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
audible.com/computerphile 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
