BendixKing IN-182A System RDR-2000 - Manual (Page 12)

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Effective Date: 5/98 RDR 2000 Pilot's Guide: Rev 3
Theory of Operation
WEATHER RADAR PRINCIPLES
Airborne weather avoidance radar, as its name implies, is for avoiding
severe weather, not for penetrating it. Whether to fly into an area of
radar echoes depends on echo-intensity, spacing between the echoes,
aircraft capabilities and pilot experience. Remember that weather radar
detects only precipitation drops; it does not detect minute cloud droplets,
nor does it detect turbulence. Therefore, the radar provides no assur-
ance of avoiding instrument weather in clouds and fog. The indicator
may be clear between intense echoes; this clear area does not neces-
sarily mean it is safe to fly between the storms and maintain visual
sighting of them.
The geometry of the weather radar radiated beam precludes its use for
reliable proximity warning or anti-collision protection. The beam is char-
acterized as a cone shaped pencil beam. It is much like that of a flash-
light or spotlight beam. It would be an event of chance, not of certainty,
that such a beam would come upon another aircraft in flight.
Note: Weather avoidance radar is not practical as a pilot operable ter-
rain or collision avoidance system. Weather analysis and avoidance are
the primary functions of the radar system.
RADAR BEAM ILLUMINATION
Probably the most important aspect of a weather radar is the antenna
beam illumination characteristic. To make a proper interpretation of what
you are seeing on the display, you must have an understanding of what
the radar beam “is seeing”. The following figure is a side view of the
radar beam characteristic with a storm depicted at a distance that causes
the size of the storm to just fill the 3 dB beamwidth. This would be the
typical situation for a storm at approximately 40 nautical miles with a 12
inch diameter antenna. It’s important to understand and visualize this sit-
uation, to enhance your understanding of the rest of this manual. First
some observations are in order: