Flight Training - December 2013 - 54

CAREER PILOT»

TECH TALK

X-RAY VISION FOR PILOTS

Weather radar helps in decision making
» By Jared Dirkmaat

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MODERN AIRCRAFT DESIGNED for flight
into instrument conditions often are
equipped with weather radar. Weather
radar provides an overview to pilots
by showing areas of precipitation that
reflect a signal back to the receiver; the
heavier the precipitation (or higher its
density), the higher the rate of return.
These returns are color-coded by
intensity for easy discerning of light,
moderate, or heavy precipitation.

PRECIPITATION OR CLOUDS THAT EXIST ABOVE 20,000
FEET OFTEN ARE CONVECTIVE IN NATURE. FOR THAT REASON
(AS WELL AS PASSENGER COMFORT), BUILDUPS AT HIGHER
ALTITUDES ARE ALMOST ALWAYS AVOIDED, EITHER VISUALLY
OR WITH THE ASSISTANCE OF WEATHER RADAR.
Not only is it valuable for the crew to
be able to discern where the precipitation is, they can also use the weather
radar to determine the type of precipitation that exists.
For example, if a sharp precipitation
gradient appears, it's likely that convective activity is associated with the
precipitation. Because of the updrafts
that are generally associated with convection, precipitation tends to be more
isolated with rapid change from heavy
to light.
Conversely, a weak precipitation
gradient indicates more stratiform-type
clouds. With more stability and less lifting action, stratiform-type precipitation
will be more widespread, and at more
consistent levels, with a gradual change
from heavy to light.
One of the most important skills
related to using weather radar is managing the tilt of the antenna. Most radar
systems incorporate antenna tilt that
can be moved up or down to display
different regions of the viewable area.
This allows the crew to view precipi-

A DIVISION OF THE
AOPA FOUNDATION
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tation above the flight path during a
climb, a general cross-section during
cruise, or below the flight path during a descent. It's important to always
be aware of the antenna tilt setting to
ensure that the crew is looking at the
most relevant data.
Additionally, most radar incorporates
variable gain control. Adjusting the gain
will modify the sensitivity of the display.
Generally, using automatic gain will pro-

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vide the best results; however, manually
lowering the gain can help by eliminating very light returns to provide a clearer
picture of the stronger returns. In contrast, using a higher gain setting can be
used to try to detect lighter returns that
would otherwise be invisible.
Because these indications are
predicated on moisture content and
reflectivity, higher-altitude indications
are generally deemed less reliable. For
example, at altitudes above 20,000 feet,
even weak precipitation indications are
usually avoided. Because of the drastically colder temperatures aloft, these
returns could possibly contain hail or ice
pellets that exhibit low reflective properties and are difficult to display.
Weather radar is a tool available to
flight crews to assist in safe and comfortable flight. Just as TCAS doesn't replace
a pilot's responsibility to see and avoid
traffic, weather radar doesn't replace
the big picture out the window. It does
give pilots simulated X-ray vision to see
through clouds and assist in avoiding
heavy precipitation and turbulence.
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Flight Training - December 2013

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