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.
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 precipitation 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 provide 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.
