Piper PA-28-161 Pilot Operating Handbook page 50

PIPER AIRCRAFT CORPORATION SECTION 3
PA-28-161, WARRIOR II EMERGENCY PROCEDURES
3.29 CARBURETOR ICING
Under certain moist atmospheric conditions at temperatures of -5°C
to 20°C. it is possible for ice to form in the induction system, even in
summer weather. This is due to the high air velocity through the carburetor
venturi and absorption of heat from this air by vaporization of the fuel.
To avoid this. carburetor preheat is provided to replace the heat lost by
vaporization. Carburetor heat should be full on when carburetor ice is
encountered. Adjust mixture for maximum smoothness.
3.41 ENGINE ROUGHNESS
Engine roughness is usually due to carburetor icing which is indicated by
a drop in RPM. and may be accompanied by a slight loss of airspeed or
altitude. If too much ice is allowed to accumulate. restoration of full power
may not be possible: therefore. prompt action is required.
Turn carbureto:· heat on (See Note). RPM will decrease slightly and
roughness will increase. Wait for a decrease in engine roughness or an
increase in RPM. indicating ice removal. If there is no change in approx-
imately one minute. return the carburetor heat to OFF.
If the engine is still rough. adjust the mixture for maximum smoothness.
The engine will run rough if the mixture is too rich or too lean. The electric
fuel pump should be switched to ON and the fuel selector switched to the
other tank to see if fuel contamination is the problem. Check the engine
gauges for abnormal readings. If any gauge readings are abnormal. proceed
accordingly. Move the magneto switch to L then to R, then back to BOTH.
If operation is satisfactory on either magneto. proceed on that magneto at
reduced power. with mixture full RICH to a landing at the first available
airport.
ISSUED: AUGUST 13, 1982
REPORT: VB-1180
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