PDF Version October November 2008 - Midwest Flyer

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Factors To Consider When Making Weather Decisions
by Jeffery Taylor
Aviation Education Consultant
WisDOT Bureau of Aeronautics
In my role as an Aviation Education
Consultant for the Wisconsin
Department of Transportation, I
frequently have the opportunity to meet
with groups of pilots throughout the state
to discuss aviation safety and related
issues. At one of these forums, a pilot asked a difficult,
but very good question: Are there any firm or established
guidelines to help a pilot determine when weather
conditions are bad enough to cancel a planned flight?
We often ask ourselves: Should I fly into the weather
conditions that flight service is reporting or forecasting
as marginal? Should I take off, even though I’m not
comfortable with the way the weather looks? These are
questions that all pilots have asked themselves at some point
in their flying career. They’re very important questions, too,
because the safe outcome of a flight may depend entirely
on how they're answered. Unfortunately, the answers can
never be cut and dried. Sure, it’s possible to come up with
some general rules of thumb concerning hazardous weather
and what to avoid, but that's not enough. Accident reports
continue to describe situations where pilots knowingly took
off into thunderstorm conditions or equally bad weather. So,
rules of thumb, such as “don’t fly through an area defined
in a convective sigmet,” while good advice indeed, doesn’t
always seem to translate into real-world application. The
go/no-go decision is, of course, a matter of pilot judgment.
While weather conditions are important ingredients in the
decision, they’re not the only considerations. The other
variables are the pilot, the aircraft and its equipment, and the
geography along the proposed flight path.
First, let’s consider the weather. We all know it’s
changeable. We know that forecasts can be incorrect, and
we know to be prepared for unanticipated adverse weather
by constantly having an alternate airport in mind. But each
weather situation is different. The go/no-go decision may
42 OCTOBER/NOVEMBER 2008 MIDWEST FLYER MAGAZINE
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be clear-cut, in which case the decision is easily made, but
it may also be quite indefinite, in which case the decision
can be stressful.
Let’s take a clear-cut situation for our first scenario: A
convective sigmet for a widespread area of moderate icing
is forecast along your flight route. Your route takes you
near a center of low pressure, so there’s plenty of lifting,
which means tops are apt to be high. There’s plenty of
moisture in the air, as shown by close temperature/dew
point spreads at stations along the route, so cloud bases are
low. There are mountains along the route, which always
make for the worst icing conditions. All of this bad news is
backed up by a slew of PIREPs confirming the accuracy of
the reports and forecasts.
Here, the decision is easy: Don't go. But, what about
situations where things aren’t so definite? Let's say an icing