I am interested in authentication - how identity is verified - in civilian aviation radio transmissions. I know that when someone is speaking on the radio he tells his call sign. But is there any other system that verifies the identity of the person speaking besides just the call sign that he claims to have?

I am interested not only in how ground ATC verifies which aircraft is speaking, but also in how aircraft ensure that they are speaking to a real ATC facility.

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    $\begingroup$ @fooot No, because I am interested not only how ground ATC identifies which aircraft speaking but also how aircraft identify that who is speaking is real ground ATC. $\endgroup$
    – vasili111
    Jul 25, 2018 at 14:42
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    $\begingroup$ RE how controllers can identify aircraft: Controllers in busy airspace will often request an aircraft to "ident" immediately after their first call. On equipped aircraft, pressing the ident key sends a signal from the aircraft that causes that the blip for that aircraft to flash on the controller's display. This allows them to identify an aircraft. See this question for more on the ident piece $\endgroup$
    – Geoff
    Jul 25, 2018 at 15:29
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    $\begingroup$ @Geoff Anything similar for aircraft to identify valid ATC? $\endgroup$
    – vasili111
    Jul 25, 2018 at 15:43
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    $\begingroup$ @vasili111 not that I know of. Nav radios can be verified with audible morse code signatures, but comms are different. Theoretically anyone with a transmitting radio can claim to be a "controller" and there would be no way for a pilot receiving that transmission to verify. This is arguably rare though and would be caught and corrected immediately by the actual controller. $\endgroup$
    – Geoff
    Jul 25, 2018 at 15:56
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    $\begingroup$ One case worth mentioning here is Ercan ACC, which from ICAOs point of view is someone (turkish cyprus) setting up a full unauthorized ATC facility. No one is able to stop it because of the political situation on the ground. $\endgroup$ Jul 25, 2018 at 20:05

4 Answers 4


This is a reasonable question, and to an outside the simple answer of We don't / can't might seem a little bit jarring.

After-all, we live in a time of hacking, terrorism and so on and I can certainly see how this looks like a simple vector to create some havoc.

So, what's to stop somebody from setting themselves up with a Radio Transmitter and deciding to be Air Traffic Control for the day? Absolutely nothing. In fact, lower power handheld air-band transceivers can be purchased legally and cheaply by anyone. I have one near me - I could literally turn it on now and declare myself [Local Airport Tower]

However - the thing about Airband radio is that it's wonderful in its simplicity. At its core is AM radio which is basically unchanged since the early 1900's. This means a few things:

  • The strongest signal doesn't simply "win". Multiple medium strength signals will simply merge into a garbled mess. This means you don't simply get to "take over" ATC's transmissions - all you can do is ruin them.
  • Similiar to the above, there's no way (from outside) to stop the ATC signal. All you can do is stomp all over it - something which is totally noticeable.
  • Even if you do "win over" air traffic control for some aircraft, communications is a two way process, and airband radio is simplex. This means only one person can speak at a time - at some point ATC are going to key in.
  • Pilots aren't automatons. We listen and build up a picture, we learn normal procedures and can hear stress in somebodies voice. We also know who we were speaking to. Combined with a decent situational awareness, we don't just do things without thinking - you can't just pipe up on the radio and ask an aircraft to fly into the ground.

  • And even if you did, and they initially believe you, real ATC is going to hear your readback and ask what the hell is going on.

By way of analogy, imagine you've snuck in on a conference call between an employee and a boss. And you start trying to speak on behalf of the boss - it's going to last all of 1 second before somebody realises something is going on. I think people tend to think of ATC as somewhat robotic, but it's still a human interaction and any good pilot will understand why they're being given instructions.

To attempt to interfere in Air Traffic Control in a way that is believable by the pilots is going to be incredibly difficult. You won't be able to use normal phraseology and cadence if you're attempting to step on real ATC, and that will concern the pilot. To do that for more than a few seconds and to to cause some kind of conflict with multiple aircraft is verging on the impossible.

The most likely outcome is more a denial of service, rather than some kind of spoof. It's not really a great vector to cause any damage. A nuisance, certainly and absolutely dangerous (and there's a reason it's very illegal!) but there are well established procedures for disruption in communications.

I've focused primarily on somebody trying to be ATC here, which is the way in which somebody on the ground would likely go about trying to make a mess. As for pretending to be a plane - firstly there are more technical difficulties because you'll be transmitting Ground -> Ground. I live within 2 miles of my local airport and often struggle to receive their transmissions when I'm at home.

Pretending to be a real plane that currently exists in the sky poses the same problems as above and any facility with RADAR is going to know something isn't right. Again, it might cause some initial confusion but you're unlikely to persuade somebody of something.

You could, in theory, pretend to be a light aircraft with no (or a faulty) transponder but really to what end? I guess you could cause a little disruption before somebody realises you're having a laugh but we're more into the realm of 'pranks' (Not that it's funny) now rather than serious risk.

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Federico
    Aug 2, 2018 at 8:26
  • $\begingroup$ could you please add this some place to your answer: Radio Transmissions are very easy to triangulate even if you are only transmitting a short period. Certain frequencies such as any Air band transmission are going to get prompt notice from many people who have the capability of and motivation to locate your transmission point very specifically. $\endgroup$ Jan 14, 2022 at 3:47

So let's gloss over the technical details for getting a tower setup that is strong enough to reach far enough to really "drownd out" the proper ATC frequency. And keep in mind that while we are glossing over this, it's not the strongest transmitter wins, two or more transmitters would mesh and just make static and noise. But let's ignore that for now and say that got your setup working, and you're somehow, drowning out real ATC with your own signal.

First ATC is not in control of the plane, so if ATC asked a pilot to do something odd, the pilot can just refuse. There are very, very few instances where ATC has real authority. Mostly that authority is more like, yes you can enter this airspace, or no you can't. Media makes ATC (in movies) seem that it's in control and it tells pilots what to do. In fact, they are more of a service that makes sure planes don't smack into one another. That said if you ignore ATC you had better have a good reason because you're effectively ignoring the "thing" that is telling your X is safe and Y isn't.

Next, there are many "kinds" of ATC, and some of them have more communication with the pilot then others. For example, TOWER and APPROACH "levels" of ATC will talk a lot to pilots as it's their job to make sure planes are landing and taking off safely (glossing over a lot here). GROUND ATC is usually responsible for moving the plain around on the ground at an airport. CENTER level of control doesn't really talk to planes much, they're responsible for, essentially, all the space not around an airport, and generally, don't have much to do with the actual airplane. They don't sit around and go "Yeop your still ok, keep going that way." Though they can talk to planes it's usually to help them avoid other planes and to avoid weather.

Finally, there is the fact that there is a "normal" set of things each level of ATC may ask you to do. For example, GROUND will never tell you to change altitudes, TOWER only controls a very small space around the airport, etc. APPROACH and DEPARTURE may be the most "vulnerable" as they are the ones who handle making sure planes are not running into each other during takeoff and landing. BUT, every airport where it would be a problem has published SIDs and STARS along with approach procedures. So really all ATC does is say "Ok, you're not going to hit someone if you go do the published procedure". There are also published rules on how close planes can get to another. So again, even if you nailed the phraseology, you could not convince a small Cessna to get to close to a Airbus 320. As you stared to do things to move them close together, they would notice they're doing something wrong and refuse.

So while I suppose you could convince a pilot that you were ATC, all you could really do is actually do ATC's job. Not doing ATC's job correctly would just make the pilots go, "Umm, no"

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    $\begingroup$ A spoofed "United 123 cleared for takeoff" on a foggy day could certainly cause havoc, though. $\endgroup$ Jul 26, 2018 at 16:26
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    $\begingroup$ @200_success You'd need a really, really strong transmitter to pull that off, since the aircraft would be literally on the field right beside real Tower's transmitter in that case. As soon as you said that, you'd hear "United 123 Stop! Cancel Take-Off Clearance!" And then you'd subsequently be arrested. Likely on some kind of terrorism or attempted murder charge. $\endgroup$
    – reirab
    Jul 27, 2018 at 18:05

Not that I am aware of. Usual protocol when a call is initiated by a pilot:
who you are calling (Clearance Delivery, Ground, Tower, Approach, Center)
who you are/type of plane
where you are
what you want to do.

Example: Hanscom Ground, (who you are calling)

Nxxxxx, Cessna Cardinal (who you are and what type plane)

on east ramp with Information Echo, (where you are and that you have the local wind and in-use runway information)

ready to taxi for departure. (what you want to do)

Who you are calling will read back who you are (they may be monitoring more than 1 frequency and not always catch it all), and then proceed from there.

If you don't announce yourself to start the "conversation" you will not be granted clearance into controlled airspace.

  • $\begingroup$ But what if someone with radio transmitter will interfere in radio chatter, identify himself as ATC and will send commands to aircrafts? Is there any protection from this? $\endgroup$
    – vasili111
    Jul 25, 2018 at 14:47
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    $\begingroup$ No. Except real ATC talking and fake ATC talking will interfere and perhaps sound as a squeal over the headset, pilots will ask reply with "stepped on, say again" or something similar until they get a clear response that is along the lines of what expected directions are. $\endgroup$
    – CrossRoads
    Jul 25, 2018 at 15:13
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    $\begingroup$ Also 'fake ATC' would need a suitable transmitter, and if they want to be plausible to know real ATC procedures. And you can tall different voices apart on the radio. And fake ATC guy is going to be arrested and have the book thrown at them. $\endgroup$ Jul 25, 2018 at 16:40

Civilian pilots are identified and tracked in the same manner an any other pilot in controlled airspace - radio communications. Certain airspace (class E and G) do not require radio communications with ATC. If no flight plan is on file or activated, they will be unknown targets. Another means to identify aircraft are, enter establishing ATC communications, they are assigned a specific transponder code which then is associate with their radar returns, making it easy for controllers to know who’s who.

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    $\begingroup$ They can track airplane locations, but not the source of radio transmissions, as far as I know: >From an unknown aircraft waiting in a very long takeoff queue: “I’m f…ing bored!” Ground Traffic Control: “Last aircraft transmitting, identify yourself immediately!” Unknown aircraft: “I said I was f…ing bored, not f…ing stupid!” $\endgroup$
    – CrossRoads
    Jul 25, 2018 at 15:53
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    $\begingroup$ I dunno about ATC but ham guys can triangulate the position of a signal if it broadcasts long enough. $\endgroup$ Jul 25, 2018 at 16:48
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    $\begingroup$ Local ATC Tower/Approach won't have that capability, Center maybe. A lone plane flying along won't either. $\endgroup$
    – CrossRoads
    Jul 25, 2018 at 16:54
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    $\begingroup$ Re "Civilian pilots are identified...", that's really not the case at all. All ATC really cares about is targets, not who's flying the plane, or even that your tail number actually matches your call sign. I've occasionally given my own plane's number out of habit when flying something else, and nobody noticed :-) $\endgroup$
    – jamesqf
    Jul 25, 2018 at 18:11
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    $\begingroup$ @CarloFelicione The only way to triangulate is with access to multiple receivers, equipped with radio direction finding devices. In the UK. at least, lots of facilities can provide a bearing of a signal (E.g., it's coming from 070 degrees) but no single facility can provide a triangulation. There IS an exception to this, which is the UK's Distress and Diversion Centre who operate a network of radio equipment. But even that relies on the person being visible and generally doesn't operate at less than 1500-2000ft outside of London. $\endgroup$
    – Dan
    Jul 25, 2018 at 18:33

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