Computing & Air Traffic Control – Computerphile
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Computing & Air Traffic Control – Computerphile

In the old days air traffic control was .. didn’t really exist as such. An airplane wanting to fly from one place to another would just take off and would try to work out how to get to wherever it was going. Over time it was realized that we needed some form of air traffic control in order to more or less to avoid airplanes from banging into one another, but also to provide them with a service so they actually would know what the conditions were enroute and so on and so forth. So during the fifties and sixties what evolved was the idea of an air traffic control center where once the airplane was away from the environment of the airfield we now had a control center which would then manage the aircraft through what’s called the Airways system. And the airways is up at high-level, it’s once you’ve got away from the airport then you’re into the airways system. The next problem was how do we actually make all that work. Now, in the old days you’d literally have had a controller in sitting in front of the radar and assistants running around with flight strips taking them from one controller to the other, and that clearly wasn’t going to work in the longer term. Essentially a flight strip, when a commercial flight flies it files what’s called a flight plan and the flight plan says what the the flight intends to do. Where its going from, where its going to. What its routing is, what type of aircraft it is and so on and so forth. Quite a a lot of information and essentially that ends up becoming a flight strip which follows that flight around. By the mid to late 60s we started to try to introduce computers into this, effectively to coordinate the movement of air traffic and particularly to ensure that the controller had the information that he required, but also that the hand over between controllers, as the flights progressed, was done in a structured kind of fashion. By the time we get down to nineteen seventy we actually have a control room that’s at west drayton and what that was doing was providing control for everything in the airways system from the south coast right the way up to the Scottish border. There’s an equivalent one at prestwick which does Scotland and then basically pushes the aircraft out across the Atlantic. Each one of these hoods here is effectively a radar sector an area of airspace which is controlled by that controller. So what you’ve got here is a couple of controllers, the director who is overall in charge of that sector and effectively what’s happening is as the flight progresses it moves from sector to sector until eventually disappears outside of the British air control controlled airspace. One of the early attempts was to put in a computer called the myriad, this is around the late sixties into about nineteen seventies. It takes a long time to develop this sort of software and by the time the software had actually been developed so reasonably, so it was in reasonably working condition air traffic had increased to such an extent that the myriad was no longer capable of doing the job. In fact it wasn’t capable of even doing the civil job. It was originally designed to do civil and military. It was designed for fault-tolerant environments so it was a triplex system. Three computer systems effective they’re all three computer systems were doing the same job and what would happen is that an arbitrator would decide who got the right answer. Hopefully all three got the same answer but if they didn’t then it would decide which was most likely answer and basically two out of three was the arrangement. We were continually chasing up against the limitations of what the computer systems could do. The next attempt was really when it all started working which was in 1972 or thereabouts– the Board of Trade as it was then decided that it was going to go out and procure the 53rd, i think it was, air traffic control systems from the United States because they already had this sectorised control system using big IBM mainframe computers. The IBM 360 is the underlying machine behind this. 10 million pounds of equipment in 1972 ish there abouts for the first time we now have enough processing power – more or less to be able to do the job completely. What’s being pictured here is some of the initial testing that’s being done before the system went operational. Testing all of the various different conditions and making sure that if we did nasty things to a bit over here a bit over there, they didn’t fall over. That’s actually me running with one of the tests sometime in 1974 it would be. I’d come back from the United States where I went to the training course at the end of 73, by 1974 i was in there I was a bit younger and thinner in those days. Sean>What did it feel like going over to the States and learning that, was that a new thing for you? It was an extraordinary thing, i was twenty barely twenty-two when I went out to states and and I was basically a happy technician. It was like all my christmasses come at once. As a youngster who was interested in technology to have a 10 million pound computer at my disposal was just just extraordinary. We were actually encouraged to, particularly when we were on the training course, we were encouraged to write software. So i decided one of the things that I decide that try and do is to write a game where the computer played Monopoly and you can see here the high-speed printers these printers would run at six hundred lines per minute. And i wrote this whole thing in assembler the computer would make a move and it would then print the Monopoly board. So this thing was throwing up pages like mad and as the game progressed so the computer had to do more and more work and so everything got slower and slower. So it wasn’t quite throwing the pages at the same sort of speed. Everything was paper-based. This was before the days of VDUs, we didn’t have VDUs and things like that. This is the system control here. The system control is effectively the center of gravity of this entire system. What we then have is three compute elements which were IBM 360-65s, which in their day were quite powerful computers. They had behind them, get this, three-and-a-half mega words of memory, core memory, three-and-a-half mega words. Yeah they’re 32-bit words. so what would that be around about forty megabytes or something of that order of RAM. And we ran the whole of the national air traffic service on that without any problem. In fact we could run it on about three of them. We had seven storage elements and we could run with three, we prefered to have four so each one was half a mega word. Then behind there was three input output controllers which were IBM 360-50s now the IOCE, input output control element, was responsible for talking to all the various different pieces of equipment that are attached to this. So we have flight strip printers, radar systems, all sorts of things all feeding information in or receiving information out from the 90-20 and they were managed by the input output control elements which you can’t see they’re just behind there. The system actually worked for quite a long time in fact it was in service as this system itself right the way through til 1990 when it was replaced by 4381 computers, a quarter / a third the size and something like 10 times more powerful but essentially running exactly the same software in emulation mode in “360 emulation mode.” So this was still at west drayton. And really that was mostly done because this was quite old equipment even when it was first put in and so it was becoming too expensive to maintain. The skills and knowledge necessary to maintain it were effectively becoming difficult to find now. So that was the reason that was done and that kept things going right the way through really until the early two thousands when it became apparent that really what was happening now was that computing was moving away from the large mainframe environment to much more distributed architecture. By now we have networking, we have the ability to have mini and micro computers which is where they where we want them rather than having in them in a major computer suite. So really the west drayton environment wasn’t designed for that, it was designed with the idea of having central processing bays and lots and lots and lots of cables running underneath ducts under the floor to where they’re going to be used. In addition the RAF who actually owned the west drayton site they kind of wanted it back so there’s lots of reasons why eventually in the early 2000s we started looking at the idea of moving to a new control center. This is swanwick and effectively that completely replaced the west drayton setup. Interestingly however, some of the code which was written way up here back in the nineteen seventies is actually still in use to this day down here. A friend of mine who worked together with me on a lot of this software, going back to the early seventies, he said “hey you know I was I was kicking around in some code the other day, just looking at it” and he says “and I came across your initials against a line of code,” he says, “I thought about you.” So the thing is if this software still works it ain’t broke so why fix it. The problem of air traffic control is continually evolving but the core functions are exactly the same. It takes a long time to get it all debugged, so we might as well keep with the code that we’ve already got. However over time eventually that code will be replaced but it’s it’s a slower process. This was a major exercise getting this to work in the in the 70s so they’ve really sweating the assets and taking advantage of the fact that its extremely reliable code. We’d like to thank Audible for supporting computerphile and if you go to there’s a chance to sign up for a 30-day free trial and download a free audio book. The book I’d like to recommend is Ernest Cline’s Ready Player One. I enjoyed it so much I went off and downloaded his other book Armada as well, but ready player one is well worth checking out if you love the idea of a seamless VR system, dystopian future, lots of eighties pop culture references. I know a lot of people have been recommending ready player one. Its currently being made into a film so check it out and thanks once again to audible for supporting the computerphile channel. The other two canisters are actually butane cylinders which were discarded and they act kind of like a gas capacitor. They are called accumulators and they store gas close to where it comes out so that it can come out quickly


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