Oh, And It’s Raining Again

(First post after some weeks of abstinence. Enjoy!)

“….requesting heading 330 to avoid weather”
“Who is requesting heading 330?!”

Welcome to my airspace. Available today: plenty of thunderstorms. If you order quickly, you get a free token for lightning, hail, turbulences and heavy rain. As a side-order, we recommend holdings over your favourite navigation aid, since your destination airport has just run out of usable runways (i.e. ones which are not flooded).

Special offer today: headings. Get them all, get them fast, following your normal routing is out of fashion and won’t land you any success with the girls.

And so it goes. Smack down in the middle of our airspace, the weather god (or the run-writer) has planted a CB. CB stands for cumulonimbus and is Latin for “Avoid me!” As a consequence, pretty much every airplane transiting through this area will request an altitude change or, more often, a “heading to avoid”, i.e. some way to get around the thundercloud.

For controllers, that basically means two things:

  • Try to maintain a picture when everyone is pretty much zig-zagging around the sky.
  • Work with much, much less airspace than you normally have, since half of it is full of hail (a redeeming feature? Hardly. The picture may be smaller, but it is much more complex).

One of the more interesting aspects of this is that we, as controllers, can only roughly see where the bad weather is (actually, in the Sim, due to technical limitations, it’s pretty accurate, but that’s got nothing to do with reality). The “clouds” we see on the screen are returns from our own ATC radar, which is limited to one fixed position on the ground. Put a few rain particles between it and the REALLY bad CBs, and you won’t see the latter. And of course forget about any direct information on where the clouds begin and end vertically.

The pilots on the other hand are at a clear advantage here. Most of them (pretty much all airliners at least) have weather radar installed in their airplanes, enabling them to see what’s in front of them, with pretty good accuracy both laterally and vertically.
Which basically means that the big picture about a pretty important user of our airspace (aforementioned CBs) is not with controllers, but with pilots – changing our relationship somewhat.

Since bad weather, especially thunderstorms, poses a serious threat to any airplane attempting to fly through, saying “no” to an avoidance request by a pilot isn’t really an option. The “control” in ATC thus reverts to an accepting of almost every request, while trying to still keep them all apart. When everyone has to be able to turn at any time he/she deems necessary, that can become quite a challenge.

The key to success here is vertical separation. If everyone has at least 1000ft between them, it doesn’t matter where and when they turn, there will always be separation (when someone requests vertical avoidance, that plan has to be altered somewhat, but as mentioned before this doesn’t happen as often as requests for headings).
Two airplanes at the same altitude just isn’t an option here (unless perhaps they are at opposite corners of your sector).

One other problem arises when everyone is flying on custom, hand-made headings – the next sector usually expects an airplane to arrive via its normal routing, not “25 miles south on heading 330 and once he is clear of the CB, he might actually turn back to his route”. Thus, that next sector needs to be made aware of the situation, so he can adapt to it.

And here comes the Planner. Busily handling multiple phone lines, preferably at once, he or she tries to make sure everyone stays up-to-date on the chaos we are throwing in their laps to work with. Actually, he trades that chaos with fresh chaos for our own sector, since thunderstorms have a habit of stretching around multiple sectors. It’s basically “trash comes in, trash comes out”.

How anyone stays alive on such a day is starting to become (hazily) clear after a week of this in the simulator, after being pretty much of a mystery at first.
A learning experience? You bet.

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