Why are squawk codes changed in flight?

[Dragonmount 5]

I've been using RC4 for years and I've noticed that sometimes on a flight you can be asked to change your squak several times in a flight, and I was curious about why this was? Forgive me if I misspelled the word, I've never actually seen it written.

[Cjr60611 31]

That's a good question.  I have wondered the same; do real life pilots have to change codes during flight?  If so, it makes sense as the ATC system seems to be an intricate puzzle of radio centers and pathways with each center dealing with it's own traffic patterns and efficiencies.  It would seem logical that ATC centers would assign squawk codes to aircraft as they enter controlled space so they can manage their existence (movements).  Very much like a parking garage valet tickets a car when it enters; it may be a lime green Mustang with Alaska plates and all.  Still, the valet has his own system on how to manage, store and recognize it's your car so it and you get a unique ticket with a number assigned to it. 

 

Real world pilots or controllers?

[Sticky 267]

In the USA, I believe that squawk codes are created by the initial ARTCC that hosted the flight.  As the aircraft progress along it's route, sometimes it will enter a neighboring ARTCC which has already assigned that code to a different aircraft.  The ATC computers discover the conflict and issue the new aircraft a new squawk.

 

Sound about right, ATCers?

[Dragonmount 5]

I figured it was something like that, I remember hearing around the time of 9/11 that that was one of the big things among the conspiracy nuts, that the squawk code was changed during one of the flights. I knew back them that it was common to change but I had no idea why.  Thanks!

[michal 44]

I've been using RC4 for years and I've noticed that sometimes on a flight you can be asked to change your squak several times in a flight, and I was curious about why this was? 

Because it is RC4, simulation and not reality. In reality having to check squawk code is very rare, doesn't happen in the US very often. I have been flying IFR in small aircraft for years and never had to change original squawk code. Also frequency changes are also too frequent in RC4.

[bonchie 2,305]

Personally, I've never had them make me change it in real life. They always let me keep it from when I initially pick up the clearance to landing. Even entering the DC SFRA, they use the same code.

[dmwalker 601]

I have noticed that the squawk code changes on transatlantic flights. For example today's Lufthansa flight DLH470 had the squawk code 0626 over Europe, then 6347 over Canada. Are transatlantic flights a special case?

[KevinAu 441]

Aircraft in non radar oceanic airspace squawk 'oceanic' ie. 2000 when they fly off the scope. Similar to squawking 'vfr' 1200. When reentering radar airspace, they will be given a discrete squawk code.

 

Squawk codes can change during the course of a flight. Not all the time, but not uncommon either.

[t_a_h 0]

But still, the reason for why they get changed isn't clear to me.

[scottb613 1,187]

Hi Folks,

 

RW - VFR aircraft on Flight Following change all the time - at least here in the NE USA... I believe it's related to how the originating controller builds you into the system... They have codes for local ops and others for handoffs... Maybe it's quicker to just build a local one if time is short ??? I've been asked to change plenty of times - the longer flights crossing ATC Center boundaries seem to have a higher incidence of changing...

 

Regards,

Scott

[MartinRex007 390]

Also in real life you might be ask to change your squawk code say from VFR 1200 to something else so ATC can make a positive identification of you. I've had that happen a number of times.

 

Cheers

Martin

[BrianW 124]

One thing that can cause a squawk code change is a late departure. If your flight plan expires between the time you picked up your clearance and your takeoff ATC usually needs to scramble to get your plan back in the system. This can cause a code change, but you will usually get the new code either right before departure or shortly after.

[skelsey 765]

As mentioned above, there are numerous reasons why a squawk might be changed in flight.

 

VFR flights may be allocated a discrete squawk by the ATC unit working them, both for their local identification purposes and also to indicate to other units that the flight is being worked by a particular unit -- so if, for instance, the area controller above wants to co-ordinate they can quickly see that a particular aeroplane is being worked by, say, Borton Radar.

 

The nature of VFR (i.e. usually outside controlled airspace) is that generally speaking the flight will not be handed over from one ATSU to another, but in effect "released" to the open FIR (and thus will be instructed to squawk the local VFR code) until they freecall the next unit -- who may issue their own local code for the same reasons indicated above, until they are no longer working the traffic when again they will usually instruct them to squawk the local VFR code and change frequency at their discretion.

 

IFR squawk changes will depend more on the "interconnectedness" of the ATC centres a flight is passing through. So in the Eurocontrol area, for instance, which is fairly well-connected in terms of computer systems, a squawk would be likely to remain throughout the flight (and I would imagine the same situation for the USA). However, there are some situations where the code may change -- for example, there are areas in Europe where Mode S identification is used (which does not rely on the Mode A code) and therefore suitably-equipped aircraft will be instructed to squawk 1000 to release the mode A code when transiting these areas -- on contact with a new unit which requires a discrete Mode A code for correlation, a new code will be issued.

 

As mentioned above, when leaving radar airspace (i.e. in Oceanic airspace) the procedure is to squawk 2000 so that a suitable code can be issued when re-entering radar coverage -- again, code allocation will not be co-ordinated between Europe and the USA, for instance (apart from anything else -- there wouldn't be enough codes!) so a code would need to be issued in the US system for westbound flights or in the Eurocontrol system for eastbound flights. Likewise, when transiting between countries with ATC systems that are not connected to each other (for either technical or political reasons) you could easily get a new squawk at each FIR boundary.

[HighBypass 2,339]

There's an emergency squawk code too isn't there?

[scott967 62]

I wonder if things change with mandatory ADS-B coming online?

 

scott s.

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