Cessna 172 - True Airspeed Indicator; Carburetor Air Temperature Gage

I TRUE AIRSPEED INDICATOR
A true airspeed indicator is available to replace the standard air-
speed indicator in your airplane. The true airspeed indicator has a cali-
brated rotatable ring which works in conjunction with the airspeed indi-
cator dial in a
manner similar to the operation of a flight computer.
TO OBTAIN TRUE AIBSPEED, rotate ring until pressure altitude
is aligned with outside
air temperature in degrees Fahrenheit. Then '
read true
airspeed on rotatable ring opposite airspeed needle.
NOTE
Pressure altitude should not be confused with indicated
altitude. To obtain-
pressure altitude, set barometric
scale on altimeter to "29. 92" and read pressure altitude
on altimeter. Be sure to return altimeter barometric
scale to original barometric setting after pressure alti-
tude has been obtained.
CARBURETOR AIR TEMPERATURE GAGE
A carburetor air temperature gage may be installed in the aircraft to
help detecf carburetor icing conditions. The gage is marked with a yeJ:.:
low arc between -15 ° and +5 °C. The yellow arc indicates the carburetor
temperature range where carburetor icing can occur; a placard on the
gage reads KEEP NEEDLE OUT OF YELLOW ARC DURING POSSIBLE
ICING CONDITIONS.
Visible
moisture or high humidity can cause carburetor ice formation
especially in idle or low power conditions. Under cruising conditions, th;
formation of ice is usually slow, providing time to detect the loss of RPM
caused by the ice. Carburetor icing during take-off is rare since the full-
open throttle condition is less susceptible to ice obstruction.
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