Aero-Tips!
A good pilot is always learning -- how many times have you heard
this old standard throughout your flying career? There is no truer
statement in all of flying (well, with the possible exception of
"there are no old, bold pilots.")
Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators. Some of them, you
may have heard before... but for each of us, there will also be
something we might never have considered before, or something that
didn't "stick" the way it should have the first time we memorized
it for the practical test.
Look for our daily Aero-Tips segments, coming each day to you
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Aero-Tips 10.04.06
It's October, and we're already seeing a lot of Pilot Reports
(PIREPs) for airframe ice in the northern US.
All ice is hazardous to airplanes. The characteristics of ice
provide a clue as to how rapidly the situation may become
uncontrollable, and how quickly the airframe may shed ice once you
leave ice-accumulating conditions. There are three types of
airframe ice:
Rime ice. Rime ice forms a milky, opaque layer.
It looks like the frosty crystals that coat the interior walls of
your home freezer. Rime ice results when a freezing-temperature
surface (like an airplane) impacts very small liquid water
droplets. Small droplets are usually suspended in stratus-type
clouds, so rime ice usually occurs in warm fronts and slow-moving
cold fronts, in stratus clouds. Because the droplets are very small
rime ice may accumulate slowly (but don't count on it); since
stratus clouds usually extend over wide areas there is a chance
rime ice accumulation can become extremely hazardous. The good news
is that, owing to the small crystalline structure of rime ice, it
will often melt or sublimate off the airframe fairly quickly once
you exit icing conditions.
Clear ice. Clear ice results from in-flight
collisions with larger, supercooled water droplets such as you'll
find in cumulus-type clouds. Clear ice is thick and hard, like the
ice form an ice cube tray. A glossy, translucent ice layer forms,
disrupting air flow and spreading aft along wings and tail to
potentially obstruct the motion of control surfaces. Although you
may enter and exit cumulus clouds quickly, remaining in icing
conditions for short periods, the large size of water droplets in
cumulus means a dangerous coating of clear ice can form extremely
rapidly. This thick, hard ice is hard to remove, and may not melt
or sublimate away just because you exit ice-accumulating
conditions.
Mixed ice. As the name implies, mixed ice is a
combination of rime and clear ice. Mixed ice usually forms in
stationary fronts or occlusions, where you encounter cumulus clouds
embedded in layers of stratus. Mixed ice may become dangerous
quickly, like clear ice, and may be as difficult to remove.
Regardless of type, all airframe ice disrupts lift development
and can create wildly unpredictable flight characteristics. It's
wise to avoid all areas of potential ice formation, and to escape
to ice-free air at the first sign of ice accumulation -- even if
flying a "known ice" airplane.
Aero-tip of the day: Recognize the potential
for ice formation, and have a preplanned escape route should ice
begin to form.