Pitot-Static System And Instruments - Cessna 172R Pilot Operating Handbook

PITOT-STATIC SYSTEM AND INSTRUMENTS
The pitot-static system supplies rann air pressure to the airspeed
indicator and static pressure to the airspeed indicator, vertical speed
indicator and altimeter. The system is composed of a heated pitot
tube mounted on the lower surface of the left wing,
an external
static port on the lower left side of the forward fuselage, and
the
associated plumbing necessary to connect the instruments to the
sources.
The heated pitot system consists of a heating element in the pitot
tube, a 5-amp switch/breaker labeled PITOT HEAT, and associated
wiring. The switch/breaker is located on the lower left side of the
instrument panel. When the pitot heat switch is turned on, the
element in the pitot tube is heated electrically to maintain
proper
operation in possible icing conditions.
A static pressure alternate source valve is installed below the
throttle,
and can be used
if the external static
source is
malfunctioning. This valve supplies static pressure from inside the
cabin instead of the external static port.
If erroneous instrument readings are suspected due to water
or
ice
in the pressure line going to the standard external static
pressure source, the alternate static source valve should be pulled
on.
Pressures within the cabin will vary with open heater/vents and
windows. Refer to Section 5 for the effect of varying cabin
pressures
on airspeed readings.
Dec 2/96
7-41
CESSNA
SECTION 7
MODEL 172R
AIRPLANE & SYSTEMS DESCRIPTION