My friend Bob Poole (who has been advocating this for almost half a century) says it’s time to get it out of the sixties.
46 thoughts on “U.S. Air Traffic Control”
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My friend Bob Poole (who has been advocating this for almost half a century) says it’s time to get it out of the sixties.
Comments are closed.
Air traffic control works because it’s low tech. Turn off every erg of electricity and it continues to work.
It’s based on the principle of a bucket brigade. An aircraft on a flightplan (not all are) is not given a takeoff clearance until after it’s given a landing clearance. Which means, if the power then went out, they would be safe to both takeoff and land with no further contact with ATC. In reality, the first thing they do is revoke the landing clearance to an vortac orbit but that doesn’t change the fact.
IBM had a contract 30 years ago to upgrade the system and couldn’t do it.
Privatizing is a good idea, but it’s the skill of the controllers in their bucket brigade that makes everything work. I once turned the Seattle ARTCC upside down for a few days because I found a missing data point that resulted in a triangle of airspace many miles long that was technically uncontrolled for years with heavy jets constantly flying through it. While technically a safety hazard, because of the bucket brigade, in practice it was never a problem. Every aircraft, at all times has a responsible controller even when not in the airspace they are responsible for and are always handed off to another.
My Information Theory professor, manager of Communications at the Jet Propulsion Laboratory and coauthor of a textbook on Communication Theory, professed a number of beliefs that for some reason I wasn’t able to pursue further at the time and now can never follow up on account of his passing from this life upon being struck by a truck on the service road to the Foothill Freeway while commuting to JPL on his bicycle.
One was in the pre-Federal Reserve banking system that we had in the late 1800s, explained to be far superior to what we had, which at the time I was his student was the Carter-era “stagflation.” The second belief was that relying on GPS for any manner of aircraft guidance or separation was foolish, either from the ground as an instrument landing aid or from each other as collision avoidance system.
Given the peer pressure of politically correct thought, I was surprised that a faculty member of a major university outside of the University of Chicago would express to students, even over beer in the faculty club, such an openly Libertarian perspective on economic policy. When I asked about the various bank runs and financial panics of the late 19th century, you know, the standard narrative we have all been told and the boilerplate reasoning behind needing the Federal Reserve, he dismissed such concerns as overstated, stemming from a historical misunderstanding, or self-contained and self-limiting and not harming any depositor or investor who took due diligence regarding their money.
As to GPS, he dismissed it as not sufficiently reliable for either ATC or limited-visibility landing, but I guess I took his word for it and never pressed him on what was unreliable about it. Besides being a mathematician contributing to engineering theory, he consulted with Motorola, presumably having industrial contacts in-the-know on such things.
So what do those other countries know about GPS that we don’t know? Well people in other countries make all kinds of different decisions based on the available scientific and engineering state of affairs, now don’t they?
What I am suggesting is that the not-using GPS for ATC may not be simply that we in the U.S. are lazy or stupid or tied-in-procurement-knots — it could be that there are safety or reliability concerns against going in that direction? But then again, most people aside from cranks and the odd mathematical theorist turned communications engineer are perfectly OK with the Federal Reserve?
We are being lead by children that have no respect for historical knowledge. For example, the blockchain is a huge problem with digital currency that everyone seems to ignore.
Fractional banking is a risk factor that should be public knowledge allowing customers to choose between banks. Many would then choose a non-fractional bank, but so be it.
Getting rid of the federal reserve would not stop ‘printing money’ because all money is a loan of a sort, but it would decentralize it, making it more robust. You’d still have your occasional confederate dollar, but the federal reserve doesn’t eliminate that. We should put the control where it belongs… to the individual.
Caveat Emptor with full transparency.
GPS is used routinely in air traffic control. ADS basically just forwards GPS coordinates to the ground, and is used anywhere there isn’t a nearby radar to monitor the aircraft.
That doesn’t necessarily mean it’s a good idea, but it’s used over at least 80% of the Earth’s surface.
GPS is fine for the pilot, but the controller works in a different environment. They have to keep a thousand feet of vertical separation and 10 minutes of horizontal separation. That 10 minutes varies in distance for each aircraft depending on airspeed. Each controller has a zone of responsibility but also continues to control aircraft until handoff which can be before or after that zone. When a pilot requests a clearance it may require a clearance from an ATCS that isn’t in direct communication with the pilot or even the ATCS that is. In that case the ATCS request the clearance from a next in route controller who relays that clearance request to the next ATCS. The ATCS that issues the clearance does it back through the same chain of controllers from which it came. All the pilot knows is he asked for a clearance and got one back.
This is why after the breakup of AT&T the FAA became the 4th largest phone company in the country (since then they’ve gone back to contracting that. I worked for FAA, ANM TM&O when it happened.)
Interesting fact. It is very common for ATCS to direct planes into mountains in other controllers zones. It’s up to the othe controller to change their clearance.
Using GPS to control would have to overcome two problems. It’s not 100% reliable (and must be) but more important is it’s all or nothing. Currently ATCS do all the math required for their job in their heads on a fully memorized maps of their zone. They have to keep separation in both time and space.
The system works well. To integrate GPS into that would be a nightmare.
Most ATCS do not sit in front of radar screens. They sit in front of strip boards with flightplan info on strips of paper which they manually manipulated. The military uses radar to bring planes together which is why about 60% of military controllers are unable to become FAA ATCS.
Again, GPS is used routinely over most of the planet for aircraft to report their position to ATC via ADS. It probably does a sanity check with the IMU to ensure the GPS position is reasonable, and may fall back to that if GPS goes out. But most of the planet does not have radar coverage, and more and more radars are being phased out in favor of ADS-B.
Edward, you’re missing my point. Yes, GPS is used for positioning, but that’s not how you keep moving aircraft separate, ATCS also have maps of their zones, BUT THEY NEVER USE THEM. Maintaining separation is a very focused mental process, an ATCS has many aircraft and must keep a mental picture of the combined braided ribbons of each ten minutes into the future. Both radar and GPS exist but have almost no use in keeping aircraft separate.
Aircraft on a flightplan travel from point to point over a system of omni-directional vortacs, those are used for positioning, not radar or GPS because that’s the frame of reference controllers use to keep the mental big picture.
Only terminal controllers use radar which is a minor part of ATC. With the exception of major airports, ATCS don’t use radar. If an ATCS has a question about where a plane is, they ask the pilot to “report passing” a reference, either an altitude or vortac.
TRACON is different.
“Air traffic control works because it’s low tech. Turn off every erg of electricity and it continues to work.”
Every erg?
How does it work then..you have no radar, no radio, no GPS no VOR’s.
You got nuthin. It doesn’t work without electricity.
How does it work then…
As you can guess they try to get as many aircraft on the ground safely as they can and not give almost any departure clearances. All departure clearances must first have a landing clearance (which is always the case even if the pilot is unaware) which does not come from the controller the pilot is talking to (unless happening to land at the same departure point.) So a departing aircraft at that point is clear to both take-off and land with no further ATC contact. in practice, it doesn’t work that way usually but that is how it is designed.
Since I assume you are, from your other comments Gregg, a pilot, you should perfectly well know that towers have semaphore flags to communicate with pilots if all other means fail.
Re-reading te linked article it occurs to me how they can go about it.
I forget how many ARTCC there are, but I’m sure it’s less than a dozen. What they could do is carve out some low traffic zones from one of them (the Seattle ARTCC isn’t in Seattle BTW and controls WA, OR, Northern CA, ID, NV & UT and northern Pacific Ocean if I remember correctly.) Take the controllers that work Northern CA and assign them to a private company. It would be a lot easier to modernize that small company than to try to do every thing at once.
Revision, something I recently came across says they now have 21 ARTCCs That’s a lot. Not sure of the implication (which can’t just be more traffic because it hasn’t been that much more.)
Edward is correct. Ken is talking about something called procedural control which can be used in the absence of radar or GPS based surveillance. It requires greater separation between aircraft than what is permissible in a radar or ADSB environment.
Radar comes in two kinds. Primary radar and secondary surveillance radar. Primary in civilian use typical only goes out to 40 nautical miles or so and is almost useless as it doesn’t give altitude. For altitude of target you need to send the information from the aircraft to ATC. This done by adding an altitude code to the transponder code when the transponder is interrogated by a secondary radar. Secondary (SSR) goes out a long way depending on the local horizon.. The problem is the radars are expensive, need maintenance and are usually located on mountain tops. So when GPS came along the idea of aircraft simply sending out their GPS locations was a no brainer. ADSB (Automatic dependent Surveillance Broadcast) is what does this. There is still a transmitter in the aircraft along with a GPS unit and twice a second this information goes out along with a unique code for each airplane. All ATC needs on the ground is a receiver. This can also be done by anybody with some simple hardware and software. The latest iteration being tested is to use satellites to receive the data and transmit back to ATC on the ground which allows control even over oceans as well as aircraft tracking in real time (see MH370).
GPS seems pretty reliable to me and nowadays there is also the Russian Glonass, European Galileo, Chinese Beidou, Japanese QZSS and in the Indian ocean region and India the IRNS system along with the SBAS (Space Based Augmentation System sats which also function as extra GPS satellites. Currently here I have 41 GNSS satellites visible above a 5 degree mask angle (Search for a little app called GNSS View). Multi constellation receivers are readily available.
Australia hived off the ATC function from the regulator over 20 years ago. It doesn’t seem to have improved anything. US ATC is regarded world wide as being the best.
Mike, I also did coverage maps when working for ANM and there were lots of gaps. I worked both as an ATCS in OK and then ANM which is management and engineering.
It’s one thing to know of the technology available but quite another regarding how things actually work in practice.
What controllers do requires a unique mental focus. It’s not the guy staring at a radar screen you see at terminals, in the military or the movies.
When working, a bomb could go off behind an ATCS and they would hardly notice because they are so focused on their job. They don’t have time for extra information that they don’t need and they don’t need GPS. This is typical thinking of someone that doesn’t actually do the job thinking “GPS is great, we should use it.” It is great, just not fundamental to the job. It’s a distraction (where distraction is a huuge issue.)
This is also why the each plane works with exactly one controller at a time. While controllers may have over a dozen planes each.
In simulations 2 ATCS work together. One as the controller and one as all the simulated aircraft. The ATCS simulating a dozen or more aircraft has the trivial job.
During simulations they record the activity. The funny thing is, the ATCS imagines they are constantly talking, but in reality the tape is mostly blank punctuated with short clearances or requests. That is how focused their thoughts are.
Ken is talking about something called procedural control which can be used in the absence of radar or GPS based surveillance
What I’m talking about is what happens at ARTCCs which is where the meat of ATC is done. Those are nondescript buildings the public never sees but where the highest level ATCS work.
Procedural control isn’t some kind of backup to radar and GPS. GPS and radar are mostly unused in the real work of ATC.
At terminals they use radar, but that’s a minor part of ATC. Even then, they can operate without it (but not by choice.)
Radar is simply not useful in the actual work of maintaining separation. Radar is used mostly by the military to bring things TOGETHER! I have spent time with military radar operators while they worked.
BTW, bringing two aircraft together is trivial to keeping a dozen on intertwined 3D vectors apart ten minutes into the future which is why most military controllers can’t make the jump to civilian ATC.
It’s a fine idea to use GPS tracking for airplane navigation and to a degree for air traffic control. My main gripe with it for air traffic control is that you risk having someone flying with their transponder turned off. Or to have someone willingly pollute the air traffic control information with bogus positional data. You’ll always need to have radars or whatever to have a full accurate view of the air traffic.
As for the proposed new organizational structure the risk, to me at least, seem to be a less clear division of responsibilities. In the case that something like the 9/11 airplane hijackings happens once more who will be responsible to close off airspace and notify the USAF to enforce an air patrol?
I can kind of understand the US traffic control system is probably too antique and dispersed for any one vendor to be able to provide a complete working solution for it easily. It’s probably grown too large over the years to be easily replaced by any one software solution. In this case the proper solution is to simply define a standard for communicating and storing air control data, similar to the health care data transmission standards, or to the standards used in the EU to communicate EU trade, and then you can have multiple vendors provide multiple software solutions for each use case (which could be GPS positional data or radar data or whatever) and make them communicate.
Godzilla, when people think ATC they think radar when they should be thinking vortac. The pilot, not the ATCS primarily keeps track of vortac info. More accurately, they see the info from different perspectives.
I once held the check in my hand for a new radar installation. That’s the only time I ever touched a real check for over a million dollars.
“Godzilla, when people think ATC they think radar when they should be thinking vortac. ”
Complete and utter nonsense.
*IF* a person is thinking ATC then they should NOT be thinking VOR. They should be thinking radar.
VOR’s are navigation devices. They are used by pilots only, as you suggested. They are NOT devices used to control airspace—not used by Air Traffic Control.
I can take off from a non-towered airport and fly to another non-towered airport…use a VOR to keep track of my position…and so long as I don’t enter any CONTROLLED (as in AIR TRAFFIC CONTROL) airspace, ATC knows little about me, and simply cannot control me (AIR TRAFFIC CONTROL) even if they have me on radar (which oftentimes they do not).
Now on occasion (last Thursday for example) ATC will inform me of an aircraft it is not controlling and tell me what o’clock and altitude and what it’s doing. It doesn’t know anything about the type and – most importantly, it is NOT in radio communication with that airplane. That airplane is not being controlled and is not talking to ATC.
Furthermore – take last Thursday for example – I flew from the airport at Beverly Massachusetts to Syracuse NY and landed at Syracuse. I was under ATC all the time (at my request – Flight Following) and never – NOT ONCE – did I have anything to do with a VORTAC except to see if I could visually locate the Gardner VOR (I missed it — they are hard to see).
ALL without having anything whatsoever to do with a VORTAC.
VOR’s are transmitters and some airplanes have VOR receivers and by interpreting the needle I, as the pilot, can determine my bearing relative to the VOR. ATC has ZERO to do with that information and doesn’t see it. Doesn’t know if I’m using it.
You can fly a plane without a VOR receiver and still fly under ATC. (VFR).
To what do ATCS reference to give pilots a clearance?
Were you an ATCS Gregg?
Forgive my tone Gregg in my last comment please, much of what you said was perfectly accurate. Yes it is the pilot that sees the VOR which is why the ATCS can query the pilot and give clearances based upon it. You can also fly and ignore the VOR but you lose some of the service that ATC provides when you do that. When ATC tells you about traffic they see on radar they are simply being nice. It’s not part of their primary function and they are not required to provide it.
You will also note that when ATC gives you traffic information from radar it is less precise than an actual clearance. Now you should be able to guess the reason for that.
Let me qualify my statement, radar is more commonly used at terminals. Where they also do other things a bit differently. For example it is much more likely they will use airspeed for separation.
Gregg, do you ever fly IFR?
clear division of responsibilities
That’s actually one of the best things about ATC. It is probably the only job in the world where responsibility and authority are in perfect sync. If an ATCS is not authorized they are also not responsible, unliike every other job where the boss may have a different idea about that!
who will be responsible to close off airspace and notify the USAF to enforce an air patrol?
That would be unlikely to change under privatization. Whoever retained authority would simply notify the center.
Aside from the ability of the controllers the most used tool by ATC is phone lines. All radar and radio communication goes through them and it’s how the bucket brigade works.
No ergs then no phone, radar or radio communucations…second sentence of your first post.
That’s correct Gregg, but what I didn’t mention is they have a system to handle complete power failure (which means no ergs.) You fell into the trap of not being a charitable listener.
Also you will note that with power failure the phones (on a separate grid) often continue to work.
I did make an actual misstatement which I will leave as an exercise to the brilliant commentors here to find.
Ken,
I know a bunch of Australian ATC people. The enroute and terminal controllers sit in front of large computer screens displaying processed data (which may include position/altitude estimates from procedural control). The high altitude control and separation over the whole continent is done using ADSB and a network of ground stations giving coverage backed up by SSR radars in terminal areas. To file IFR anywhere you MUST now have ADSB in your airplane in Australia. Should the ADSB and SSR fail the system falls back to procedural control with drastic loss of capacity.
The only controllers who don’t have computer screens are the tower controllers at general aviation airports.
Pretty much everywhere nowadays airliners, bizjets etc which operate in the ATC system are also equipped with TCAS which works from the Mode C transponders in the aircraft. This is intended to be a last ditch defence against controller/system errors and gives warnings and escape maneuver commands.
There have certainly been changes since my day (flight strips went from monochrome to color) and there is more info available and now everyone has an information screen where there used to be just a flight strip board, but the fundamentals have not changed at all.
When a flightplan is filed all controllers get flight strips for their boards for their part of the plan which may include one or more strips for each flight.
Flight strips don’t have to be paper, they can be an electronic representation. Typically these were printed, but I’m sure some places use an electronic version. That electronic version could be a problem for some controllers because they typically put the stripholder on the board in a way to remind themselves they have an issue they must resolve after current issues.
They can have access to all sorts of data, static location data has VERY LITTLE to do with separation and is really irrelevant.
In a controller’s airspace you’ve got several things going on. You may have several airports. You have through traffic in all directions, traveling at speeds where slow 180 mph craft act like blockers. Departing and landing aircraft will conflict with through aircraft.
They never called it procedural control when I worked it because there was noting else.
You’ve got to understand what controllers do which has very little to do with the static position data that some systems provide and IS NOT USED by ATCS. For example, there’s no reason you couldn’t display the sector map in front of the controller. A good controller will ignore it because every detail is committed to memory and looking at the map is just a distraction. Similarly, they don’t need position data because it’s on the flight strip and it’s there job to constantly calculate updated positions which they do in their head and confirm by speaking with the pilot. More data is just redundant.
A controller is seeing something not represented on any display, anywhere. He/She is seeing ribbons going 10 minutes into the future for each aircraft entangled with all other current aircraft. The flight strips hold the entire amount of information that allows him/her to do this.
More information, no matter what kind or the source (radar, gps, or whatever) adds nothing to this ability and may actually remove essential focus.
Everybody has computer screens in front of them these days. Don’t let that fool you about what’s actually going on.
ATC happens in the heads of the ATCS. It’s not visible on any display.
Mike, I hope you understand I agree with your facts. I’m just adding perspective.
Mike, I’ve got a question about Australia. When I worked an ATCS was not allowed to work more than 4 hrs in an 8 hour shift and never more tan 2 hrs at a time (typically only 1 hr at a time.) What’s the rule in Australia?
Don’t know but I can ask next time I see one. I do know the computer systems “looks ahead” in time and warns of loss of separation or warns of imminent loss of separation.
Interesting. I’ve only seen the military version that only indicates when minimum separation is violated with no look ahead.
Mike, I thought of another way to try and explain it.
Why 1000 feet? Why 10 minutes? Those are arbitrary rules. More separation is probably safer. Less separation while less safe would allow for denser traffic. But whatever rules you choose you then have to enforce them.
Where all the aircraft are now, however you get the data, doesn’t give you that. It’s not a picture, it’s a calculation. Multiple, interacting calculations. Humans have a limited ability to do this so you don’t want extraneous information. It’s like being given a math story problem with a bunch of data that has nothing to do with the solution and you are only interested in the solution.
Flight strips give you the exact data you need to find solutions that fit these arbitrary rules without extra data that are not part of those calculations. However distant the aircraft are from each other now is not the important information. That’s too late.
A computer could probably replace humans; then you want all the correlating data you could get. Is that the goal? To replace humans?
Sometimes it’s better to stick with what’s proven to work. But I’m not the judge.
Just thought of another important aspect that should not be left out. ATC is a service. It is the pilots responsibility to know where they are and fly the plane. It’s not just the controllers that provide this service. Various radio assets at specific known locations and frequencies are an important part of this service. That’s what flight control is based on.
…Only if by “flight control” you mean control by the pilot.
Radio assets such as VOR stations are maintained by the FAA as, yes, a service. But ATC gets no data from VOR stations.
.ATC gets no data from VOR stations.
That’s a service to the pilot. ATC does however know exactly where those assets are and uses them to determine clearances. It’s sad to hear they are being phased out. I guess math is hard?
I wonder what the implications are? Although a clearance can be given to any point in space, usually ATC follow standard routes in their sector based on ground radio locations. Also an enroute controller could work their entire career and never adjust airspeed to provide clearance (although they could.)
ATC is fundamentally about numbers, calculations and clearance solutions. Not about pictures, but that’s what the public wants.
What I’m hearing from you folks is the bureaucrats won another where it’s about having their cushy fiefdoms… because it’s the opposite of both safety and saving money.
There was a trial ballon (?) which stated that the private system would be funded by user fees.
If I’m not mistaken, the AOPA is against that.
By 2020, all aircraft that wish to fly in controlled airspace must have ADS-B in and out. So the radar/GPS/ADS debate is moot. VOR’s are being decommissioned.
If you do not fly in controlled airspace, then you are not part of the Air Traffic Control System and therefore you don’t need a radio, VOR, GPS or anything if you don’t want to have it (not saying that is smart).
Automatic dependent surveillance – broadcast (ADS–B) is a surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked. The information can be received by air traffic control ground stations as a replacement for secondary radar. It can also be received by other aircraft to provide situational awareness and allow self separation.
Missing the entire point of what a clearance is. I weep for the future.
If 11 minutes from now all the aircraft in the sky were heading for the same point in space, that would NOT be an ATC issue. One minute later, it would be and appropriate clearances would be issued. ATC provides a moving 10 minute safety window where rules are applied so that no two aircraft are in conflict. Basically they look over the pilot’s shoulder.
Situational awareness is primarily the pilot’s responsibility so to the extent it helps the pilot that’s a good thing. But no pilot can be situationally aware of every aircraft for the next 10 minutes. That’s the service ATC provides. Current position doesn’t give you that.
To be explicit, ADS–B, radar and GPS don’t give you that. Which is not saying they are not useful.
I can’t speak for ADS-B, but having produced coverage maps for radar I can say they don’t come anywhere close to providing enough data for safety having huge gaps. I’ve experienced outages with GPS and certainly would not trust it. The basic fact remains that none of these technologies provide the service that ATC does.
Only if by “flight control” you mean control by the pilot.
To be explicit, yes of course.
This is an really important additional point. Just because ATC provides a 10 minute window doesn’t mean it keeps all threats 10 minutes away. A bad clearance can mean a conflict in seconds.
Knowing you are a safe distance from aircraft now, does not mean a conflict could not happen within seconds and the pilot not have time to react.
This is not something to allow neat technology make us complacent about. Fore warned is fore armed.
You could do the calculations yourself. How long does it take for two aircraft flying at 600 mph to travel a safe separation distance of 1000 feet?
The “periodically” is twice a second.
About ten years ago a simulation was done in western Europe using three times the normal traffic density of the already very busy area and “free flight” where all participants just flew direct where they wanted to go (saves fuel and time and money). There were surprisingly few conflicts and the simulation included air to air knowledge of other aircraft positions, tracks and altitudes and it was found that there was no problem with flight crews simply avoiding each other. The sky is big and airplanes are small.
A similar system called FLARM (GPS data re-transmitted and received) is used by sailplane pilots. Two sailplanes head at normal cruising speeds is the same problem as two 737s at 35000 feet at normal cruise when you calculate the relative sizes and speeds. Been there, done that and after evasive action we passed 3 seconds after sighting each other. FLARM came along shortly after.
The present ATC system is the product of inadequate technology and is based on what was available at the end of WW2.
You might be right. It would mean the concept of ATC as I understand it would go away.
Would it introduce a certain level of random hazard? I don’t know.
Are there any ARTCC ATCS out there following this post? A VFR pilot is probably unaware that most ATC is handled there and though my info is out of date, someone current on it would sure be helpful here.
I would like to make one final comment because I am exasperated.
ATC provides a service which not all pilots fully use or are required to use. They also provide services that are not central to their function. Pilots are most familiar with tower controllers which are a minor element of ATC. The primary function of an ATCS is to provide clearances than conform to FARs.
Position data, from any source or technology is totally insufficient to form a valid clearance. This doesn’t make the information useless, but it is insufficient regardless. Planes move. They cross paths thousands of times a day. They change altitude with every flight. This creates a conflict which is the primary service provided by ATC to resolve. But only pilots (or airlines) that choose to use this service do.
As Gregg pointed out, ATC does not receive VOR and the reason is because they don’t have to. They already know all the relevant data. It is simply a convenient reference to use with those pilots that can receive the data. It was news to me that they are being phased out, but I’m fully aware of their use and purpose. Other ways of identifying a 3D point in space and time are certainly possible but with reference to ATC I have no experience with them.
To follow up on Gregg’s reasoning where VOR info is known and therefore unrequired to be tracked by ATC. It is useful nav data for communicating with a pilot that can read it. Radar is sort of the opposite with a different problem. ATC has the data and the pilot doesn’t. So it can’t be used in a precise way to convey exact information to a pilot the way shared VOR data can. The ATCS would have to convey that precise info to the pilot by some other technology or just give imprecise info. They would never use that imprecise info as the basis of a clearance with the exception of an emergency where there is no other choice. Telling a pilot the position of another aircraft is a cutesy, not a clearance.
What else can I say?