Quick transponder question

[scotchegg 4,271]

In all of the sims I’ve used, when flying into a new ATC area with flight following, they automatically seem to know what my transponder code is (or at least they never assign a new one).

Is this real? Does one ATC zone contact the next when they pass you over and give them the code or something?

Edited January 28, 2023 by scotchegg

[qqwertz 807]

I can only judge from Vatsim, but they aspire to be as real as they can be. On Vatsim, you usually do not get a new transponder code when you are handed off, the information is transferred. However, it also happens fairly regularly that ATC assigns a new code to you. 

Peter

[rka 916]

I may be misunderstanding the question, but your transponder is actively sending the code, that's how they know. And when they transfer you from one controller to the next, they just pass it on.

[scotchegg 4,271]

14 hours ago, rka said:

when they transfer you from one controller to the next, they just pass it on.

That's what I guessed, but I was just interested in how that happens practically. Is there a shared IT infrastructure between all national / regional ATC, or are they literally calling the next ATC area up and giving them the code verbally...?

[C2615 322]

Upon first contact you should tell ATC your squawk number anyway.

On mode S transponder it would also send information like your call sign and tail number, so ATC can directly identify you on their radar.

But it's not impossible you have same transponder code as others when you fly into new areal, as there is only less than 4096 to spare, in that case you'll got a new one without conflict.

Edited January 29, 2023 by C2615

[jon b 2,078]

The air traffic systems are linked to a central computer system which has information stored about flight plans and the squawk issued , at least that’s what used to happen in the uk. 
Up until the end of the 1980s the U.K. system was run on an ageing IBM 9020 computer which they bought from the Americans.The same computer was also used by the FAA and I recently saw one in the national air / space museum at KIAD.

I presume the same system is used nowadays but just with much more powerful hardware.

Also  regional airports that provide radar services in the uk have their own Codes defined by the first 2 digits, for example local traffic receiving a radar service from Manchester radar EGCC will be issued a code beginning with 73 ranging from 7350 to 7365.

Neighbouring radar units can then see which ATC unit is working a particular radar target by seeing what code it’s wearing.

Also specific operations such as a SAR helicopter mission will have its own specific code that it usually wears , similar police, met observation flights etc all have their own codes discreet codes that controllers can see and know what that aircraft is up to even though it’s not in their airspace or talking to them.

For example a military aircraft climbing out from low level will wear the code 7001 , that way when a radar target suddenly pops up from seemingly nowhere the controllers will know instantly from this conspicuity code what it is and what it’s up to.