PRIMUSR 660 Digital Weather Radar System
A28–1146–111
REV 2 A–9
Federal Aviation Administration (FAA) Advisory Circulars
DDon’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.
DDon’t fly without airborne radar into a cloud mass containing
scattered embedded thunderstorms. Scattered thunderstorms not
embedded, usually can be visually circumnavigated.
DDon’t trust the visual appearance to be a reliable indicator of the
turbulence inside a thunderstorm.
DDo avoid, by at least 20 miles, any thunderstorm identified as severe
or giving an intense radar echo. This is especially true under the
anvil of a large cumulonimbus.
DDo circumnavigate the entire area if the area has 6/1 thunderstorm
coverage.
DDo remember that vivid and frequent lightning indicates the
probability of a severe thunderstorm.
DDo regard as extremely hazardous, any thunderstorm with tops
35,000 feet or higher, whether the top is visually sighted or
determined by radar.
If you cannot avoid penetrating a thunderstorm, the following are some
do’s BEFORE entering the storm.
DTighten your safety belt, put on your shoulder harness if you have
one, and secure all loose objects.
DPlan and hold your course to take you through the storm in a
minimum time.
DTo avoid the most critical icing, establish a penetration altitude below
the freezing level or above the level of –15 _C.
DVerify that pitot heat is on and turn on carburetor heat or jet engine
anti–ice. Icing can be rapid at any altitude and cause almost
instantaneous power failure and/or loss of airspeed indication.
DEstablish power settings for turbulence penetration airspeed
recommended in your aircraft manual.
DTurn up cockpit lights to highest intensity to lessen temporary
blindness from lightning.
DIf using automatic pilot, disengage altitude hold mode and speed
hold mode. The automatic altitude and airspeed controls of the
aircraft increase maneuvers, thus increasing structural stress.