Wednesday, May 09, 2007

Weather Radar at ARTCCs

This is a technical article aimed primarily at air traffic controllers in the En Route option. It is my opinion only, based on my experience as a controller at Atlanta ARTCC from 1981-2006. While I will quote several FAA policies and/or orders, don’t confuse my opinion with same. The only interpretation of the rules that counts -- right or wrong -- is the FAA’s.

I believe it would be helpful if you would take the time to read an article I wrote that was published on AVweb.

Say Again? #71: Weather Radar

If you’re not already a subscriber to AVweb, you’ll have to join to access the article. It’s free and relatively painless. I also believe it is worthwhile.

It was written for an audience comprised mainly of General Aviation pilots. Controllers should pay particular attention to the final paragraphs. This is the area that I wish to expand upon. I’m not limited by space constraints here on my blog (nor the need to appeal to a commercial audience) so be forewarned, this might get lengthy.

The Quandary

Rightly or wrongly, the flying public expects air traffic controllers to help protect them from dangerous weather. Many pilots believe that includes vectors around thunderstorms. This is what the 7110.65 says about the subject.


Weather Information


a. Issue pertinent information on observed/reported weather and chaff areas. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas.

1. Issue weather and chaff information by defining the area of coverage in terms of azimuth (by referring to the 12-hour clock) and distance from the aircraft or by indicating the general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.



Pilots, and others unfamiliar with the 7110.65 read that and say “See, you are supposed to tell us about the weather and vector us around it.” It’s quite understandable but it’s also not quite correct. It’d be more accurate to say it’s qualified by the rest of the 7110.65. “Weather and Chaff Services” fall under the heading of “Additional Services”.

ADDITIONAL SERVICES- Advisory information provided by ATC which includes but is not limited to the following:

e. Weather and chaff information.

f. Weather assistance.


Furthermore, you need to read this from Chapter 2 of the 7110.65 to have an understanding of a controller’s obligations.



The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic. In addition to its primary function, the ATC system has the capability to provide (with certain limitations) additional services. The ability to provide additional services is limited by many factors, such as the volume of traffic, frequency congestion, quality of radar, controller workload, higher priority duties, and the pure physical inability to scan and detect those situations that fall in this category.”

(emphasis added)

You could spend most of your career learning the ins and outs of reading the 7110.65 (and you should.) You could spend another career (if you had the time) on learning the dynamics of a typical thunderstorm. You would still be lacking in knowledge of an atypical one. I don’t know about you, but I could spend a lifetime trying to understand all there is to know about radar and still not get it. All the science and mechanics are simply beyond my capabilities to understand.

The point is that we can’t be experts at all things. We can, however, learn enough to be experts in our field -- Air Traffic Control. We can learn enough to be safe controllers.

Tell Them What You See

I’m going to go into a lot of detail but before I do, I want you to take this one point to heart. Despite lawyers being...well, lawyers...even if weather is unpredictable...even if you’re mechanically challenged like me and radar might as well be magic -- at a minimum -- you can tell a pilot what you see.

"Heavy to Extreme precipitation between ten o'clock and two o'clock, one five miles. Precipitation area is two five miles in diameter."

Even if you think you might be wrong. It falls under the heading of “better safe than sorry.”

Speaking of being wrong, we all know that many times our weather radar is. Wrong, that is. And this is where I want to start. It’s easier to determine if your radar is wrong than it is to determine if it is right. Today is a perfect example. It’s absolutely beautiful outside. Sunny, blue, blue, blue and there’s not a cloud in the sky. It’s a great time to push the WX-1 and WX-3 buttons and get a view of the weather returns from the ARSRs. That’s right, the “old” weather radar.

I bet if I did this at Atlanta Center I’d find a dozen scopes cluttered with “permanent” weather. Which, of course, is the reason many of you don’t trust it and I suspect a fair number of you don’t use it. This problem has led many of us down the wrong path. The weather information derived from the ARSR sites is important. And it should be accurate. If it isn’t, it’s your job to report it. It’s the FAA’s job to fix it.

This is also in Chapter 2 of the 7110.65.


h. The supervisory traffic management coordinator-in-charge/operations supervisor/controller-in-charge shall verify the digitized radar weather information by the best means available (e.g., pilot reports, local tower personnel, etc.) if the weather data displayed by digitized radar is reported as questionable or erroneous. Errors in weather radar presentation shall be reported to the technical operations technician and the air traffic supervisor shall determine if the digitized radar derived weather data is to be displayed and a NOTAM distributed.

Fix the Problem

I know many of you have an overwhelming desire to write something bad about the FAA these days. Try this subject. If you think filling out an FAA form is a waste of time (and it’d be hard to argue against it), at least tell your supervisor and then fill out a NASA ASRS form documenting that you told your supervisor about it. The NASA Aviation Safety Reporting System is the best friend controllers ever had. Use it.

Hopefully, some new guy out there is reading this and wondering why the ARSR (that’s Air Route Surveillance Radar) weather display is important. I cringe to think one of them might not even know what I’m talking about. But I know how poor the FAA’s training is on this subject so I’ll explain it a little.

What have you been told is the biggest problem with WARP (NEXRAD) ? The update (refresh) rate, right ? The ARSR weather display doesn’t have that problem. It’s updated every time your traffic is updated. Every 10 seconds or so. Put your thinking cap on because there are several things to notice and I don’t have time to explain everything. At least not in one article.

Your traffic (targets) and WARP (Weather and Radar Processor) update at different rates. That could be important one day. If you’ll use it, your ARSR weather data updates faster and it can complement and enhance what WARP is telling you. If you’re getting a hit on a target (say at 8,000) you know that your ARSR should be able to see any significant precipitation at that altitude. If you’re just using WARP for weather information -- and you work in mountainous terrain like I did -- you can’t be sure that WARP is giving you any information at that altitude. This is just one area where you need to realize how poor the FAA’s training is on this subject. I don’t know the location of the NEXRAD sites covering my airspace. How about you and your airspace ? (Sorry, it’s hard for me to talk in the past tense. Forgive me if I slip up and forget I’m not a controller anymore.)

Here’s something that many old-timers know but don’t really know. The lines on the ARSR weather display (WX-1) radiate outward from the radar site. A picture will make this a lot easier so go to this site. Scroll down to the second image and take a look. (Here’s a viewing hint. If you’ll download the picture to your hard drive and open it with a graphics program you can “zoom in” to see a lot of detail. You can even read the keys in the top left of the frame. Those “NX” keys don’t look like any NEXRAD filters I ever worked with.) Do you see how the lines radiate outward from the radar site in the middle of the screen ? Look west (left) a little. See where another set of lines cross the ones radiating from the center ? That means the precipitation is high enough that a second ARSR site is painting it. It gives you a rough idea on the altitude of the precipitation. If those “crossed” lines start getting closer and closer to the radar site in the center, you know that the precipitation is getting higher and higher (like in a thunderstorm.)

Some of you younger guys might not believe it but some of us used nothing but this display to vector airplanes around thunderstorms. There was a time when controllers could trust their weather radar displays, back before the FAA started doing to AF (Airways Facilities) what they are doing to controllers now. The radar sites used to be kept “tuned up.” In other words, if you had a problem, it’d get fixed in a reasonable time frame. It’s a long story but ask some of the (few) older AF techs about it. Their story will sound familiar. Depressing, but familiar.

Building Trust

Anyway, back to learning about weather radar. It isn’t something you can learn from a book. You have to watch. And you have to watch for years. Whenever you have some thunderstorms, pay attention. See how they move. See how they change. You’ll start to recognize patterns. Pretty soon, you’ll notice the ones that don’t follow a pattern. That is when you know you’re getting somewhere.

If you follow this train of thought, you’ll see the wisdom of having a standard setting for the weather display. I know many controllers want to use the filter keys available with WARP. I played with them for a little bit when they first came out and decided they were “lying” to me. Oh, I’m sure they were accurate -- in a computer-programming geek fashion -- but they weren’t telling me the whole story. And I was used to seeing the whole story before WARP came along.

Think of a severe thunderstorm in the building stages. On the radar display, it will start out as moderate rain (dark blue/WX-1/radiating lines) and keep building up (literally “up”) through the heavy rain (cyan-checkerboard/WX-3/”H”s) until it reaches the extreme level (light blue/also “H”s.) Now let’s say you’re working in the ultra high sectors and you decide you don’t want to look at all that “clutter.” You just select the highest altitude settings on WARP (I think ours were 350-600) and all that “clutter” disappears. So what happens ? You lose all that “clutter” (that I call information) and pilots start deviating around stuff that you can’t see. You may not see the thunderstorm building but the pilots do. Just because the precipitation hasn’t reached the height that you’ve selected doesn’t mean the clouds haven’t reach that height. Those clouds are bumpy and the pilots know it. They aren’t going to fly through them.

Be honest now, how many times have you seen this happen and the controller working it complains that the weather radar isn’t worth the electricity it costs to display it ? Whereas, if he’d been looking at all the information -- from the ground up -- he would have had 1o-20 minutes warning that that the pilots were going to start deviating. And a pretty good idea on which way they’d go. Another thing while we’re here. The wind blows. At FL350 it can blow real hard. The tops aren’t necessarily where the bottoms (and the precipitation returns) are. In other words, the deviations you observe might not correspond exactly to what you see on the radar in the higher altitudes.

What bothers me most about using the filter keys on WARP is what it does to my observation habits. To sum it up, I’d rather let my brain filter out the information than let the computer do it. I don’t want to try and figure out the differences in the patterns I observe at 000B240, 240B350 and 350B600. I’d rather have all the information -- just one pattern to learn -- in my mental picture and sort it out from there.

I think it’s worth pointing out that there are two unique mindsets at work here. I’ve spent a lot of time talking about how to use your ability to observe to help you work your traffic. It’s very helpful if you’ll take the time to learn it but it is actually secondary in terms of importance. The most important part is to keep airplanes out of the thunderstorms.

Working Low

Unfortunately (at least when it comes to thunderstorms), Center controllers spend most of their time working airliners at relatively high altitudes. These aircraft have good weather radar and usually enjoy good visibility at the higher altitudes. It is the common frame of reference for Center controllers. This changes dramatically when we find ourselves on the low sectors.

Many of the airplanes don’t have weather radar. Many times the pilot (and many times it’s a single pilot) doesn’t have good visibility. If you’ve spent most of your career on the high sectors with most of the weather radar information turned off, you won’t have a good idea about how the thunderstorms act. It is proving to be a deadly combination. And there’s one other point we need to return to here...if you’ve been told over and over again that airliners have better weather radar than you do...if you have most of the weather radar information turned simply aren’t in the habit of telling the pilot what you see. It’s a habit you need to have.

I cannot over stress this point. At a minimum (time permitting) you need to tell all pilots what you see. Make it a habit. It’s a good one.


a. Issue pertinent information on observed/reported weather and chaff areas. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas.

You’ll notice that doesn’t say except airliners. You should tell the airliners what you see. I don’t care how many times they come back with a bored, why-are-you-bothering-me tone, “Yeah, we see it.” It’s the times they don’t see it that count. It doesn’t say except when they’re in VFR conditions. And that brings up another point that we need to stop and discuss.

Center controllers don’t know when pilots are in VFR conditions. You may know that it was VFR five miles back or five minutes before, but you can’t look out the window and tell what kind of weather we’re having at this exact moment. I am dumbfounded at the number of times I’ve seen a controller assume that a C172 cruising along at 5,000 on a VFR summer day was actually in VFR conditions. On the East Coast, even on days without that many clouds, visibility is usually below 10 miles during the summer. Don’t assume a pilot on an IFR flight plan is in VFR conditions. Don’t assume a VFR pilot receiving VFR flight following can see a thunderstorm 20 miles ahead.

No Excuses

As I mentioned earlier, many controllers want to tell you that airliners have better radar than controllers do. Before NEXRAD, I would have agreed. (Note: You still had to tell them what you saw.) Now, you (the controller) have better weather radar data than they do. But, but, but.....But WHAT ? NEXRAD is what the National Weather Service uses. It’s their product. (That’s important. Pay attention. It’s a NWS product, not an FAA product.) It was specifically designed for weather. NEXRAD is the finest weather radar available. So what’s the excuse now for controllers that don’t want to trust their weather radar display ?

Here, let me give you a couple. It updates slowly. That’s true. Depending upon your NEXRAD coverage and how fast a line of thunderstorms is moving, it can be a real problem. The ARSR weather data doesn’t have that problem. Turn it on. Problem solved. Next excuse.

A lot of pilots have their own NEXRAD display now. Why should we have to tell them what we see when they’re looking at the same data ? You mean that same data that other controllers don’t want to trust ? Seriously, we can’t have it both ways. You can’t tell a pilot to bet his life on the same data that you aren’t willing to trust. Some pilots have NEXRAD, some have their own weather radar and some even have both. They still don’t have all the data that you have available to you. You have the NEXRAD mosaic and the ARSR mosaic. There’s not a pilot in the sky that has those tools. Except through you. Tell them what you see.

That is enough to chew on for now. We’ll get to the second part -- When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas. -- at a later date.

(Note: For those NATCA members that would like to discuss this article, please see the topic that will be started on For others, go back to the top of the page and click on “View my complete profile.” You’ll see a link to my e-mail address when you click on that link.)

Don Brown
May 9, 2007

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