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Into the Shadow

So you want to get your instrument rating as a pilot. You can now fly in less than VFR weather and shoot approaches down to minimums. I want to take this time to talk about onboard weather radar, the difference between NEXRAD weather and onboard radar, their uses and limitations, and how I use them in flight.


So what is the difference between the two radars? NEXRAD radar is a datalink-driven radar. Weather information is collected and sent to satellites then sent to the airplanes. It is super accurate information for the location of thunderstorms and bad weather. We use NEXRAD weather when we pull up the weather on our computers. The downside to NEXRAD is that it can take upwards of 15 minutes to load new data. This means the information that you are seeing could be 15 minutes old. The weather that you are looking at has moved on 15 minutes down the road.


Onboard weather radar is a function of the aircraft. Many jets and higher-end aircraft have radar domes inside the aircraft. Most jets have a radar dome in the nose of the aircraft. When this function is turned on the radar sends out a signal. That signal will bounce off objects like the ground, city buildings, and rain droplets. If there is no object in its way, it will not bounce back to the radar dome. The more signal that is bounced back the more dense that object is.


One of the big problems with onboard weather radar is that it can cause a black shadow. If there is enough signal reflected back to the radar and it cannot penetrate through a heavy storm, you will see a black shadow. This has lured many pilots to make poor decisions when there was a massive storm lurking in the shadows. This limitation is called attenuation.


Pilots who use onboard weather radar should be aware of the limitations of their radar. It could mean the difference between a great ride and a dangerous ride.


How do I use this in flight? Our aircraft has both NEXRAD and onboard weather radar. When precipitation is present, I like to have my NEXRAD up on the screen. This allows me to know where the storms were. I just keep in mind that those cells that I see on NEXRAD could be 15 minutes old and may have already moved. I will also have my onboard weather radar going. This allows me to get real-time information as to the reflection of water droplets out there. If I know there is a storm nearby and my onboard weather radar is painting a red picture in front of me, then I turn and stay away from that thing.


I hope this gives you a glimpse into how we use radar. If you are a pilot, be sure to get training on your weather radar systems. They are a great tool but only if you know their limitations.


Keep the Sunny Side Up and the Airspeed in the Green


Rick Thompson

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