Ci1eechcraft
Twin Engine (Piston)
Section X
Safety Information
instrument weather from clouds and fog. Your scope may be
clear between intense echoes; this clear area does not nec-
essarily mean you can fly between the storms and maintain
visual sighting of them.
Thunderstorms build and dissipate rapidly. Therefore, do not
attempt to plan a course between echoes using ground
based radar. The best use of ground radar information is to
isolate general areas and coverage of echoes. You must
avoid individual storms from in-flight observations either
by
visual sighting or by airborne radar. It is better to avoid the
whole thunderstorm area than to detour around individual
storms unless they are scattered.
Remember that while hail always gives a radar echo, it may
fall several miles from the nearest visible cloud and hazard-
ous turbulence may extend to as much as 20 miles from the
echo edge. The intensity of the radar echo from hail varies
with the size and nature of the hailstone. A hailstone with a
wet surface gives a strong radar return while a dry hailstone
gives a relatively weak return. Avoid intense or extreme
level echoes by at least 20 miles; that is, such echoes
should be separated by at least 40 miles before you fly
between them. With weaker echoes you can reduce the dis-
tance by which you avoid them.
Above all, remember this: never regard any thunderstorm
lightly. Even when radar observers report the echoes are of
light intensity, avoiding thunderstorms is the best policy. The
following are some do's and don'ts of thunderstorm avoid-
ance:
1. Don't land or take off in the face of an approaching
thunderstorm. A sudden gust front of low level turbu-
lence could cause loss of control.
2. Don't attempt to fly under a thunderstorm even if you
can see through to the other side. Turbulence and wind
shear under the storm could be disastrous.
May, 1994
10-37
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