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Now now, settle down. Quiet at the back.

OK. Since I'm not an Air Traffic Controller yet, you might think the constant noding of subjects pertaining thereto is somewhat presumptuous. Well, yes. But since we don't have any real controllers here you'll have to take the rough with the smooth. The smooth being... iceowl, I guess.

So. These three words in the title. WTF?

We're well acquainted. You just know a primer is coming now.

Nodding again at paragraph two, my limited experience means that I couldn't say for definite what the worst words are that an Air Traffic Controller could hear. Or what the worst experience is. Although I expect the shrinking down of the picture on their radar screen to something the size of a postage stamp that slowly fades from view would probably be up there. Any students of David Gunson will of course be well prepared for such situations, as well as questions like "why do we need Air Traffic Controllers, anyway?" to which the obvious reply would be:

Well, yes, technically the reason is a bit hazy. The chance of two aircraft being at the same place at the same height at the same time, is so mathematically remote as to be not worth considering. All you do with air traffic control is to force them down very narrow corridors, thereby increasing the risk of collision. And thereby justifying the job of a controller to keep them apart.

In case of radar failure, the recommendation is to read the weather out over the radio. It doesn't matter where - Birmingham, London, Glasgow, anywhere. Just keep reading the weather, because as long as you're doing that none of the aircraft can get in and ask what's gone wrong. As an aside, some of the most irate controllers I've ever heard have got that way after a minute or more of some joker's stuck mic.

So, to business. Yes, the eponymous sentence would be amongst the least favourite sentences of a controller, though many have probably never heard it. I'm guessing "mayday, mayday, mayday," would be number one. Of course they're all consummate professionals, so you would never hear "what now?" in response to this.

IMC? Details are unimportant here - I'll simply say that there are two sets of rules under which aircraft can fly - Visual Flight Rules (VFR) and Instrument Flight Rules (IFR). VFR requires being able to see where you're going. Clouds are persona non grata. It's flight on a budget. Of course, as drizzled as the pancake of flight is with the maple syrup of legalese (if there is a less appropriate metaphor, please feel free to let me know), "being able to see where you're going" is formalised in a legal document. If your weather conditions fit within the provisions of said document, you are officially flying in Visual Meteorological Conditions (VMC). Otherwise, you're flying in Instrument Meteorological Conditions (IMC) and need to be qualified to fly IFR, as well as in a suitably-equipped aircraft.

The phrase of the title relates to formations. Every now and then—not often, but occasionally—a civil controller will have to deal with a formation of military aircraft. Maybe the Red Arrows/Blue Angels/<insert national display team> are transiting for a display, or some operational aircraft are using the civil route system to get to a training area. Whatever. The aircraft in the formation will always be operating under Visual Flight Rules; the respective pilots must be able to maintain visual separation from the rest of the formation.

Now, under normal circumstances, as long as all aircraft in a formation are within one nautical mile of each other, they are treated as a single aircraft by ATC, and the formation leader is responsible for ATC communications. For one thing, the aircraft will most likely be indistinguishable from each other on the radar display. For another, even if a controller became aware of any aircraft getting out of position, radar pictures are delayed by several seconds, so it would be too late to do anything. No, pilots in formations are responsible for not hitting other aircraft in the formation. The formation as a whole is separated from other aircraft by ATC.

Do you see where we're going yet?

Suppose the formation was forced into cloud for some reason. Yes, the pilots wouldn't be able to see each other any more. They would no longer be able to fly VFR. It would be impossible to safely maintain the formation. And you'd then hear the dreaded words from the formation leader:

"IMC. Split. GO!"

A mental "oh, shit" would quickly follow from the controller, as one radar contact blossomed into many and the formation members performed a predetermined split manoeuvre—although I prefer the more evocative "bomb burst"—to separate themselves from the rest of the formation. The controller then becomes responsible for:

  1. Individually identifying every aircraft from the formation
  2. Placing every aircraft from the formation under a radar service (that was previously being applied to the formation as a whole) and separating them individually from each other, and every other aircraft around them
  3. Giving traffic information about each and every aircraft from the formation, to all of the other aircraft in the vicinity from which they are now not safely separated.

Since their workload has probably just tripled, be a dear and make them a cup of tea when they've finished, eh?

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