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Usually, when the aircraft enters a new flight information region for example, ATC will ask the pilot to enter a new frequency. I'm curious about when they do. Is there a rule about it (in an IFR situation)? I assume it may be different between EASA and FAA regulations.

Thank you.

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    $\begingroup$ I don't understand what you're asking since you appear to have answered your own question. As an aircraft moves from one area of responsibility to the next the controller hands off communications to the next controller. This seems obvious to me. What 'rule' do you expect to find? $\endgroup$ Apr 20 '20 at 8:24
  • $\begingroup$ Well, I don't think that it is that simple in my opinion, someone should confirm it but maybe ATC have to anticipate this kind of event, to prevent a frequency change error from the pilot for example. I don't believe that they inform the pilot just when they "cross" the new area. $\endgroup$ Apr 20 '20 at 8:35
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    $\begingroup$ @FlyingRandomGuy They do - a combination of readback and use of names prevents errors. Pilots should know their route and who they're going to be talking to, so the new frequency shouldn't be a major surprise $\endgroup$
    – Dan
    Apr 20 '20 at 9:17
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The entire sky and all airports are divided into ATC areas of responsibility. Whenever a flight moves from one area of responsibility to another, the pilot needs to change frequency to talk to the next controller. A flight can only be under the control of one single ATC unit at any one time, which usually equates to being on one single radio frequency. When under ATC control, pilots do not change frequencies unless instructed to do so.

For the en-route phase, airspace is divided into sectors, defined as three dimensional areas. Each sector will typically have its own dedicated frequency, although sectors can be combined in which case several sectors may operate on the same frequency.

On the ground, depending on the size of the airport, there can be multiple different frequencies. It is common to have one tower frequency per runway, and then one frequency for the taxiways - or possible several, if the airport is large and complex.

ATC will instruct the pilot to change to the next frequency at the latest when the flight enters the new area of responsibility, and often a minute or two before that. At that point, the flight will already have been coordinated between the controllers, so the controller of the downstream area of responsibility knows it's coming. Specific rules for transfer of communication is agreed between adjacent ATC units in letters of agreement.

An example from Copenhagen: enter image description here

AIP Denmark EK AD 2 - EKCH - AREA OF RESPONSIBILITY

Each color depicts an area of responsibility, and (this is a bit simplified but) essentially one specific frequency that pilots should be on when they are within that area. You can see that each runway (roughly) has one frequency, and the apron area where aircraft park has another. When taxiing from one area to another, the controller will instruct the pilot to change to the next frequency.

In the air, it can look something like this: enter image description here

AIP Denmark EK ENR 6.2 - 3

The dashed lines indicate borders between areas of responsibility, and the bold text indicates the frequency to use in that area. Again, the controller will instruct the pilot to change to the next frequency when crossing from one area to another.

Further reading

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    $\begingroup$ Thank you for your interesting answer. $\endgroup$ Apr 20 '20 at 9:58
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    $\begingroup$ @FlyingRandomGuy Welcome to Aviation.SE =) Thank you comments are discouraged on this site. Instead, please consider up-voting the answer. $\endgroup$
    – Bianfable
    Apr 20 '20 at 10:11
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The controller will request the pilot changes frequency either when the controller is ready for them to do so:

G-ABCD, Contact Anytown Control 123.000

Or, they can request change at a particular moment, for example:

G-ABCD, at Waypoint Contact Anytown Control 123.000

or

G-ABCD, when passing FL100 contact Anytown Control 123.00

That's it really - there isn't some huge preamble or discussion.

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In IFR flight the ATC controller will not tell the pilot to change frequencies until he has coordinated with the next sector. The next controller must check for conflicts before he can accept a new aircraft to his sector.

More and more this is done through Controller–pilot data link communications (CPDL) text messaging and no radio call is needed to tell the pilot to change frequencies.

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Other answers have addressed where and why but perhaps not how or, as you asked, when. I'll answer that for FAA-land.

The transferring controller must transfer radar identification of the target before entering the receiving controller's airspace (for VFR aircraft) or protected airspace (for IFR aircraft, i.e. 1.5 or 2.5 NM from the airspace boundary). The process for transferring radar identification is spelled out in the 7110.65 chapter 5 section 4; you can do this physically (go to their scope and point at the target), using automation (enter a command to "flash" the target on their scope), or manually (call them and advise of the target's position relative to a fix).

The receiving controller "buying" the handoff means they have looked at the incoming target relative to their traffic and determined that they can allow entry into their airspace. If they need a restriction (altitude, speed, heading, etc) they can call the transferring controller to coordinate that.

The actual transfer of radio communications happens when the transferring controller has determined that, on its planned or assigned heading and altitude, the target will not conflict with any traffic in their own airspace and any entry into a third party's airspace has been coordinated (5–4–5 (c)). This could be tens of miles before the actual airspace boundary depending on traffic, aircraft speed, controller preference or technique, etc—but should be no later than the airspace boundary itself. It will generally be 2-5 minutes before the target actually crosses the boundary.

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  • $\begingroup$ You should edit your answer to specify this is ONLY valid in the United States of America! $\endgroup$
    – pcfreakxx
    Feb 1 at 17:26
  • $\begingroup$ @pcfreakxx, see the very second sentence of the answer... $\endgroup$
    – randomhead
    Feb 1 at 23:24
  • $\begingroup$ Great, thanks for editing! Good night :) $\endgroup$
    – pcfreakxx
    Feb 1 at 23:24
  • $\begingroup$ I didn't edit that, it was like that in my original. $\endgroup$
    – randomhead
    Feb 1 at 23:29

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