Icing

C J Campbell wrote:

Descending out of a layer of freezing rain does not likely to work because
the cold layer may go all the way to the ground and the water will not have
formed ice pellets before reaching the ground.

That was an excellent posting, but I'd just like to add that descending can
work very well if you know for certain that the temperature below you is
much warmer, say, 5-10 degC (you can confirm the surface temp by tuning in
each ATIS as you pass it, something that I always do in cold IMC). That is
typical of spring in central Canada (and, presumably, the northeastern U.S.)
-- In Ottawa we get freezing rain or ice pellets on the ground only a few
days a year, but we have supercooled large droplets aloft for much more than
that, and they're especially problematic in early spring when we're right on
the boundary between the Gulf and Arctic air masses.

However, it is not as if the rain is invisible -- you can see rain shafts
from quite a distance. Obviously, visible rain shafts in areas of below
freezing temperatures should be avoided. The real problem comes when you are
IFR and cannot see the rain before you encounter it. If you are not equipped
for dealing with icing conditions the best strategy is to not fly into any
cloud where the temperature is near or just below freezing.

Unless you have a lot of outs, of course, such as known warmer air below
(above MEA) and/or usable approaches nearby. Typically, the cloud tops are
not high in the winter, so you'll be in IMC twice on a long cross country:
climbing up through the clouds on departure, and climbing back down through
them on arrival. In the spring, things are trickier, since the cloud tops
can be well up in the oxygen altitudes. Either way, icing does cause me to
cancel some trips.


All the best,


David