Say Again? #36: Spring is Sprung

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Time once again for the weather to bring nasty thunderstorms into your favorite airspace. Some planes have long had on-board radar, and recently we've started to see NEXRAD radar on those GA glass-cockpit displays. This spring, AVweb's Don Brown finally has NEXRAD available on his radar scope. But keeping us out of thunderstorms never is that easy, is it?

Say Again?

Trying to guess what Mother Nature is going to do is risky business. I had to wait three weeks to get my yard aerated because it wouldn't stop raining. I finally got it done, threw down a bunch of grass seed and I bet it hasn't rained an inch in the month since.

Mother Nature will fool you. You may be shoveling snow where you live but down here it's time to start thinking about thunderstorms -- the big, fast-moving, nasty kind of thunderstorms. The kind that bring hail, microbursts and tornadoes with them. Just like the azaleas, they are a sure sign of spring in the South.

Have I mentioned how much I hate thunderstorms? Oh yeah, I have. I occasionally go back and read some of my old stuff just to see what has changed. Thunderstorms haven't changed (of course), but our displays at the Centers have.

Color My World

We now have color weather radar. I know the weather guy on the local TV station has had it for years, but we haven't. What that means to you, the pilot, is that we're kind of new using the equipment. We received color capability when the Display System Replacement (DSR) radar scopes were installed. That was followed shortly by a program designed to display the National Weather Services' NEXRAD product on our air traffic control scopes.

Now when I say "program," I mean a computer program. It's a computer program that makes it all happen. The other significant piece of information buried in that statement is that the radar belongs to the National Weather Service. Both of those points are important, so let me explain them.

All of the radar data in a Center is run through a computer before it is displayed on the Center controller's scope. Centers use several Air Route Surveillance Radars (ARSR) to provide continuous and redundant coverage in our airspace. Most (but not all) of these radars have "primary" capability. In other words, the radar will "paint" anything that's out there (to some degree) including precipitation. That is opposed to "secondary radar," which only interrogates and "paints" transponders. So the typical ARSR has "secondary" radar in addition the "primary" radar that we used to "paint" precipitation and aircraft without transponders.

Painting a Picture

Now we have added a third layer of radar, NEXRAD, to our displays. As I said earlier, this data comes from the radars run by the National Weather Service. These radars were designed specifically to paint weather (as opposed to airplanes.) How the radar does that is significant in understanding how it is presented on our radar scope.

NEXRAD radar actually makes several scans of an area, painting (or scanning) different altitudes with each sweep of the radar. That allows it to determine the height (or altitude) of the precipitation. Whereas an ARSR radar only showed precipitation without any indication of height, NEXRAD can give you a lot of data about the height of a storm. As most of you have already figured out, that's important when thunderstorms start reaching into the Flight Levels.

The catch is that it takes NEXRAD a relatively long time (in terms of ATC) to gather and present that data. An ARSR scans the sky six times a minute. It refreshes the data presented on our radar scope every 10 seconds. NEXRAD, on the other hand -- because its makes multiple scans -- only refreshes the data every six minutes.

WARP Factor One

Are you still with me? If we (controllers) try to vector you around a thunderstorm based only on the data derived from NEXRAD, we could be using some really old data. And you could be in for a nasty surprise.

It took me a while to figure this out. The FAA refers to the program that converts the NEXRAD data for ATC use as Weather and Radar Processor (WARP). The training on WARP was pretty much like any other training the FAA does: They pretend to tell you what you need to understand about it and controllers pretend to pay attention. Then we figure out how to really use it when we get it in the real world.

They tell you that the refresh rate is slow. The first time you use it to vector an airplane on the east side of a thunderstorm you figure out why that is important. I try to keep airplanes out of the moderate rain by at least five miles (I like 10 miles better) when a pilot asks for a vector. Just as you think you've got the guy around the corner, the display updates. Depending on how fast the weather is moving, your 10 miles just went down to five or maybe even zero.

That will catch your attention the first time it happens. I bet it's left a few pilots wondering just how close to a thunderstorm Center was going to vector them, too.

Clutter My World

I've taken to running both WARP and the old weather display at the same time. This makes a lot of controllers slightly crazy because of all the clutter it generates. Especially on the low sectors. You have to remember that we're looking at beacon targets, primary targets, sector borders, airways, airports, data blocks, various and assorted fixes, final-approach courses, and in the case of some sectors, the boundaries of the minimum-instrument-altitude areas. That is a lot of info on one display. Anybody who has ever looked at a map that tried to cram too much information into a small area knows that sooner or later you reach a point of diminishing returns.

I seem to have a larger capacity to deal with visual clutter than most controllers. When WARP came out, most of them stopped using the old weather display. Of course some of them have stopped displaying airways, too. There are even some who stopped displaying primary targets. But that's another story.

As I mentioned earlier, WARP is in color. Controllers never had color displays before DSR, and WARP was one of the first things to take advantage of that ability.

How Blue Can You Get?

WARP isn't color-coded in the same way as the radar you have or the radar the weatherman on the TV has. WARP's version of the weather is all shades of blue. Light blue is the heaviest precipitation; a medium blue with a sort of checkerboard pattern is heavy rain, and dark blue is moderate rain. It's weird when you first hear about it but it's not as weird as you might think.

As I said, this is one of the first color applications in ATC. Putting color onto a continuously updating screen isn't as easy as you might think. You can't have a datablock disappear just because it overlaps a thunderstorm. Ditto for airways, borders, airports, FACs and targets. I tried to do a little research in this area when WARP came out and all I learned was there hasn't been much research done in this area. Strange but true.

Heavy-Heavy

Speaking of strange, you might notice controllers stumbling around trying to tell pilots about the various intensities they see on WARP. That's because the three intensities are Medium, Heavy and Heavy. Yep. Two different "Heavy" intensities. The way that one was explained to me is that airline pilots have a different idea of what constitutes "heavy" than General Aviation pilots. The group that was trying to work all this out couldn't find a compromise so we wound up with two words to describe three levels. I still feel like a verbal klutz when I'm trying to describe the weather to a pilot on the frequency. "Well it's heavy but not really heavy. But that other stuff off your right is the heaviest heavy rain."

Only in America. Let me summarize all this technical stuff so we can get to the fun stuff. Center controllers now have two different weather radar systems, although most Center controllers now only use one of them. The one most use (WARP) is slow to update, so what you are looking at and what the Center controller is looking at might differ by several minutes. You might be in light rain but we don't depict light rain. We only depict moderate and heavy precipitation. And the other heavy. We do not under any circumstances depict/paint/show clouds.

If you're fortunate enough to have weather radar and you decide to compare notes with a Center controller on what he sees on the radar, don't be surprised if you find yourself talking two different languages. You might be looking at green, yellow and red, but Center controllers are looking at dark blue, checkerboard green-blue and light blue. And the reason I keep saying "Center controllers" is that Approach controllers have an entirely different system. So not only are pilots and controllers looking at different systems, Center controllers and Approach controllers aren't even playing on the same page.

Yes, my controller friends, I realize I haven't said anything about the various altitude stratums that WARP will depict. That's because I've haven't found it to be very useful. Airline pilots start deviating around the building clouds of a thunderstorm long before there's any precipitation to detect. Besides, one of the stratum filters has a software problem. I just run the one that depicts from the ground all the way up. That seems to work the best for me. Your mileage may vary.

The Blue Period

Thank goodness we're done with that. Let's get down to the real business at hand -- putting the equipment to work. The first thing to remember about using ATC services during thunderstorm season is that, despite all the techno-junk above, it's an art. Sure, we have millions of dollars worth of equipment pouring information onto our radar displays. But interpreting that information is an art. The question you need to find an answer to is this: Are you working with a Picasso or a first-year art student?

Controllers have to answer the question in reverse. Are we working a pilot with the judgment skills to match his sophisticated equipment, or are we working a student pilot on his first cross-country? Neither one of us has a choice about the matter. You aren't going to get a new controller and we aren't going to get a new pilot. We just have to get along with whoever we wind up with.

Controllers do try to hedge their bets. The ones who don't like vectoring student pilots around thunderstorms try to stick to the high-altitude sectors. There aren't many students in the Flight Levels. The ones who are more comfortable vectoring guys without weather radar around the storms (you don't ever get really comfortable doing it) wind up working the low-altitude sectors. Usually. Sometimes they get stuck. And sometimes you get stuck with the first-year art student.

Hearing Voices

Most of the time it's really not difficult for either of us to tell which one we've got. The aircraft identifiers tell most of the story for controllers. Boeings have radar and a professional crew. A Cessna 150 screams "STUDENT!" Everything in between can usually be sorted out after you have a little experience. The real judgment call comes with listening to the voice.

I'm not enough of a writer to describe how it works, but after a couple of transmissions I can usually tell what kind of pilot I'm dealing with. It isn't just what they say but how they say it. It's in the tone of voice. The hesitation or lack thereof.

I suspect the same is true for most of us controllers. Y'all can probably tell whether we're comfortable or not, too. If all you ever hear the controller say is, "Deviate as necessary," no matter what kind of pilot he's talking to, you'll have a pretty good idea how comfortable the controller is vectoring folks around thunderstorms.

Things Left Unsaid

There's a lot left unspoken between pilots and controllers when it comes to thunderstorms. We all recognize that we're playing with fire to some degree. We know that these are some of the most dangerous situations we handle on a regular basis, and none of us ever forgets that we're being recorded. That leads to some controllers clamming up and offering a minimum amount of assistance around thunderstorms. That and a lack of faith in their equipment.

As usual, I came to a different conclusion a long time ago. I figure if something bad happens the lawyers are as likely to come after me for offering too little assistance as they are for offering too much. I try to help out as much as time and circumstances will allow. I think I'm conservative in my advice, but I'll offer as much as I can. Up to a certain point, that is: Once the pilot starts doing stuff that (how shall we say?) shows a certain lack of judgment ... I can become as unhelpful as anyone you've ever met.

Taking that into account and the fact I promised you some war stories the last time I wrote an article on thunderstorms, lets take a look at some real-life examples. The normal text is what I remember being said. The parenthetical text is what was really being said.

There Once Was a King ...

There was this King Air inbound to Hickory, N.C., (HKY). I'd taken the handoff from Charlotte Approach and the aircraft was already in the heart of a line of thunderstorms before I ever got to talk to him.

"Atlanta Center, King Air 456 is descending to 4,000."

King Air 456, Atlanta Center roger, Hickory altimeter is 2992, say type approach requested. (Because every approach has a thunderstorm on it and I sure ain't picking your poison.)

"We'll try for the visual. Hickory is reporting VFR."

King Air 456, roger, report Hickory in sight.

It was about right here that the Mode C goes to "XXX" on my radar screen. That means the computer is receiving the Mode C, but it just doesn't believe what it sees.

King Air 456 say altitude.

"Ahhhh, we're level at 4,000"

(Sure you are buddy. That thunderstorm doesn't have anything to do with you sounding like you're in a helicopter does it?) King Air 456, say flight conditions?

"Uhhhh, we're doing okay. Heavy rain and we're getting bounced around pretty good." (We're in the middle of a thunderstorm and we're getting our brains beat out.)

The reason the Mode C went to "XXX" is that the airplane (and hence the Mode C) is bouncing around so much that the computer can't get a fix on what altitude the airplane is "maintaining."

King Air 456, roger, descend at pilot's discretion maintain 3,400. That's my minimum altitude (just in case you might need to know that) and you're cleared to deviate as necessary.

"Pilot's discretion to 3,400, 456."

King Air 456, roger, and you can deviate as necessary, there isn't anyone else out there. (Which really ought to make you wonder why you are.)

Sure enough, he broke out on the backside of the line and HKY was VFR. I bet he doesn't want to try it again, though. I don't either. I do fine creating ulcers for myself. I don't need any extra help.

And the Winner is ...

My all time favorite is the Sabreliner that shot the visual approach into a Level Five thunderstorm. Honestly folks, you can't make this stuff up.

The Sabreliner was headed into North Wilkesboro, N.C., (UKF), which is right up against the mountains. There was an ugly line of thunderstorms coming down from the northwest, moving east-southeast, just like normal. The first (and ugliest) one was only about five miles from UKF when the Sabre checks in.

"Atlanta Center, Sabreliner 123 is descending to 11,000."

Sabreliner 123, Atlanta Center, descend and maintain 8,000, the Hickory altimeter is 2992.

"Down to eight, Sabre 123."

Sabreliner 123, Atlanta Center, roger, be advised radar depicts a line of heavy precipitation approaching the Wilkes airport from the northwest. It's about five miles from the airport at this time, moving southeast and appears to be very intense.

"Sabre 123 roger."

Sabreliner 123, say type approach requested?

"Sabre 123 we'd like to try for the visual."

Sabre 123, roger, I don't think you can make it to the airport before the thunderstorm. (Just in case you can't figure out what I'm telling you.)

"Thanks Atlanta, we'll see how it works out."

Sabreliner 123, roger, descend and maintain 4,300, deviate as necessary.

"Sabre 123, roger, down to 4,300. We'll work our way down to the south and line up for runway 01."

So this guys maneuvers around to the south a little and keeps chugging along towards the airport. So does the thunderstorm. The leading edge (where the worst weather usually is) is now touching the edge of the field. When the Sabrliner is about 10 miles south he sees the field.

"Atlanta, Sabre 123 has Wilkes in sight."

Sabreliner 123, roger, verify you are still requesting the visual? (Are you really sure you want to do this?)

"Sabre 123, affirmative. We want to give it a try."

Sabreliner 123, roger, be advised I show the thunderstorm over the airport at this time, cleared visual approach North Wilkesboro (and best of luck to you, buddy).

"Sabre 123 is cleared for the visual at Wilkes."

I terminate radar, switch him over to Unicom and watch him until he disappears off the scope. His target disappears about five miles south of the airport (like normal) and the thunderstorm is now completely over the airport.

At just about this time, the National Weather Service guy shows up behind me. That's really unusual. They normally stay over in their work area unless something special is happening. He points to the thunderstorm over UKF and says it's a Level Five. I forget how the NWS ranks thunderstorms -- by height or rain intensity -- but it really doesn't matter. You don't want to be in one, regardless.

Sixty seconds later I hear,

"Atlanta Center, Sabre 123 is on a missed approach at Wilkes."

Uh huh. It doesn't really matter in this case that there aren't any procedures for a missed approach on a visual ... again, nobody else is flying anywhere near this thing.

Sabreliner 123, Atlanta Center, radar contact two northeast of Wilkes, climb and maintain 4,300.

"Uh ... Sabre 123, roger. Which way should we turn to get out of this thing?"

Sabreliner 123, Atlanta Center, climb and maintain 6,000, you need to go north or south, whichever way looks best to you, it's only about 10 miles wide.

"Sabre 123 roger, climbing 6,000 and we'll keep going north."

Sabre 123, roger. And congratulations. You're the first airplane I've ever worked to shoot a visual approach into a Level Five thunderstorm.

Yeah. I actually put that one on the frequency. I have a bad tendency to let my mouth get away from me. I can't explain why anymore than I can explain why some folks wind up flying in thunderstorms.

Last(ing) Impressions

I've managed to make it though 22 years without losing anybody to a thunderstorm. You don't have to look far to find someone who didn't, though. I still remember how small and short-lived the thunderstorm looked that caused the crash at Charlotte in 1994. The Southern 242 crash at New Hope, Ga., is still talked about in Atlanta Center. And that was back in 1977.

Thunderstorms are dangerous. Period. Stay away from them and you'll live longer. And so will I.

Have a safe flight.

Don Brown
Facility Safety Representative
National Air Traffic Controllers Association
Atlanta ARTCC


Want to read more from Don Brown? Check out the rest of his columns.