Strip Marking

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Heh, heh—no one who knew me in ZJX is going to believe this post, and with the modern stripless ATC environment, it has little relevance to today’s controllers (although it should, as evidenced by a recent incident involving the computer loss of flight data). But back in the day, we used our flight progress strips as notepads. There is even a section in the ATP (Air Traffic Procedures, FAA Handbook 7110.65) devoted to strip marking standards. Part of the basic instruction I received long ago in Flight Data School in 1968 was strip marking. Most of it in those first six weeks centered around writing an original strip, unencumbered by any contemporaneous notes or markings which would characterize a strip after a flight had gone through a sector.

And we had these curious two-ended mechanical pencils, too—black lead on one end and red lead on the other. 99% of the time in Flight Data we used the black end (heh, heh—rereading this I’m reminded that the original lead in the black end was actually blue—after a week or so of use, the replacement leads available in the facility were indeed black). In that area the red end was used solely to mark the overflight symbol (a large Ο in the bottom right hand corner of the callsign box). However, on the boards, the red end was used quite a bit more. In general terms, red was used to write something which was tentative. In other words, if your planning included taking a flight off course (say for traffic) and then clearing him direct to a fix down the road which got it back on course, you would write the fix in red. Then when you actually cleared the flight direct, you would overwrite it in black.

If you asked a preceding sector to move a flight to another altitude to avoid hitting one of yours, the other controller would write the altitude on his strip in red, say “show it” (or “mark it”) to you, while he circled it (indicating the data had been passed to you, and you would write the altitude in black, because so far as you were concerned, that’s the altitude that the flight would be at when he entered your sector. We even carried that marking over to personal conversations—“hey, Roddy, wanna play golf after work tomorrow?” And he might say, “put it in red, let me check my schedule.” Later he might call you up and say, “that golf game? Black it in,” meaning the event had been moved from tentative to confirmed.

There were also other things. When an aircraft reported leaving an altitude, you wrote the altitude and then crossed it out. Simple. And about the only thing we did when we had an airplane in our sector was to put a big black “R” on the strip (as I recall, it went in the previous fix box to the right of the callsign box) which according to the ATP means radar contact. When you handed off the flight to the next controller, you circled the “R”. My recollection is we used that circled “R” to indicate we’d changed the flight to the next frequency (or “shipped him” as we were wont to say).

So, five years in the trenches, and skipping my ORD time, I arrive at ZAU and have to forget everything I know about strip marking. As I suggested in the first paragraph, my former ZJX co-workers would say that didn't take much effort. However, as Gordon Cooper said in The Right Stuff, “that’s a whole different ball game.”

The first thing I learned was to consign the black & red pencil I had brought with me to the archives drawer. There may have been a couple floating around the control room, but I don’t remember them. Everything was ball point pens—government issue, black ink, some retractable, most not. We still put anticipated clearances on the strip, as we did in red at ZJX, and circled it, when it was coordinated, but it was all in black, and until it was coordinated, we cocked the strip to draw attention to what needed to be done. Not as elegant as “national strip marking” as we called it, but reasonably effective.

Altitudes were another thing. First, in ZAU, we marked altitudes in thousands of feet instead of hundreds. Marking altitudes in hundreds necessitates a redundant zero every single time, which really didn’t make much sense, especially when holding, which we did a lot of, and was the driving force for much of the Chicago strip marking standards. Not using zeros was the easiest part of the ZAU Strip Marking Guide (yes, there was one) to assimilate.

Secondly, in national strip marking, when an aircraft reports vacating an altitude, you would draw a line through it—e.g. 60. That meant “out of six thousand” at ZJX and virtually every where else. At ZAU you showed a vacated altitude by drawing a line through the original and then writing the next available altitude below it (when descending, primarily, as virtually all holding involves descending aircraft). If a descending aircraft reported out of 6,000, you wrote down 5 as that indicated the highest altitude in use by that flight. It took quite a bit of mental gymnastics to grasp that, and I never completely embraced it until I got to the West Terminal where 95% of my holding experience accrued.

I hope I can articulate this properly. Let’s say you had a UA flight (246, let’s call it) in the hold at 15,000. On the strip you would see 15 in the altitude box at the bottom (at the bottom because the altitude on the strip when he came over to you from high was either his cruise altitude, or there was 20 (FL200) in the days when we staffed coordinators. When he leveled at 15, you wrote 15 at the top (and in place of any other altitude there which was then scratched out—single horizontal line drawn through it). At a glance, by you or anyone else around (D-side, hand-off man, coordinator, supervisor, etc.) it was clear that you had one in the pattern at 15,000’.

At some point you would clear him to a lower altitude as it became available—let’s say 12,000. You clear UA down to 12, simultaneously writing it in the bottom of the altitude box next to the 15, which you then scratch out. When UA reports leaving 15, you scratch out the 15 in the top of the altitude box and write 14 next to it. The premise is that all altitudes between and including the two un-marked altitudes are in use. Everything above the top altitude is available for use (as are, theoretically, the altitudes below the bottom altitude, although I never worked a holding pattern up).

Unlike anywhere else in the system, the altitudes in use need to be instantly recognizable when you’re in the hold, and an active number is the only way to clearly denote it. As soon as UA reports either out of another altitude or level 12, you write either the altitude he was out of or 12 on the strip at the top of the altitude box, scratching out the previous entry. The process becomes crystal clear if you look at a strip representing an aircraft who held and was subsequently cleared to every altitude from say 15,000 down to 7,000. First, on that strip—the last of that flight in the facility—we wrote in a contuous horizontal line, even spilling over into the succeeding fix box and the altitude box. When you looked at the altitudes on the strip, they would look something like:


15  14  13

15  14  13
 12  11

 12  11
 10  9  8  7

 10  9  8  7
If the unstruck numbers matched, top and bottom, everyone was safe. It was immediately and blaringly apparent if there was a discrepancy (an aircraft cleared to an altitude not reported vacated). Great system—probably lost forever.

Holding is probably the most dangerous aspect of ATC—I think principally because the amount of exposure to potential error (missed readbacks, for example) is so much higher when holding than in the normal enroute environment. It’s also essentially a non-radar function, and although separated by altitude, there can be six to ten aircraft all operating in a relatively confined chunk of geography, each a mere 1,000 feet from one another.

There was often an argument as to whether to terminate radar services when holding. Once we were fully operational with RDP (and discrete beacon codes) I never did. Others preferred to. My reasoning was that at some point I was likely to have to vector out of the hold (although ORD did it most of the time) and the added workload of notifying every aircraft that radar service was terminated and then re-notifying them when they were again in radar contact wasn’t worth the extra time—we were already busy enough. Besides, one of our functions in the hold was to watch for possible spill outs, and it’s much quicker to apply correction and separation to the offender without a lot of “how are you doing that if he’s not radar identified?” dialog, which contributes nothing.

Airborne holding is considered so dangerous, that the FAA spent a gazillion dollars and years of effort to develop a traffic management system, that while not very efficient and not always effective, reduces inflight holding by a substantial percentage—maybe 80%—from what we did in the ’70s. To me, it was an art, and an elegant art, but I’ve long since come to understand that what was art to me in ATC was either drudgery or risky by many others. People like me thrived on the model of ORD or the Common I (Common IFR Room—NY Approach Control). Others didn’t like what we were doing nor the prospect of doing more of it as volume grew. So it’s not done much anymore and more’s the pity, as there’s an entire generation and a half of active controllers who don’t have any idea how it’s properly executed. They just haven’t had the training, experience, or practice. I feel as if the system has been dumbed down, but that seems to be a direction society is following.

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Last updated: 03 September 2011