SECTION 7
CESSNA
AIRPLANE & SYSTEMS DESCRIPTIONS
MODEL 172RG
Post lights (if installed) are mounted at the edge of each instrument and
provide direct lighting. To use post lighting, move the slide switch in the
overhead console, labeled PANEL LIGHTS, to the POST position and
rotate the outer knob on the light dimming rheostat, labeled PANEL LT,
clockwise to obtain the desired light intensity. When the PANEL LIGHTS
switch is placed in the BOTH position, the flood lights and post lights will
operate simultaneously.
The engine instrument cluster, radio equipment, digital clock and
magnetic compass have integral lighting and operate independently of
post or flood lighting. The intensity of instrument cluster, radio, and
digital clock lighting is controlled by the inner knob on the light dimming
rheostat labeled RADIO LT; compass lighting is controlled by the outer
knob labeled PANEL LT. Rotate the knobs clockwise to obtain the desired
light intensity. However, for daylight operation, the engine instrument,
digital clock and compass lights may be turned off while still maintaining
maximum light intensity for the digital readouts in the radio equipment.
This is accomplished by rotating the knobs full counterclockwise. The
flood lights/post lights are also turned off for daylight operation by
rotating the PANEL LT knob full counterclockwise.
A cabin dome light, in the aft part of the overhead console, is operated
by a switch near the light. To turn the light on, move the switch to the right.
A control wheel map light is available and is mounted on the bottom of
the pilot's control wheel. The light illuminates the lower portion of the
cabin just forward of the pilot and is helpful when checking maps and other
flight data during night operations. To operate the light, first turn on the
NAV LT switch; then adjust the map light's intensity with the knurled disk
type rheostat control located at the bottom of the control wheel.
A doorpost map light is located on the left forward doorpost. It contains
both red and white bulbs and may be positioned to illuminate any area
desired by the pilot. The light is controlled by a switch, below the light,
which is labeled RED, OFF, and WHITE. Placing the switch in the top
position will provide a red light. In the bottom position, standard white
lighting is provided. In the center position, the map light is turned off. Red
light intensity is controlled by the outer knob on the light dimming
rheostat labeled PANEL LT.
The most probable cause of a light failure is a burned out bulb;
however, in the event any of the lighting systems fail to illuminate when
turned on, check the appropriate circuit breaker. If the circuit breaker has
opened (white button popped out), and there is no obvious indication of a
short circuit (smoke or odor), turn off the light switch of the affected lights,
reset the breaker, and turn the switch on again. If the breaker opens again,
do not reset it.
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1 July 1979
CESSNA
SECTION 7
MODEL 172RG
AIRPLANE & SYSTEMS DESCRIPTIONS
CABIN HEATING, VENTILATING AND
DEFROSTING SYSTEM
Heated air from a muffler shroud and heater valve and ventilating air
from an external ventilating air door are supplied to a manifold just
forward of the pilot's and copilot's feet (see figure 7-9). The temperature
and volume of airflow to the manifold and then to the cabin is regulated by
manipulation of the push-pull CABIN HEAT and CABIN AIR controls.
Both controls permit intermediate settings.
Cabin heat and ventilating air from the manifold to the cabin is
supplied by two ducts, one extending down each side of the cabin to an
outlet at the front door post at floor level. Windshield defrost air is also
supplied by dual ducts leading from the cabin manifold to outlets on top of
the glare shield. Two knobs on each outlet control sliding valves which
permit regulation of defroster airflow.
For cabin ventilation, pull the CABIN AIR knob out, with the CABIN
HEAT knob pushed full in. To raise the air temperature, pull the CABIN
HEAT knob out until the desired temperature is attained. Additional heat
is available by pulling the knob out farther; maximum heat is available
with the CABIN HEAT knob pulled out and the CABIN AIR knob pushed
full in.
NOTE
For improved partial heating on mild days, pull out the
CABIN AIR knob slightly when the CABIN HEAT knob is
out. This action increases the airflow through the system,
increasing efficiency, and blends cool outside air with the
exhaust manifold heated air, thus eliminating the possibil-
ity of overheating the system ducting.
Separate adjustable ventilators supply additional ventilation air to
the cabin. One near each upper corner of the windshield supplies air for the
pilot and copilot, and two ventilators are available for the rear cabin area
to supply air to the rear seat passengers. Each rear ventilator outlet can be
adjusted in any desired direction by rotating the entire outlet. Rear seat
ventilation airflow may be closed off completely, or partially closed,
according to the amount of airflow desired, by rotating an adjustment knob
protruding from the center of the outlet.
PITOT-STATIC SYSTEM AND INSTRUMENTS
The pitot-static system supplies ram air pressure to the airspeed
1 July 1979
7-35
