How are squawk numbers assigned?

[kmacka]

I just want to know how squawk numbers are assigned. I know about the different emergency squawk codes and what they mean, but how are all others assigned? Is it a random number that a comp. throws out and they just assign? or are airports/artcc's assigned certain codes to assign to aircraft?

 

[Stavro35]

Just a guess here,and I will ask around. I would assume that the computer assigns the code. It's the only thing that makes sense to me.

 

[Uplink]

I just want to know how squawk numbers are assigned. I know about the different emergency squawk codes and what they mean, but how are all others assigned? Is it a random number that a comp. throws out and they just assign? or are airports/artcc's assigned certain codes to assign to aircraft?

Computer does it. I saw this procedure demonstrated for me by an Air Traffic Controller:

Example: Pilot asks for "flight following"(traffic advisories) to a particular destination. ATC selects the target on the radar, enters aircraft type and destination, computer will respond back with a sqawk code. ATC then relays that code to the pilot. Once the pilot enters the correct code, the code will disappear from the target (verifying the pilot entered the right code), then speed, altitude, destination, and A/C type is shown as the target moves along on the screen.

:wink:

 

[mjw357]

VFR flight following codes, known as a 'local' or 'non-descreet' codes, start with a 0. For IFR flights or VFR flights that have arranged ATC handoffs start with something other than 0, usually 4 or 6.

Not sure how they are generated, but it is not random. If you listen to ATC at a particular location, you will notice that the assigned codes are sequential (0421, 0422, 0423 etc).

 

[Scott_PHX_APP]

My buddy, an Approach Controller here at Phoenix Sky Harbor and others I have talked to about this same question have given me this info. Indeed, the computer assigns the code and as Michael mentioned, the "0"'s are local types, etc. Each ARRTC sector has a block of numbers assigned to it, (Don't ask what goes with what, I don't remember ) and the system assigns the next number in sequence as mentioned, to the requesting controller/ClrDlv/etc. As UPLINK said, the target on the screen is identified via voice etc. and once a code is issued and picked up, the target is "Tagged up". (The part that he mentioned about displaying speed/alt, (mode C, etc) and AC type. BTW, that is at that point, "RADAR Contact". During a departure, the code has been assigned by ClrDelv and the pilot will/should put the code in on the xponder. Once airborne, they switch to "ON" from standby, and as soon as the computer see the code, it "Tags Up" the target automaticly. You hear "Radar Contact" at that point and in cases that the pilot forgets to turn it on, "Check Transponder ON and swk xxxx, etc." Well that was longer that I bet you expected, me too for that matter.
Later...

 

[kmacka]

Thanks everyone, great explanations. Thank you.

 

[crayon]

This is a really good question, but parts of Scott's answers need a bit of clarification. Sorry bro.

Each ARRTC sector has a block of numbers assigned to it ...

This is incorrect. Each ARTCC is allowed to assign a code from 0000 to 7777, with some of the exceptions being:

1200 - VFR
7500 - HiJack
7600 - Radio Failure
7700 - Emergency
7777 - Military Interception Procedures

That being said, there are tiny squawk code ranges that are assigned to each Class C TRACON and/or RAPCON's within an ARTCC airspace boundary for the exclusive use of that facility. Two examples of this would be:

1. A VFR aircraft transitions into Class C airspace. (It is plausible for an aircraft to stay @ 1200, but since an operation in Class C requires communications with ATC, often times ATC will assign a local code to squawk.) Once the aircraft has exited the Class C airspace, it is back to VFR 1200. "Radar service terminated, frequency change approved, squawk 1200, good day."
   
2. A VFR aircraft transitions into Class C airspace, gets assigned a local code to squawk and then requests Flight Following. Upon exiting the Class C airspace the aircraft would be handed over to the Center just as if it were an IFR flight. The local code would be retained unless changed by ATC, the pilot discontinues Flight Following back to VFR, or the flight ends due to it's arrival at the destination.

The exception to this is VFR entry into Class B airspace since it requires a CLEARANCE, (you will get a code ... no and's, if's, or but's here.) and all flights in the DC ADIZ. All other squawk codes issued will be from an ARTCC's pool. The main thing to remember here is that all codes active within an ARTCC's airspace will not be duplicated within that ARTCC's airspace.

With THAT being said, if an aircraft with a code of 1234 crosses a Center boundary where a code of 1234 is already active, a new code will be automatically be generated from the pool and presented to the controller for reassignment.

Once airborne, they switch to "ON" from standby, and ..

Correction, nearly all aircraft checklist's have the transponder to be set to Standby and squawk code set somewhere after engine start. Then somewhere after taking the active, the transponder is set to On or Alt (depending on equipment type), lights on, DG aligned with compass and runway, go with throttle up!

 

[Scott_PHX_APP]

This is a really good question, but parts of Scott's answers need a bit of clarification. Sorry bro.This is incorrect. Each ARTCC is allowed to assign a code from 0000 to 7777, with some of the exceptions being:

1200 - VFR
7500 - HiJack
7600 - Radio Failure
7700 - Emergency
7777 - Military Interception Procedures

That being said, there are tiny squawk code ranges that are assigned to each Class C TRACON and/or RAPCON's within an ARTCC airspace boundary for the exclusive use of that facility. Two examples of this would be:

1. A VFR aircraft transitions into Class C airspace. (It is plausible for an aircraft to stay @ 1200, but since an operation in Class C requires communications with ATC, often times ATC will assign a local code to squawk.) Once the aircraft has exited the Class C airspace, it is back to VFR 1200. "Radar service terminated, frequency change approved, squawk 1200, good day."
   
2. A VFR aircraft transitions into Class C airspace, gets assigned a local code to squawk and then requests Flight Following. Upon exiting the Class C airspace the aircraft would be handed over to the Center just as if it were an IFR flight. The local code would be retained unless changed by ATC, the pilot discontinues Flight Following back to VFR, or the flight ends due to it's arrival at the destination.

The exception to this is VFR entry into Class B airspace since it requires a CLEARANCE, (you will get a code ... no and's, if's, or but's here.) and all flights in the DC ADIZ. All other squawk codes issued will be from an ARTCC's pool. The main thing to remember here is that all codes active within an ARTCC's airspace will not be duplicated within that ARTCC's airspace.

With THAT being said, if an aircraft with a code of 1234 crosses a Center boundary where a code of 1234 is already active, a new code will be automatically be generated from the pool and presented to the controller for reassignment.Correction, nearly all aircraft checklist's have the transponder to be set to Standby and squawk code set somewhere after engine start. Then somewhere after taking the active, the transponder is set to On or Alt (depending on equipment type), lights on, DG aligned with compass and runway, go with throttle up!

No problem on the correction. Indeed my buddy mentioned the assignments were not per ARTCC, but as you said, any number as you listed. What I was thinking was that each TRACON uses a base number group, like 4xxx or 2xxx, etc. I believe they use the 0xxx here for local area flights and such. The main thing is the computer doesn't issue the same numbers twice. Also, local flights such as Care flights or TV choppers can/will have a pre-assigned code to them so the tower/TRACON knows who they are from the start. They still have to ID them, but it's just a bit faster. My bad on the use of ARTCC part. As far as the check list goes, that's for sure, but I guess things get busy in the cockpit now and then since you hear that dreaded "Check Transponder ON" thing now and then. Anyway, I got some of it right... :lol:
Later...

 

[K4DHR]

With THAT being said, if an aircraft with a code of 1234 crosses a Center boundary where a code of 1234 is already active, a new code will be automatically be generated from the pool and presented to the controller for reassignment.Correction, nearly all aircraft checklist's have the transponder to be set to Standby and squawk code set somewhere after engine start. Then somewhere after taking the active, the transponder is set to On or Alt (depending on equipment type), lights on, DG aligned with compass and runway, go with throttle up!

That is correct. I generally would set the transponder to ALT as part of my run-up routine. At an uncontrolled airport on an IFR flight plan you generally wouldn't have a squawk code until given to one by clearance delivery, which usually occurred after doing a run-up.

I haven't been behind the controls of an airplane in the air in about 4 years now, so I'm a little rusty on some things. I wish I had the spare income to be able to fly again!

 

[b7spectra]

Wow! I forgot about 7770. When I flew as a flight medic back in the 80's, I would always see that on the display when we were transversing ATL! We always got permission to overfly the field when on an emergency call. Now, when if we got canceled, we had to take the long way around on the return flight!

 

[crayon]

At an uncontrolled airport on an IFR flight plan you generally wouldn't have a squawk code until given to one by clearance delivery, ...

Actually ~30 minutes prior to P-Time the FAA's computers have generated a code .. only you don't know about it yet!

As mentioned, anything can happen at uncontrolled airports. You may have to be airborne just to establish radio contact with ATC.

 

[K4DHR]

Wow! I forgot about 7770. When I flew as a flight medic back in the 80's, I would always see that on the display when we were transversing ATL! We always got permission to overfly the field when on an emergency call. Now, when if we got canceled, we had to take the long way around on the return flight!

Interesting. Usually I'd just ask the controller to overfly the field to go over downtown, usually when I was carrying friends to show them around. There *was* a ATC VFR "route" you could request over the field, controller workload permitting. I think I was only denied this once. I was flying out of KFFC and KCCO at the time.

 

[N1508J]

Uncontrolled airport????

That is correct. I generally would set the transponder to ALT as part of my run-up routine. At an uncontrolled airport on an IFR flight plan you generally wouldn't have a squawk code until given to one by clearance delivery, which usually occurred after doing a run-up.

I haven't been behind the controls of an airplane in the air in about 4 years now, so I'm a little rusty on some things. I wish I had the spare income to be able to fly again!

Now now, be nice and call such airports non-towered.

Being in the DC ADIZ we have to get the squawk via land line from Potomac Approach before cranking the prop!

 

[b7spectra]

Interesting. Usually I'd just ask the controller to overfly the field to go over downtown, usually when I was carrying friends to show them around. There *was* a ATC VFR "route" you could request over the field, controller workload permitting. I think I was only denied this once. I was flying out of KFFC and KCCO at the time.

When I worked as a traffic reporter in the 90's, the pilot would call the tower & get us clearance to cross. Usually, on the way back, we had to take the long way around. It was always nice as a flight medic for the pilot to just say "LifeBird 1 flight on emergency transport" and ping the transponder!

I still get to go up in 2AQ every so often - helps when you used to do traffic with good old Captain Herb!

 

[cpuerror]

Is there some way of picking up squawk codes at home? ie scanner connected to the soundcard ??

 

[crayon]

Is there some way of picking up squawk codes at home? ie scanner connected to the soundcard ??

http://www.javiation.co.uk/sbs-1.html

 

[b7spectra]

I think I can find a better use for 389.95UK/794.99US!

 

[sopdan]

So if I'm on an IFR plan, why does Center so often change my squawk during the flight? (I have ideas, but it'd be nice to know the exact reason) This has happened quite a bit in the last two weeks, on flights that remain w/in one or two ARTCCs.

Just curious.

 

[cpuerror]

I think I can find a better use for 389.95UK/794.99US!

I agree. I think i'm just going to have to manage to make it without been able to read squawk numbers.

 

[crayon]

I have ideas, but it'd be nice to know the exact reason

If you can tell me what your thinking, I can ask and find out.