Icing Page: 16 of 22
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ANSWER: a. Carburetor ice can be detected by noting a slow decrease in manifold pressure.
Pitot Ice is one of the more dangerous forms of inflight icing. Not in the same sense as wing
or rotor blade icing, of course, but dangerous nevertheless. Consider the following:
In normal operation, the pitot tube measures the speed of ram (incoming) air, and sends this
measurement to the airspeed indicator. Devices within the airspeed indicator compare the
difference between the ram air pressure and the static air pressure, and convert this difference to
an airspeed reading.
If the pitot tube becomes clogged (by ice, in this case) the inflow of ram air will be inhibited
or stopped completely. The airspeed indicator thus becomes an unreliable instrument; and since
the airspeed indicator is one of the primary instruments needed for IFR flying, a potentially fatal
situation is created. As you can readily see, pitot icing should be prevented before you are placed
in such a situation.
An Army aircraft that is certified for instrument flying conditions (where the presence of ice
is known or forecast) is equipped with a pitot heating system. How this system works is
unimportant at this time-suffice to say that you should turn on the pitot heat anytime there is
the slightest chance of encountering icing conditions. Remember, pitot heat is most effective
when used as anti-icing rather than de-icing equipment.
Which statement(s) best apply to a pitot tube icing condition?
a. Your airspeed will change greatly.
b. Your manifold pressure will drop.
( Erroneous airspeed will be reflected on the airspeed indicator.
d. Both a and b above.
Here’s what’s next.
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Snyder, Henry W. Icing, pamphlet, February 1971; Texas. (texashistory.unt.edu/ark:/67531/metapth46570/m1/16/: accessed June 24, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting Boyce Ditto Public Library.