Page 25 - Volume 15 Number 3

Ever since weather data has been able to be downloaded from the satellite to the aircraft, this topic has been discussed. Let me start by saying that this is not a scientific, laboratory type of comparison, but rather a professional pilot evaluation from real-world experience.Radar was developed in secrecy during World War II. It uses radio waves or microwaves to determine range, altitude, direction, or speed of both moving and fixed objects.Nexrad (Next-generation Radar) is a network of 159 high- resolution Doppler weather radars operated by the National Weather Service. Doppler radars can detect precipitation and wind. The National Weather Service started replacing their older radars in 1992 and the network was completed in 1997. This is the same system you already use when doing your preflight planning, watching the local news and that ATC uses when vectoring you around weather.by Chuck BlackabyI have been using airborne weather radar in many different types of aircraft as well as many different models of radar since the mid-1980s. During this time, I’ve learned that properly interpreting the radar return can be more of an art than a science. You need to be adjusting the tilt depending on the current phase of the flight. The return changes drastically in turns and extreme precipitation can even cause a return indicating no precip at all. This phenomenon is called attenuation, whereby all of the radar’s power is absorbed by the intense precipitation and none of it is returned to the antenna. These “sucker holes” can easily lure an inexperienced radar operator into the worst weather in front of you.Onboard radar systems have some very definite advantages. The first is real-time information, while Nexrad data can be several minutes old. Another plus is you can get a real feel if the weather is higher or lower than your current altitude. The radar, however, is only as good asthe operator, so a critical element in being able to make the most of your radar system is having the proper training. Some of the most popular are DVD courses put out by Archie Trammell and FlightSafety.Nexrad can be much easier to read. It clearly shows definite boundaries of precipitation in the customary three-color graduations of intensity. The display is presented as a ”God’s eye view” of the weather. It is exactly like you are sitting at your office computer while doing your preflight planning. It has also been my experience that Nexrad is more sensitive than its onboard cousin. I know many of us have been flying with the radar operating and been told by ATC that an area of light precip is ahead, but the radar isn’t painting anything. And sure enough, you fly into some light rain. Most likely, the Nexrad will show this area in green.My first use of the onboard Nexrad system was in a Cessna 421C equipped with a three-color radarMARCH 2011­TWIN & TURBINE • ­23r.NexradDan Weatherford Photo