the strips are your friend...if you use them

I'm out to inspire confidence.

Over the course of my training, which totals five months now and around 35hrs of controlling simulated aircraft, I have had three airmisses. An airmiss is the lingo-ish term for what is now called an AIRPROX (why the capitals, I don't know) and a "near miss" by most media. If separation - 1,000ft vertically or five miles horizontally - gets eroded, that's an airmiss. If two aircraft at the same altitude get 4.9nm apart, that's an airmiss. If two aircraft within five miles of each other get 980ft apart vertically, that's an airmiss.

Needless to say mine weren't 'real' airmisses or a number of you probably would have heard about them through various means. In summer 2000, when a trainee controller at Heathrow got a Boeing 747 112ft away from a 200-tonne bellyflop onto an Airbus A321 lined up for take off, most people knew about it.

One of my three airmisses happened on the last day of my first attempt at the training I am close to completing now. The other two happened about a month ago, during a particularly low personal point. All of them happened for more or less the same reason, other than that I was somewhat distracted during all of them.

I've already expounded on flight progress strips so I will just recap their purpose briefly as possible (though that node is decent background for this one). An ATC unit has paper strips for all the flights they are expecting. There is one strip for each flight, containing various information such as the callsign, aircraft type, requested cruising level and many other bits and pieces. The controller arranges them on a board in an order that gives an initial indicator of which aircraft may conflict with each other as they pass through that airspace. The strips for aircraft that are not yet talking to the controller are kept in 'bays' whose position on the board roughly corresponds to the direction from which those aircraft will enter the controller's airspace.

'Conflict' boils down to one aircraft getting in the way of another, usually vertically. One aircraft wanting to climb through the level of another when their estimated times overhead a particular navigation beacon are within a few minutes of each other, that sort of thing. The strips can be used to check whether a vertical plan is nominally safe. This is a slight simplification, but if you want to climb an aircraft, you just look at its strip and those that are above it on the strip board. If you climb it to 1,000ft below the level of the aircraft that is next above it on the strip board, you know that will be safe. If you want to climb beyond that you may have to use the radar to sort something else out, but again this is covered in slightly more detail elsewhere.

As the patronising, cartoonish poster hanging up in one of our classrooms says: 'radar can hide a multitude of sins; the strips can predict the future'. This is more or less correct, notwithstanding emergencies or other such unanticipated things. You can be too careful. When controlling we assume things are working as they should, but have plenty of procedures to invoke when they don't and have the law behind us in making such presumptions. Strips tell you what direction an aircraft is coming from and what direction it is leaving in; when it will reach a particular waypoint; what level it is climbing or descending to; they tell you what heading an aircraft is on. The controller uses that information to plan, and updates the strips as they give instructions to aircraft. Flight progress strips are also legal documents, tracing the controller's actions as they pertain to specific aircraft. If there is an 'incident', all of the relevant strips are impounded.

This is what would have happened after each of my airmisses, had they occurred operationally. All of them were caused by me failing to use my strips correctly. Here's one of them.

In the picture below I am controlling aircraft to the West of the transfer of control point. The dotted lines denote the boundary of the airway that the two aircraft are travelling through, which is ten miles wide.

                       Transfer Of Control point
        BAW969                    |
        160 E                     |                   AFR670
    . . . . *                     |                   150 W
                                  |                   * . . . .

This is all fine. The Speedbird (BAW969) is at Flight Level 160 (FL160 - about 16,000ft), 1,000ft above the Air France (AFR670) who is about to enter my sector at FL150. The Speedbird is on its way out, at its requested altitude. I don't need to do anything more with it, so as far as my inexperienced head is concerned I can get rid: I give it the radio frequency for the next sector and throw the strip away. It's gone, as far as I'm concerned.

Now, I spotted the Air France approaching about a minute ago, and have got the appropriate strip out of one of the 'pending' strip bays and put it into my 'active' bay in preparation. As you can see it is East of the transfer point, which would normally mean I cannot control it yet (aircraft frequently make contact before they have reached such a transfer point). However, we have a Standing Agreement with the neighbouring sector which says any aircraft coming out of that sector which is at, or climbing to FL150 when it makes contact can be climbed, descended or turned by us even if it hasn't reached the transfer point yet. I have also spotted, with some satisfaction, that this is the case.

This is the picture onscreen when the Air France calls me:

                    BAW969        |
                    160 E         |
                . . . . *         |           AFR670
                                  |           150 W
                                  |           * . . .

It is requesting FL250. As soon as he calls up I make a brief scan of the radar ahead of his track (like, forty or fifty miles ahead), look at my active strips and see there's nothing above him to affect him and, knowing he meets the standing agreement I just mentioned, clear him to climb to FL250. This is the picture about twenty seconds later:

                            160 E
                        . . . . *

                               * . . .
                               162 W

The two aircraft passed each other about two miles apart at the same altitude. If I didn't have my hand clamped to my forehead and eyes closed after my instructor asked "did you mean to do that?" I would have given avoiding action to one of them, and would have had to in reality.

As soon as we went 'clocks off' (ending the exercise) I pulled off my headset, sank back in my chair and laughed at the ceiling in horror at what'd just happened. "Jesus Christ..." My controlling had been flawless up to that point, only about two minutes from the end of the exercise. "A grade-A airmiss," as my instructor adequately called it.

Why did it happen? Because I'd failed to appreciate that the Air France wanted a climb that the Speedbird was 'blocking'. There were two chances I lost to catch this: first, I could have seen it on the radar. I didn't because I only looked for long-term conflicts. Air France wanted a 10,000ft climb after all, and would take a while to get up there. Still, I should have checked his 12 o'clock as well. That left only the strips to save the day and they couldn't because I'd thrown away the strip for the Speedbird. The result was a severe mistake: if a controller had an incident like that in real life they would be up before a Board of Inquiry at the very least, and rightly so.

Fortunately something like this is incredibly easy to prevent, which I learned from the two airmisses I had in close succession a few weeks back. The circumstances of the second were virtually identical to this one, just in different locations. If I'd just kept the 'dead' strip for the Speedbird in my active bay for another minute, the incident would never have happened. It would have been there for me to check when deciding whether to give Air France the climb it wanted, and I would have seen the problem. All I would then need to do was wait 30-45 seconds for the two to safely pass.

Now, before I throw a strip away for a transiting aircraft I always check it against pending stuff that's entering in the opposite direction; if there's a potential conflict there I leave the 'dead' strip in my active bay until the two aircraft have passed each other.

The other slightly less 'regular' situation in which the strips can save you (or rather, the aircraft you are responsible for... archiewood clears his throat) if you let them is that delineated elsewhere, in which an 'active' aircraft wants a change of level which does not conflict with any of the other active aircraft, but conflicts with a 'pending' aircraft.

My first technical loss of separation occurred during my first-ever summative exercise in August 2006. I had an aircraft entering my airspace from the East at FL130, exiting to the South-West. It wanted a climb to FL320. An aircraft was entering from the South-West in about ten minutes, maintaining FL290. I didn't even look at the pending strips, I just checked my active strips, saw nothing was in the way and cleared the westbound aircraft to climb all the way up to FL320.

A nineteen thousand foot climb-through, in a BAe-146. A lackadaisical and diminutive aircraft which probably has the lowest 'climb rate per engine' ratio after the Airbus A340, and is still used for The Queen's Royal Flight. I say we swallow our pride (pride? We dumped the VC-10 for a pissy little regional jet to carry our Head of State, for heaven's sake) and give Boeing some patronage, rather than just chartering triple-sevens from BA for transport of our executive. Concorde isn't even available any more - how mortifying.

But I digress, for a change. The aforementioned situation didn't get too ugly as I noticed the problem with the 'blocking' aircraft when it appeared onscreen, then stopped my BAe-146's climb short of it. But, if I'd simply checked my pending strips I wouldn't have issued the full climb in the first place, knowing how slowly the '146 climbs. A nice fat 'partly achieved' mark for the 'separation' and 'level instructions' objectives for that handiwork.

"Use the bloody strips," as I've been told by instructors a few times. Not recently, I'm pleased to report.

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