Radar scope 1968
22 min read
Aviation technology has changed rapidly over the years, and yet Air Traffic Control works much the same as it did during the booming 1960s. In this article from 51 years ago, Richard Collins goes behind the scenes at Washington Center to explore the technology at work, from flight plan routes to weather deviations. It’s a fascinating time capsule, and a reminder that the basics of IFR flying remain unchanged.

The System

The Center: Key to IFR operations

There are different ways to fly.  It is possible to go all over the country without calling anyone on the radio and without using “the system” in any way.  All it takes is an airplane, a compass, a map, and good weather.  This kind of flying can be made easier, or easiest, by using modern electronic equipment.  If the airplane is to be anything other than a good weather device, we need to know how to fly another way:  IFR, utilizing “the system.”  This takes an instrument rating, a lot of equipment, some savvy, and an understanding of the system.

Air Traffic Control is an enormously complex and expensive array of things:  towers, VOR’s, radar sets, computers, approach aids, and on down the list.  As complex as it is, the system is still a reasonably simple thing to deal with.  It is simple because everything is based on a personal transaction.  One man says to another:  “I want to fly from here to there, along this route, and at this altitude.”  Then a pact is made.  The pilot agrees to do exactly as the man on the ground says, and in turn the man on the ground agrees to keep the pilot separated from all fellow pilots flying IFR. That is all there is to it.

Air Facts June 1968

This article appeared in the June 1968 edition of Air Facts.

So, the biggest element in the system is still human—in two parts.  The man in the air and the man on the ground.  Neither is master and neither is servant.

To use the system we need to know as much about it as possible.

How does an IFR flight start?

When an instrument flight plan is filed, it gets its first real attention at an Air Route Traffic Control Center.  To research this we visited Washington Center. When you file IFR with an FSS they feed it to the Center on a teletype circuit.  As it is coming off a teletype machine at Center it is also being fed into a computer.  What goes in is your aircraft number, type, speed, departure point, proposed time off, altitude request, route of flight, and destination.  Some other numbers go in too, but they are for bookkeeping purposes.

The computer takes all this information and if it is digestible it is accepted and stored.  If something is wrong, the computer says so and the flight plan has to be checked and resubmitted to the computer.  This is time consuming because it is a manual process.


Why might a flight plan be rejected?  A fellow at Washington Center told us that 2/3rds of the rejects were because the flight plan wasn’t filed properly in the first place.  Maybe the pilot missed on an airway number, or used an even altitude going in an odd direction, or didn’t terminate the flight at an airport.  These mistakes are time consuming because they break the routine. If you have ever had a long delay on a clearance without an obvious traffic reason, could it have been because of a mistake in filing.

How about filing an IFR flight plan direct with Center, in the air, when it looks like one will be needed?

If a controller isn’t busy at all, he might take an IFR direct, but chances are he will have you call an FSS and file the complete flight plan there so it can come into Center in a routine manner.  If you do this, it might get back to the controller in a manner of a very few minutes.  Or, if Center is busy, it could take 15 minutes or even longer.  The moral is that an IFR flight plan should be filed 30 minutes before taking off, or longer, as the old dodge about picking up a clearance along the way if necessary just isn’t programmed in the computer.

Preferred Routes

Something the computer might do to a flight plan which doesn’t hold anything up is change a routing.  Preferential routes are published for busy city pairs but the computer has some additional ones for less heavily travelled routes, and it might change a flight plan accordingly.

When the computer stores an acceptable flight plan it applies the winds aloft at the requested altitude to the true airspeed and decides how long it will take the airplane to reach each point along the way. When all is finished the computer prints out a message that everything is OK, and sends a copy to the man in the Center whose job it is to deliver clearances.

Taxi, IFR

Radar scope 1968

When you are flying IFR the controller at his scope is your contact with the system. Each controller is responsible for a sector of Center’s airspace and controls either high or low altitude traffic. The small pieces of plastic on the scope identify aircraft.

As you start to taxi, the tower (or FSS) calls Center for the clearance.  If Center gives it to him with no restriction, then your release is up to the tower, or in the case of an uncontrolled airport take-off is at your discretion.

Take-off time is given to Center, and it is put into the computer which applies time-off to the information it has stored about your flight.  From this, completed flight strips are delivered to all concerned:  the controllers who will handle your flight, as well as other Centers which might be concerned.  On the latter, all Centers aren’t equipped for Computer exchanges of information.  Washington, for instance, has a direct hook-up with New York, Cleveland, and Indianapolis but not with Atlanta and Jacksonville.  The contact with these Centers is manual —a man with a telephone and a typewriter has to handle it.  Comparing the two systems says a lot for automation.

Somehow it had always seemed logical to us that Center would have the say-so on when a flight could take off IFR.  That isn’t really so unless there is a congestion problem. Center handles them as the towers launch them—up to a point.  When things start to bunch up Center can put restrictions on departures, and they frequently do this.  The day we were at Washington Center they had been having a congestion problem northeast-bound out of Washington National, so the man in charge of that sector put a 5 minute restriction on departures in that particular direction.  It’s 33 miles from National out to Leesburg, Va., where the Center is located, and you could almost hear the airlines screaming all the way out there.  A 5 minute restriction meant delays, but they don’t keep anybody’s timetables posted on the wall in the Center.


This is a good time to mention the atmosphere in the Center.  There they have the over-all picture.  They are all the traffic and all the problems.  When we are flying we only see our problems.  That’s probably the reason the man in Center doesn’t seem as sympathetic as he should sometimes.  He is running a system, we are just running an airplane.  In total, his responsibility turns out to be a great deal larger than ours.

When flying IFR, the first talking after take-off is usually with Departure Control.  This is not in the Center, it is at the airport.  If you took off from an uncontrolled airport out in the country your first contact after take-off might be with the Center.

It is the job of Departure Control to get you out to a certain point and up to a certain altitude, and then transfer control to Center.  Most controlled airports have airspace of their own.  That airspace usually extends up to 4 or 5 thousand feet.  The Center leaves it alone, and doesn’t fly anyone through it.


Clearance delivery 1968

This is the clearance delivery position in Washington Center. The computer gives all clearances to this man, and when you start to taxi out the tower, or FSS, calls him for your clearance. Then, unless otherwise specified, you may fly when ready.

When you are about to depart the airport’s air for Center’s, what’s called a hand-off is effected.  If you have a transponder, Departure Control will tell you to switch codes at some point, and in a moment he will give you a frequency and tell you to contact Center.  At the time he tells you to switch codes he’s telling the man at Center who will handle the next part of your flight where you are.  Your controller in Center will look at his radar scope and see two bright parallel lines about a half inch long and an eighth of an inch apart.  That’s probably you, squawking his code.  If you weren’t on a code he had selected on his radar, your transponder would only make one of these bright half-inch marks on his scope.


When you call Center, he’ll likely ask you to squawk ident.  When you do, your target will appear as one very bright half-inch long mark about a quarter of an inch wide.  He’ll have you in radar contact for sure then.  After a half a minute or so the target fades back to the two parallel lines. Looking at a radar scope for a while will really convince you of the value of a transponder.

When the Controller has identified your target, he’ll put your airplane number on a little clear piece of plastic and lay that over your blip on his scope.  As you progress, he’ll move the piece of plastic.

No transponder?  The same procedures apply, but radar identification is not as easy. Your position can be described to the next fellow along the line, and unless there are a lot of no-transponder aircraft in the area he can identify you pretty handily.  Still, he isn’t going to be totally satisfied until he can positively identify your target.  This can be done through a turn for radar identification, or by having you report over a station, with only one target over the station when you call.  An airplane without a transponder appears as a small dot on the scope.

The controllers say there is no real problem in handling aircraft without transponders.  After watching the scopes for a while, though, it was apparent that most aircraft flying IFR have transponders, and if they didn’t it would complicate things.

Once enroute, it’s simply a matter of flying from one controller’s segment to the next.  The hand-offs are simple within a Center.  A controller can even move to another scope for a moment and point and say: “That’s 95Y right there.” A hand-off to another Center, or to Approach Control as you near the end of your flight is like that first hand-off from Departure Control to Center:  a telephone and radar contact arrangement.


Washington Center 1968

Washington Center has four rows of controller positions, two of which are shown. The boards at the end of the room show current weather at most IFR airports in the area. The light and noise levels are low, and the atmosphere calm but very alert.

You might say that radar is flat.  If you had ten airplanes going the same direction on the same airway at the same point, separated by 2,000 feet vertically, you would have only one bright blip for all ten airplanes.  You can see how this would confound hand-offs, and you can see why they sometimes want transponders turned off, or set to low sensitivity. You can also see why some people sometimes say the radar/transponder system isn’t good because it has a limited capacity.

As a result of radar being flat, they have to try to space airplanes laterally so they can keep the blips (or blipps if you are transponder equipped and squawking the proper code) sorted out. See, Christopher, the world is flat after all.

That isn’t as restrictive as it might sound. All airplanes have to get down somewhere, and with the present air traffic situation the traffic in saturated areas all tends to go between two points.  So if the ten airplanes mentioned all arrived at the destination at the same time nine would have to wait anyway.  It thus doesn’t do utility a great amount of harm to send them down the airway one at a time.


The controller has flight strips close by his scope, and the airplane’s altitude is on these.  It’s also in the controller’s mind.  But, it isn’t on the scope.  He can sit back and enjoy his work if all the blips are separated.  When they get close together, though, he’s apt to lean forward and start making sure they are all at the proper altitude.  One fellow we were watching had a couple of blips on converging airways.  One was level at 6.0, the other was at 12.0 and wanting down.  He cleared the one at 12.0 to 7.0, but as they grew near he called the descending traffic and asked his altitude just as a double check.  It was 9.0 at the time and the controller seemed to like that extra bit of vertical separation as the blips merged on his scope.

All this is why it’s important to say your altitude when IFR, to be on it, and to be explicit in repeating altitudes to which you are cleared.  There is a requirement to report leaving an assigned altitude, but it is never a bad idea to also say the altitude you are headed for just to have it said again so that any possible error would have an extra chance of being detected. Example:  “95Y out of 9.0 for 3.0.”

Our Performance

Some of the controllers had some comments on the state-of-the-art in general aviation IFR expertise.

They like communications brief and correct. Some pilots don’t do a very professional job of talking or listening.  One controller said these must be new instrument pilots, but we doubt that is 100% true.  It would probably be infrequent IFR pilots who are occasionally overcome with the bumbles on radio.

They like for pilots to stay in touch.  A lot of general aviation pilots seem to turn the radio down.  Or maybe fly away from the station with the squelch down so that when the range increases the controller is effectively squelched.  They too often call and find nobody at the other end.  We heard some of that, too, and it’s easy to appreciate the frustration of trying to be a controller to someone who isn’t listening.

One fellow really sounded off.  He pointed at the big weather board at the end of the room (the weather was so/so—lots of rain around, visibilities 2 to 5 miles and ceilings 1,500 to 2,500 feet) and said people would even be out trying to fly around in Cessna 172’s in weather like that.

Discussion revealed that he must have once had a very bad experience with a 172 on an IFR flight plan.  There was ice in the clouds and the pilot got the ice and wanted a lower altitude which simply was not available.  The pilot must have let the airplane sag down through some lower altitudes without a clearance to do so, and we got the impression that it must have been one of those deals where everybody held their breath but it had a happy ending because nobody scraped any paint.

Anyway, this controller doesn’t like Cessna 172’s because of this, and you can see why.  The thing we wanted to tell him, but didn’t get a chance to because business in his sector picked up, was that there’s nothing wrong with a Cessna 172. The problem was in a pilot who bit off more than he could chew, and he would likely do the same thing in a Cessna 210, or 310, or 411.

Low Level

There is one important thing to understand when flying lower powered airplanes IFR.  The airspace owned by tower controlled airports was mentioned earlier. The fact that this airspace exists can sometimes create a problem if the only answer to ice, for instance, is a trip at low altitudes.

Two towers can shuttle airplanes back and forth on what they call “low-level” clearances without even telling the Center they are doing this.  Center isn’t allowed to use those low altitudes between tower operated airports. What happens if you want to go a long distance at a low altitude?  You usually can’t if the route would take you from one controlled field throughan area controlled by a tower, and on to a third controlled field.  They just don’t handle them that way.  You can go to an area on a low-level clearance, but often you can’t go through. This is something to check and understand for any given route if, say, ice is forecast above 5,000 and you are basing the practicality of an IFR flight on being able to fly it a 3,000.


The system is based on absolute discipline. In this regard, one controller said he had a vivid memory of last August.  It was a month of thunderstorms, and these caused them a lot of trouble—mainly with airline aircraft.  This controller said one pilot actually did a 360 in a Boeing 707 because of what he saw in front of him on his airborne radar.  Picture yourself with a bunch of airplanes all sorted out on a radar set and everything working smoothly.  Then, one of the airplanes makes a big circle instead of proceeding straight ahead at 500 miles an hour as he is supposed to.

Aircraft with weather radar present a problem because they sometimes detour without asking.  The faster the airplane, the bigger the problem.

Thunderstorm Avoidance

ATC radar 1968

Weather on traffic radar? The bright area just above the center of the scope is rain. The controller noted that we were interested in this, and about 15 minutes after this picture was taken he called and said to come take another. See below.

What about help from Center when trying to fly IFR in thunderstorm areas without airborne radar?  Many has been the time that we have asked a controller for a little advice about the weather up ahead.  Sometimes the answer is friendly:  “I don’t see anything bad up there, but my scope doesn’t show all the weather.”  Sometimes they just say:  “We can’t see weather.”  The answer you get is a direct result of the amount of pressure on the controller at the moment you ask it.

They can see some weather on their scope.  You will note in the picture that a rain area shows up quite brightly on a radar scope used for traffic purposes.  That rain was very heavy—we flew through it on the way home—but there was not one bump in it.  There was moderate rain over the rest of the area covered by this scope, but it was not shown.  Generally they can see the cores of fully developed thunderstorms.

When flying IFR, though, the worry is about turbulence, not precipitation.  The two are almost always related, but to really see, and tell, a weather radar is necessary and even they are not 100% guaranteed to keep you out of turbulence of the magnitude which might cause trouble.  After spending time at a Center, and after looking at the rain on the scope and then flying through it, we are more convinced than ever that it would be a foolish pastime to file IFR in an area with imbedded thunderstorms on the assumption that a controller would or could give steers around areas of turbulence.


The controller’s best aid comes from pilot reports. If he had a flight go through an area right ahead of you, then that pilot could pass on good information. Likewise he can ask airplanes with airborne radar for ideas.

One interesting comment from a controller came while we were looking at that rain area.  He said that airplanes without radar had been flying through it without a gripe, but that if we would stand there long enough an airplane with radar would come along and request a big diversion to go around it.

One aside.  They are putting in a new $15-million computer at Washington Center. From all it is going to do (including putting aircraft identification and altitude right on the scope) it sounds like a pretty smart gadget.  We asked Phil Ceconi, the man who took us through Center, about putting information from a weather radar into the computer and having it alert individual controllers to weather in their sector?  He didn’t say it was impossible.


Traffic delays.  The morning we flew down to visit Washington Center there were a lot of other IFR inbounds on the route and frequency.  As we all converged on Washington, the expected happened. Center started reading off holding clearances and all anybody could do was take them because National had just gone below VFR.  There were a couple of commuter airliners and a local service flight, along with a Beech, a Cessna, and 95Y.  As they went down the line, reading off the place to hold and an expected approach clearance time 45 minutes to an hour in the future, we awaited our turn.  It never came.  Instead, they cleared 95Y to descend to 4,000, and to contact Dulles Approach Control.

What caused our good fortune?

All the other airplanes were headed for the big hive, Washington National.  Our flight was to Godfrey (Arthur) Field at Leesburg, Va., a beautiful paved airport with a 400 & 1 ADF approach.  Even though we were headed for the Washington area and were being handled by the people busy with its problems, we were not subjected to the traffic problems.

We took this up with the fellows at Center, and they said that it was almost always possible to get into Leesburg, or even Dulles, with no delay even if National was backed up.  One added that virtually nobody ever did.  He said Leesburg wasn’t used IFR more than a few times a year, and he wondered why not.

Heavy rain radar 1968

Now heavy rain has increased in area. Moderate rain over the rest of the area is not shown. It’s possible to track transponder returns through the heavy rain area, but raw targets disappear. This rain was flown through about an hour later with no turbulence.

It would seem quicker to go into an airport with no delay and get a rental car and go to town than to hold for an hour for an approach to National.  This would be especially so if the trip was a typical one to Washington and would be scheduled to come back out at the evening rush hour.  When the Washington area becomes saturated it is generally really Washington National that is saturated.  The rest of the airports in the area are still accessible without traffic delays.  The same would go for departures.

Confused Computer

It’s not possible to pass up a chance to poke a little fun at a computer.

In that the airliners usually leave at the same time and go to the same place every day, their flight plans are automatically put into the computer at the appropriate time.  They call these canned flight plans.  As we were flying away from the Washington Area, IFR, we became aware of a great deal of confusion between Center and an airliner.  The airliner wanted J-61 and FL280, and Center had cleared the flight for Victor airways and a much lower altitude. Trouble was, the canned flight plan was for a DC-6, but there had been an equipment substitution and the flight was a jet.  The computer obviously couldn’t figure out how to get a DC-6 to FL280, and therein was the problem.  They got it straight in due course.

VFR Traffic

Maybe the next little bit is a controversial subject, but we were interested in hearing a controller or two on VFR traffic advisories.

One Controller’s pet peeve here was the length of time it takes some to get their message through.  If you do want VFR traffic advisories, say so right at first, as: “This is Twin Comanche 95Y for VFR traffic advisories.”  Then if they are busy they can say no and that can be the end of the conversation with a limited amount of frequency congestion.  Many pilots call and go through the whole routine of position, altitude, route of flight, point of departure, and destination and finally at the end say what it is they want.

VFR traffic advisories to us are good only in providing information on IFR aircraft.  The controllers only call traffic as they have time, so a pilot might be lured into a false sense of security when using this.  Pilots also might have the feeling that being in contact with a Center gives somewhat of a pseudo-IFR clearance.  As a controller at a different Center once related, it really shakes you when, after having a pilot on VFR traffic advisories for a while, he calls and says:  “It’s OK now Center, I don’t need any more advisories because I am VFR again.”

The Center business is the key to all IFR operations, and every instrument pilot, or pilot who is working on an instrument rating, should try to spend some time in a center.  FAA has a program now, Operation Rain Check, to familiarize pilots with the operation of centers, but if you can’t make one of these just locate the Center nearest you, call the watch supervisor and ask him if you can come in for a look at “the system.”  Seeing the other man’s problems and frustrations will help your IFR outlook.

Richard Collins
3 replies
  1. Larry F Baum
    Larry F Baum says:

    What a wonderful read. Richard always could make the complex straight forward. It’s quite amazing what’s changed in 50 years and what is pretty much the same. The only sad part of the article was reading about our former freedom to fly into and out of the DC area. DHS and FAA have done away with most of that in the name of security theater.

    Probably the biggest change for controllers is that virtually all pilots know precisely where they are and can navigate to any fix anywhere at a touch of a button or two. Controllers no longer have to worry about whether a pilot can pickup a distant navaid. Most IFR pilots also have some kind of on-board weather radar and virtually all ATC radars have weather overlays.

    And of course, Mode C radar gives ATC aircraft altitudes, Mode S essentially recreates the entire flight strip on their screens and ADS-B will do it all. The controller’s job isn’t a piece of cake by any means even with all the newer technology…busy terminal areas have a lot more traffic than they did 50 years ago.

    What’s exactly same are the communication issues Richard’s quotes from controllers about dealing with “ham voiced pilots” relative to readbacks and setting up flight following could have been written today.

    SKYKON says:

    I’ve always enjoyed flying in IMC since earning my instrument rating in the early 1980’s. It’s interesting to observe how little has changed regarding pilot/controller interaction since Richard wrote his article.

    What has changed and dramatically so – is new technology that has greatly enhanced the safety of IMC flight along with the suffocating complexity that has evolved regarding IFR flight training.

    It’s a real conundrum in my mind – the fundamental rules that govern effective partnerships (and thereby safe flight in IMC) between pilots and controllers has changed little over the past 50 years and yet complexity in the flight training arena has increased tenfold thereby discouraging wannabe pilots.

  3. WD ZAB & ZHU
    WD ZAB & ZHU says:

    I worked in ARTCCs back when we did everything “manually”. Hand-offs, point-outs, coordination .. etc. The computers have made the job MUCH easier … when I was a trainee, a 1,500 day was LOTS of traffic and the same center’s normal count exceeds 11,000 (the last I heard). Everybody now has a transponder, and I assure you that when T-37s were new in the fleet and they did NOT have X-ponders nor DME it was “exciting” since they flew high… in the middle of traffic.
    A great career, and I enjoyed 99% of it … never went to “WORK” a single day.

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