Page 22 - Volume 18 Number 8

WX MAPlook like thunderstorms, are actually only convective cells. They often produce heavy rain, perhaps a severe bump, most likely not. They often produce a weak red echo. So, when you see red in an echo, before panicking and deviating 20 miles, you must discover whether it’s actually a thunderstorm or only a rain shower. To make that determination, you must know how red it is. Once upon a time, radar manufacturers gave us displays that showed magenta, in addition to the three basic colors. Many of you probably fly with one. But, several years ago, a bunch of radar engineers and salespersons got together with bureaucrats and decided that magenta is not needed. All a pilot needs to know is whether it’s got basic red in it or not. If ithas, tell them to avoid it by 20 nm. Problem solved, safety insured – and lawsuits against radar manufacturers eliminated.All true. But also true that, if the rule is followed, aviation and all its benefits to society will grind to a near halt from April through September, especially in terminal areas. To resolve that, we need more realistic guidance than the 20 nautical-mile rule, which means that when we see a red echo we need to know if it’s barely red or very, very red. Several radar tricks are available to assist us in doing that.With most general aviation radars, when you see a red weather echo, just switch to MAP mode for a couple of sweeps. If the echo drops from three color levels to only two, it’s probably only a Level 3 in hazard potential. (Be no more than 25 nm from the echo, which is the “Calibrated” range of most radars being flown by Twin and Turbine readers.) On some radars, the color shift will be from green, yellow and red to only green and yellow, on others, to only cyan and yellow. It’s not exact, but if the echo drops from three levels to only two, that’s a strong clue it’s Level 3, no stronger. (Next time you see a red weather echo, try switching to MAP with your radar to establish whether or not it works for you.)20 • TWIN & TURBINEAUGUST 2014