J. MAC MCCLELLAN
COMMENTARY / LEFT SEAT
What Are Icing
Can we ever really know when ice will form?
A COMMON DEFINITION OF icing conditions is the presence of
visible moisture with an air temperature below freezing. Makes
sense. Water and cold equal ice. Works every time in the ice
maker in my freezer.
Light snow was falling at the Oshkosh
airport, but surface temperature was plus 2
degrees Celsius so the snow was melting as
it landed on the car, and on the wings of my
airplane. But it was clearly below freezing
aloft because the precipitation was falling
as snow. Were these icing conditions? The
moisture was sure visible, and it was certain that the air was below freezing at some
altitude, probably a pretty low altitude.
The radar picture showed the snow
ending about 30 miles east of Oshkosh,
just short of the western shore of Lake
Michigan. There was the usual AIRMET
for light to moderate icing over the area,
but no pilot reports of actual icing. The
ceiling varied between 600 and 900 feet,
and visibility at Oshkosh sank down to less
than a mile in the heavier snow showers,
but bounced up to 2 miles when the snowfall eased up.
Flying back home to the Muskegon airport in Michigan that day would have been
an easy call for a non-instrument rated pilot
because there was no way to do that. My
Baron has ice protection that would give
me an escape path if there was ice, and
none was reported, so deciding to depart
was not a big deal. But for those thousands
of hours I flew airplanes without ice protection, this was the kind of day that caused
the most angst.
At some altitude I would fly from above
freezing air into below freezing air, and
there was lots of moisture in the air.
Wouldn’t ice be a certainty? One would
think so, but no, ice is never a certainty.
And that’s what drives pilots and forecasters crazy about icing. The conditions to
make icing possible are very common, but
icing is actually uncommon, and icing