# Subtelties in Controlling Air Traffic, from Chris Tucker

October 25, 2010 |

I've been thinking lately about some of the skills that have to be learned in order to work effectively as an air traffic controller and how they might translate into effective trading.

One of the toughest things to pick up seems subtle at first but must become second nature in order to ensure success. In order to illustrate this I'm going to ask you to imagine two aircraft. Aircraft A is traveling east along the top your computer screen, aircraft B is traveling northbound along the right edge. Our goal is to keep these two aircraft separated by at least 5 miles. The routes of these two aircraft will intersect at the upper right corner and we will name this location ZZZ. All things being equal, if both aircraft are the same type and traveling at the same speed over the ground and there is no wind, if they begin equidistant from ZZZ, they should arrive at the same time. Upon first glance, the two aircraft and the intersection form an equilateral triangle so one might assume, prior to ingesting the speed data, that they will be in conflict with each other at ZZZ. Now lets assume that aircraft A is a jet moving over the ground at 480 knots and aircraft B is a prop moving at 300 knots and they are both 25 nautical miles (nm) from ZZZ. After three minutes, Aircraft A will have traveled (8 nm/min * 3 min) = 24nm and will be 1 nm from ZZZ. At the same time, aircraft B will have traveled (5 nm/min * 3) = 15 and will be 10 nm from ZZZ. After 4 minutes, A will be 7 nm east of ZZZ and B will still be 5nm south. So they will not conflict with each other.

The point I'm trying to make is that at first glance, these two warranted some attention and some thought. In our lingo we would say that they looked "a little tight", but after a quick calculation, we can project into the future and see that they will not be close at all at the crossing point. Now add a 120 knot headwind to aircraft A and see what happens, now it is no longer perfectly clear that they will be clear of each other or "clean" in ATC jargon. Or perhaps make the wind out of the south southeast, accelerating Aircraft B and slowing Aircraft A. Or add some turbulence and now Aircraft A advises that he will be slowing down to dampen its effects. Or add a thunderstorm at ZZZ and try to guess what the two aircraft will do to avoid it.

So this idea of projection, of a vision into the future is critical. We cannot simply look at where things are, but where they *will be. *And then, we have to constantly monitor and check if conditions are changing and make adjustments as necessary. Our projections must be based on sound and rational expectations. I KNOW that if there are thunderstorms about, then there will be turbulence and I cannot expect any aircraft to maintain normal cruise speeds, I have to be able to adjust for that in my assumptions * before* it happens. My assumptions must take into account current conditions and projected conditions. Every assumption I make must be verified repeatedly to ensure that my vision of the near future is correlated with reality. If not I have to find out why and pronto. So being able to see accurately into the future requires some very thorough knowledge of aircraft characteristics, ie. rates of climb, speed in the climb and speed in cruise (sometimes radically different), knowledge of the airspace and procedures, current winds at various altitudes, weather, amount of traffic, and anything out of the ordinary. In the above sentence you can substitute any number of market phenomena and you come up with a similar picture. Granted, markets have many more random factors, but the idea seems to translate well.

The thing about a situation like this is that it is not immediately obvious what will happen. You have to do some calculating, some thinking in order to come up with an accurate projection. Situations may appear obvious at first but upon reflection may turn out to be entirely counter-intuitive. One thing about projecting is that it takes time for things to develop, you have to allow that time to pass in your mind to project and then allow it to pass in reality to check the validity of your projections.

It takes some exposure and experience to have confidence in your projections, to know the difference between what *might* work and what *will* work. And then to truly recognize what is working and what isn't. One of the things we try to teach people is, if a situation needs fixing, the most important thing is to do something, ANYTHING, right away. To make a decision, a choice, even if it is not the best choice, just make it and act on it quickly. Then let that guide you toward your next step. If the first choice was catastrophically wrong you will know soon enough and then you can use that information to change your plan. Continued exposure and experience will teach you how to make correct decisions more and more frequently. You begin to learn what doesn't work much more quickly than what does and tend to avoid those types of decisions. People who don't learn don't last.

A big key in the above is learning to be flexible. To not be so committed to a plan that you can't change it. You have to be able to allow yourself to be wrong or you won't be able to recognize the fact when it happens. When you learn to cut and run from your mistakes you find freedom in your ability to adapt. This tends to conflict with ego. Ego gets in the way, the truly great players have conquered their egos or at least don't let them interfere with getting things done.

High performance in any field also involves a willingness to try things, to tinker. And an ability to accept sage advice while picking and choosing the bits that fit your own style and discarding the rest. Unless you are truly capable of making anothers way of thinking yours, you will have to come up with your very own. Otherwise you will have no confidence in your decisions and when push comes to shove you will get steamrolled. Finally, you have to be willing to push. To go the extra distance, to surpass yourself. Again, if your ego is too big, there is no reason to do this. Lose the ego and the barriers that it creates vanish. Easier said than done of course.

Something important that I forgot to discuss: What happens when your expectations are violated? Here is an example from air traffic control.

Controller A tells the leading a/c (aircraft) to maintain 290 knots or greater and the following a/c to not exceed 290 knots. He does some other stuff, gets back to these two, sees that his plan is working (that is that the following aircraft is not gaining on the lead, which can happen, even when speeds are assigned, especially if the following a/c climbs faster as ground speed will increase with altitude at the same indicated air speed), then he notices that the lead a/c has crossing traffic at FL230 (Flight Level 230 is 23,000' more or less, another story) and asks the lead a/c to expedite his climb through FL240. Controller A then observes the lead a/c leaving FL240 and is no longer traffic for the guy crossing at FL230 so he issues a frequency change to controller B, who sees the assigned airspeeds in the data block and assumes everything is hunky dory. And rightly so, controllers must trust one another in order for the system to work. Then, as a few minutes go by, controller B looks again and sees that the following a/c has a 100 knot (groundspeed) overtake on the lead and is about to lose separation (5 miles is the minimum at this altitude). Controller B thinks "what the heck?" and asks the lead a/c his indicated airspeed and the pilot responds with "220 knots and accelerating".

Why is that? Well, controller A made a mistake but it is a subtle one, but one that all controllers should understand. When he asked the lead a/c to expedite its climb, he was asking for something that this particular a/c could not do while maintaining the assigned speed. So the pilot bled off airspeed and traded it for altitude, then when he left the required altitude he began accelerating again. In the pilots mind, the new instruction to expedite the climb superseded the instruction to maintain forward speed so he did that first and then went back to trying to go fast, which is difficult for this type a/c to begin with. The pilot sort of/kind of made a mistake by not informing the controller that the vertical maneuver would kill his airspeed, however I contend that controller A should have expected this. Controller B made a mistake by asking questions first and fixing it second. When we recognize an imminent situation we are taught to shoot first and ask questions later. The query ate up valuable time that could have been used to tear these two apart (not to worry, they did not get dangerously close).

A significant point is that it took time for the overtake to show up in the data. It takes five sweeps of the radar (one minute in most cases) for the tracking software to get an accurate bead on speeds, so the overtake was in place and the gap was closing before the data even presented itself. So when the speed is changing, the data will always lag by about a minute. This is why we have to understand not only how we should expect aircraft to perform, but also the limitations inherent in our systems. Its an important point, one that is not obvious and one that takes a while to sink in. So when your expectations are violated there is important information there that has to be sorted out and sometimes acted upon with alacrity.

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