Icing Page: 15 of 22
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ANSWER: d. Both a and c.
FLIGHT PLANNING AND PROCEDURES
An aviator must plan his flight to avoid areas where icing conditions exist. If the terrain will
not allow this, he should plan to fly at an altitude where the temperature is below -20 degrees C,
above the clouds, or where less hazardous ice forms. 0 degrees C to -10 degrees C presents the
most hazardous icing conditions, and if he has no other choice, the aviator may plan to fly at an
altitude where the temperature ranges between -10 degrees C and -20 degrees C as rime ice forms
more slowly than clear ice and is less hazardous.
In addition, the aviator must be alert for FREEZING RAIN, which causes clear ice to form
more quickly and thicker than any other condition. Freezing rain occurs when a warm air mass
overrides a retreating cold air mass which is at or below freezing temperature as in the diagram
FREEZ NG RAIEN-- __-- - .i_
\A '\ _
f freezing )
The key to avoid structural icing then, is knowing the altitude at which the temperature is 0
degrees C. This altitude is called the FREEZING LEVEL.
You should remember that the action you take when you encounter freezing rain must be
based on all the conditions that exist at that time. The choices of climbing, descending, or
descending and landing are all correct if the proper conditions exist.
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Reference the current page of this Pamphlet.
Snyder, Henry W. Icing, pamphlet, February 1971; Texas. (texashistory.unt.edu/ark:/67531/metapth46570/m1/15/: accessed April 30, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting Boyce Ditto Public Library.