Further Adventures in Flight Progress Strips

Previously in air traffic control writeups: 1, 2, 3, 4, 5, 6, 7, 8...

Just kidding. This'll see you right. You might want some patience, possibly willpower, as well though.

I am writing this having been down, not out of the business for a couple of years now. Use this information to run an air traffic system at your peril, idiots.

So you've read flight progress strips, and thought you understood how air traffic control works. You might have thought you could do it with a bit of practice. You might have wondered what the big deal is, and why do they have you do three days of testing before they let you start training anyway. But what you didn't realise is how fucking wrong you were. You couldn't have possibly imagined that even with the false complexity shoved into the contrived system that I described before, that real life could actually be worse than training. That it could be the worst thing since Ishtar. It's at that moment, when you get up from your first Area Control sim, that you learn to never trust your own judgement again. To spend the rest of your life plagued with doubt and mistrust of everything, and everyone. You didn't realise that the nightmare of your own life had just begun. Well, don't worry. I'm here to help.*

Flight progress strips (the writeup) is all very well for contrived Approach/Area control bastardisations, but let's not confuse it with things that grown-ups do. Yes, the FPS work we've covered so far is kids' stuff. School's out.

How does it all 'really' work? How do those burnouts with no hair left that work at airports waving coloured bats around that haven't committed suicide before dying of old age and depression at 32 do it? It's simple. Well, maybe not, but in principle. A rickety wooden fence of simplicity poorly masking a grand canyon of complexity.

Whereas in previously we were looking at levels and the radar screen to work out whether planes were going to hit each other—and let's just point out that the usefulness of these two things cannot be overstated—here we're all about the estimates. The flight progress strips writeup doesn't even, like, have the word 'estimates' in it.

Before I continue I must apologise for the limitation-stretching ASCII art that is about to ensue. I'm only following orders.

Real-life en-route control (don't ask me about tower control or approach control in anything more than general terms) is based upon aircraft estimates, reported and requested altitudes and most significantly, multiple flight progress strips for each aircraft. In our previous example we had a single strip per flight, which moved around the strip board, symbolically following the aircraft as it flew through our bit of airspace. This is different.

Act I: Setup

First, the strips we used in the original writeup are grossly simplified, so we need a refresher/update. This is all from memory and I've omitted some excessive stuff, so again, no using this information to design an air traffic system. I've got my eye on you.

     1         2            3                 4              5

|   BLOK  | 170     |   AMERICAN   |                   | STAK 1057 |
|        /|         |     AAL45    |                   | R 310     |
|  39   / |         |     3654     +-------------------+           |
|10    /40|         |H/B767/S   450| KJFK T74 L45 EGLL             |

Ouch, eh? Let's go through the sections. Keep in mind that this strip is almost certainly one of several for the flight.

  1. Estimated time of entry. This says that the aircraft is estimated to arrive over a point called 'BLOK' at 10:39. The 40 inside the little triangle is the actual time it reached that point. The controller writes this number in (if they have time) after they see the aircraft blip at that position on the radar.

  2. The altitude of the aircraft. The initial altitude of the flight (whatever it's at when it enters the sector of airspace) is printed on the strip, and any subsequent changes are written by the controller. This aircraft is entering at flight level 170, or about 17,000 feet.

  3. Information about the flight. 'American' is the spoken form of the airline callsign, which is on the next line. 'AAL45' = "American four-five." The number below that is the transponder code for the aircraft. Usually though, on suitably-equipped systems the callsign is what will appear on the radar screen next to the blip for the aircraft.

    The bottom line contains the aircraft's vortex wake category (H for Heavy, in this case), the aircraft type (a Boeing 767), a code representing the capabilities of the aircraft's transponder (see radar for more on this, fact fans), and finally the flight's filed crusing speed (450 knots).

    This box is also where the controller squeezes in any heading or speed instructions they've given the aircraft. Headings are written to the left of the callsign, speed instructions to the right.

  4. Route information. This says that the aircraft is departing John F. Kennedy International Airport (KJFK) and flying to London Heathrow Airport (EGLL) via the airways Tango Seven-Four (T74) and Lima Four-Five (L45). The big space is for the controller to write notes about the flight - for instance, what runway it is being vectored towards.

  5. Estimated time of exit. This says that the aircraft is estimated to arrive over a point called STAK at 10:57. It also says that the aircraft is requesting to cruise at Flight Level 310 (R 310).

A similar strip will mark the next point on the flight's route:

|   STAK  | 170     |   AMERICAN   |                   | DANI 1108 |
|        /|         |     AAL45    |                   | R 310     |
|  57   / |         |     3654     +-------------------+           |
|10    /57|         |H/B767/S   450| KJFK T74 L45 EGLL             |

Compare it to the previous one - STAK now appears at the 'beginning' of the strip, on the left, and on the right we can now see the next point on the flight's route: some place called DANI.

OK, fine. But before we can proceed to Act II, I need to establish a fictional bit of airspace.

MAZR +--------R17--------+--------R17--------+ GRAF
DEMO +--------N86--------+--------N86--------+ LOCK

All the names are reporting points, that aircraft passing through the airspace use to plot their routes. We have three airways: L45, R17 and N86. L45 is for North/South traffic. R17 is for eastbound traffic, N86 for westbound.

Ideally, the board in front of the controller that holds the flight progress strips would be some kind of symbolic representation of the airspace, so the position of each strip roughly represents the position on the screen the controller looks at. Most likely they'd be arranged in three columns, with separators in each column acting as a header of sorts for each reporting point.

OK, now we're ready. We've seen the gun.

Act II: The Challenge

If you think I'm ASCIIing a strip board you're in cloud cuckoo land. Instead, I'll present you some strips.

|   MAZR  | 310     |    UNITED    |                   | ENDR 1102 |
|        /|         |    UAL135    |                   | R 310     |
|  57   / |         |     3614     +-------------------+           |
|10    /  |         |H/B767/S   450| KJFK R17 L45 EGPD             |

|   LOCK  | 120     |   SPEEDBIRD  |                   | PETR 1055 |
|        /|         |    BAW003    |                   | R 600     |
|  51   / |         |     4372     +-------------------+           |
|10    /  |         |H/CONC/S  1330| EGLL N86 KJFK                 |

|   BEAN  | 170     |    FEDEX     |                   | PETR 1059 |
|        /|         |    FDX04A    |                   | R 310     |
|  53   / |         |     6512     +-------------------+           |
|10    /  |         |H/A310/S   420| EGHH L45 EGPF                 |

That's the last of the intricate ASCII art, I promise. Let's break these down.

  • First up is United 135, a Boeing 767. Look at the start/end points, and the routing. You can see he starts at MAZR, goes eastbound along R17, then joins L45 at ENDR. Going North or South? Since he's going to Aberdeen (EGPD), we can safely surmise it's North.

  • Next: Speedbird 003. This is a fancy-pants Concorde going West from Heathrow to JFK, along N86. Check out the insane cruising speed and altitude. Next!

  • Fedex 04A is an Airbus A310 going from Bournemouth International Airport to Glasgow Airport. Starting at BEAN she heads north along L45, towards PETR.

So, extrapolating from the information there, we will have three strips for UAL135 and BAW003, and four for FDX04A. Each one has a strip for where it enters and exits our airspace, and another strip for every reporting point they cross while they're in it. UAL135 and BAW003 cross one other point. FDX04A crosses both PETR and ENDR on its way North. The strips are arranged on the board, categorised by reporting point, with the strips for every reporting point arranged in level order (the one thing we take from the flight strip method I showed in previous writeups): the aircraft with the lowest altitude is at the bottom of the pile.

The strips don't quite have all the information we need, but I've exhausted as much of my resolve as I have the patience of my readers in pasting this many strips, so I'll just add the following: our fourth strip for FDX04A has it estimating ENDR at 1100. The third strip for UAL135 has it exiting at ALAI, so it's heading north.

Aside: writing this has really increased my respect for the poor saps who have to design these ******* simulator exercises.

Let's go through them again, looking at what action they need.

  • UAL135 doesn't need any attention. It's merrily following its planned route, and you can see from the strip that its actual level is the same as its requested level. It needs nothing from us controllers. Noders. Notrollers? Trolloders? But this is a planned simulation, so it must be there for some reason.

  • BAW003 wants a climb. It's entering at Flight Level 120 and wants to climb, ultimately, to FL600 (about 60,000ft). It's also going to want to put the hammer down at some point, but that's by the bye.

  • FDX04A also wants a climb. Starting at FL170, it wants to climb to FL310.

Do you see any problems, here?

Act III: Resolution

The basic ATC method is to scan through the strip board, one reporting point at a time (in whichever order works for you, I guess), looking at each strip and asking ourselves three questions about that aircraft (please excuse my gender pronouns):

  1. What does he have?
  2. What does he want?
  3. What can I give him?

Maybe an aircraft wants a climb and we haven't given it yet, or have only given part of it. Maybe the aircraft is approaching the edge of our sector and we can dump it onto the next guy. Maybe the aircraft is locked onto a heading, in which case we'd ask if it can resume own navigation. OK, that last one's as much for us as it is for them.

Let's now go through the scan. The order in which the reporting points are scanned is really the controller's preference, so bear with me:

  • First reporting point we check is MAZR. All that's there is the entry strip for UAL135. That one's already entered and has passed MAZR, so we can throw that strip away. No other strips remain under this reporting point. Next!

  • ENDR. We've got two strips here, because two aircraft cross it: UAL135 and FDX04A. Their strips are arranged like this, boiling down the essential information (callsign, flight level, requested level):

    UAL135 310 R310 1102
    FDX04A 170 R310 1100

    We scan from top to bottom. UAL135, as we've established, doesn't need anything. FDX04A, however, needs to climb 14,000ft. Can we give it? Nominally, no. UAL135 is in the way. This is when we look at the estimates. Are the two aircraft going to be at ENDR at the same time? UAL135 estimates ENDR at 1102; the Fedex at 1100. That is close enough that we would need to look carefully at their positioning on the radar, maybe switch on the vector lines to see their projected positions in a few minutes' time. UAL135 is what trainees call a 'blocker'. Well it has an 'er' on the end, anyway. If an aircraft is slow, and/or enters your sector without needing anything from you, you can guarantee it's there to get in the way of something else.

    The initial, minimal-effort solution here is to climb the Fedex up to FL300 underneath the United and deal with the last 1,000ft later. Can we do that? The Fedex has only just entered our sector at BEAN, so we need to check the other reporting points it's passing, and make sure nothing is in the way. So we have a peek at the strips for the PETR reporting point:

    FDX04A 170 R310 1059
    BAW003 120 R600 1055

    We're fine. Concorde is underneath the Fedex, and he's four minutes ahead anyway. We climb FDX04A to FL300 and mark all of its strips.

  • Next we check out the reporting points for ALAI, GRAF and LOCK. ALAI just has the exit strips for FDX04A and UAL135. We've just given the United the best climb we can for now, so move on.

    Nothing is at GRAF, and all we've got at LOCK is the entry strip for BAW003. He's already passed LOCK by this point, so we throw the strip away. Next!

  • We're back at PETR again. We've got the Fedex and Speedbird. Fedex wants FL310, and is just beginning a climb to FL300. Speedbird wants FL600. Can we give it? If he was much later arriving at PETR the answer would be no - we'd have to step-climb him up underneath the Fedex and keep checking whether we can climb him further, because aircraft don't like levelling off during a climb. However, he's over PETR well ahead of the Fedex so he gets a nice juicy 42,000ft climb. Again, we mark all of the strips for that aircraft with the climb instruction.

  • BEAN. Nothing to see here.

  • DEMO. This is the exit point for BAW003. We've given him everything he needs, so we're bored of him now, and are just waiting for him to get near the edge of our sector so we can get rid.

  • Aaand we're at MAZR again. Back where we started. That whole process took less than 20 seconds, by the way.

We'd now go around the board again, eventually get a bit more intimate with the United and Fedex and put them on parallel, or diverging, headings so we can climb the United up to the same level. We would also need to let the adjacent sector know that we're presenting the aircraft to them like this. It might be that this is no good for them, and we'll have to do something else.

There. You now know how to do a real strip scan. The next time you're visiting your local TRACON and one of the controllers keels over...well, a relief controller will be there to replace them. But you could totally do it too. For real.

<<Lesson #4

* Yes, I stole the opening from a certain Youtube review.

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