Icing Page: 10 of 22
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ANSWER: b. freezing rain above and ahead of you.
The aviator is responsible for reporting the intensity of icing encountered in flight, either
upon completion of the flight or as a pilot report (PIREP) during the flight. The standard criteria
for judging the intensity of structural icing is divided into 4 categories as follows:
a. Trace of Icing. Ice accumulates on a small probe (Projection from the airframe) at a rate
of one-half inch per 80 air miles flown. Icing on the air frame is perceptible, but the rate
of growth (accumulation) is nearly balanced by the rate of sublimation. The use of
deicing equipment is unnecessary except when icing continues for an extended period of
b. Light Icing. Ice accumulates on a small probe at a rate of one-half inch per 40 air miles.
Prolonged flight in light icing is hazardous and diversionary action may be necessary.
Occasional use of deicing equipment may be required.
c. Moderate Icing. Ice accumulates on a small probe at a rate of one-half inch per 20 air
miles. This excessive rate of accumulation on the airframe makes even short encounters
hazardous. Immediate diversionary action is necessary or the use of deicing equipment is
d. Heavy Icing. Ice accumulates at a rate of one half inch per 10 air miles, or less. Deicing
equpiment fails to effectively reduce or control this hazardous accumulation.
Diversionary action is mandatory.
If you accumulate 1/2 inch of ice in 45 miles of flight, you would report
a. trace icing.
S light icing.
c. moderate icing.
d. heavy icing.
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Snyder, Henry W. Icing, pamphlet, February 1971; Texas. (texashistory.unt.edu/ark:/67531/metapth46570/m1/10/: accessed April 25, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting Boyce Ditto Public Library.