW VOLTAGE, on the left side of the
instrument panel adjacent to the manifold pressure gage.
In the event an over-voltage condition occurs, the alternator control
unit automatically removes alternator field current which shuts down the
alternator. The battery will then supply system current as shown by a
discharge rate on the ammeter. Under these conditions, depending on
electrical system load, the low-voltage warning light will illuminate when
system voltage drops below normal. The alternator control unit may be
reset by turning the master switch off and back on again. If the warning
light does not illuminate, normal alternator charging has resumed;
however, if the light does illuminate again, a malfunction has occurred,
and the flight should be terminated as soon as practicable.
NOTE
Illumination of the low-voltage light and ammeter
dischargeindications may occur during low RPM conditions
with an electrical load on the system, such as during a low
RPM taxi. Under these conditions, the light will go out at
higher RPM. The master switch need not be recycled since
an over-voltage condition has not occurred to de-activate
the alternator system.
The warning light may be tested by turning on the landing lights and
momentarily turning off the ALT portion of the master switch while
leaving the BAT portion turned on.
CIRCUIT BREAKERS AND FUSES
Most of the electrical circuits in the airplane are protected by "
push-to-reset" type circuit breakers mounted on the lower left side of the switch
and control panel. However, a "pull-off" type circuit breaker protects
alternator output and the landing gear system hydraulic pump motor
circuit. In addition to the individual circuit breakers, a single-rocker
switch/ circuit breaker, labeled AVN PWR on the avionics panel, located
on the left cabin sidewall between the forward doorpost and the switch and
control panel, also protects the avionics systems. The cigar lighter is
protected by a manually-reset type circuit breaker on the back of the
lighter, and a fuse behind the instrument panel. The control wheel map
light (if installed) is protected by the NAV LIGHTS circuit breaker and a
fuse behind the instrument panel. Electrical circuits which are not
protected by circuit breakers are the battery contactor closing (external
power) circuit, clock circuit, and flight hour recorder circuit. These
circuits are protected by fuses mounted adjacent to the battery.
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1 July 1979
CESSNA
SECTION 7
MODEL 172RG
AIRPLANE & SYSTEMS DESCRIPTIONS
GROUND SERVICE PLUG RECEPTACLE
A ground service plug receptacle may be installed to permit the use of
an external power source for cold weather starting and during lengthy
maintenance work on the electrical and electronic equipment. Details of
the ground service plug receptacle are presented in Section 9, Supple-
ments.
LIGHTING SYSTEMS
EXTERIOR LIGHTING
Conventional navigation lights are located on the wing tips and top of
the rudder. Dual landing/taxi lights are located in the cowl nose cap.
Additional lighting is available and includes a flashing beacon mounted
on top of the vertical fin, a strobe light on each wing tip, and a courtesy
light recessed into the lower surface of each wing slightly outboard of the
cabin doors. Details of the strobe light system are presented in Section 9,
Supplements. The courtesy lights are operated by the DOME LIGHTS
switch located on the overhead console; push the switch to the right to turn
the lights on. The remaining exterior lights are operated by rocker
switches located on the left switch and control panel; push the rocker up to
the ON position.
The flashing beacon should not be used when flying through clouds or
overcast; the flashing light reflected from water droplets or particles in the
atmosphere, particularly at night, can produce vertigo and loss or orienta-
tion.
INTERIOR LIGHTING
Instrument panel and switch and control panel lighting is provided by
flood lighting, integral lighting, and post lighting (if installed). Lighting
intensity is controlled by a dual dimming rheostat equipped with an outer
knob labeled PANEL LT, and an inner knob labeled RADIO LT, located
below the throttle. A slide-type switch (if installed) on the overhead
console, labeled PANEL LIGHTS, is used to select flood lighting in the
FLOOD position, post lighting in the POST position, or a combination of
post and flood lighting in the BOTH position.
Instrument panel and switch and control panel flood lighting consists
of a single red flood light in the forward edge of the overhead console. To
use flood lighting, move the slide switch in the overhead console, labeled
PANEL LIGHTS, to the FLOOD position and rotate the outer knob on the
light dimming rheostat, labeled PANEL LT, clockwise to the desired light
intensity.
1 July 1979
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