Transponder codes: Any rhyme or reason?

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
I've been noticing a bit of a pattern when being issued a transponder code for local and cross country Flight Following or IFR flight.

When doing close in practice work around the home aerodrome, I am frequently issued a code that begins with a zero and sometimes a two.

On cross country activities, it starts with a five and ranges from five-two to five-six.


1. Has anyone else noticed similar patterns for their flying?

2. Is there any "if you're doing this, you're gonna get that" sort of logic to transponder codes?
 
The controllers will be along soon enough, but yes, there are "local codes" that get handed out when you're just going to maneuver in the area, for arrival at some Delta airports, and for short hop Flight Following like DTO to FTW.

There was a thread recently about the 'number of codes' based on math that also referred to some of the carve outs. It also explained why you sometimes check on to a new frequency and get assigned a new code.
 
I get the same here.

From my understanding, the 02-- codes are local codes for VFR flights that stay within the local airspace. The Center has a bank of codes for flights that also just remain in their airspace. Different sets of codes for different airspace is organized in a way to minimize the need to change the beacon code's while in the air and also to avoid overlap with other nearby facilities.

If you are issued a 5--- code, ATC is putting you "in the system." Ex. A VFR cross country flight that will fly through multiple sectors of airspace.

IFR codes are dispensed in a similar manner, although they are not always limited to a certain series of numbers.
 
Sometimes the radar facility has to change your code. Lets say I call up a tracon for local flight following, they may asign one of the local codes (02xx or 04xx seems to be the most common). If I then tell them that I want to go to a spot just outside of their space, they may come back with a change in transponder code to a 5xxx or 4xxx. As it was explained to me, the controller has all the local codes already available on his console and he can just tag up a plane with those available codes. If he needs one that can cross boundaries with center, he has to punch the rudimentary flight plan into the 'national airspace computer' and it spits out an assigned code for that destination. Just one extra step in the process.
 
I've noticed a difference in the codes I get for my personal plane and the work plane too.

Lots of 53XX codes.
 
There are also subsets of codes exclusively for VFR that are non NAS codes (ie can't hand off automatically to adjacent sectors) that process MSAW data (terrain and traffic alerts) which are to be used only at pilot request or in the case of a mayday call-up and the appropriate 7xxx code is impractical.
 
I had my first 7746 squawk code from ZLA a few months ago. My wife likes to help with the transponder... I had to slap her hand on that one.


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Tampico Trauma said:
I had my first 7746 squawk code from ZLA a few months ago. My wife likes to help with the transponder... I had to slap her hand on that one.


Sent from my iPhone using Tapatalk
Click to expand...

I don't even go to standby on those. If ATC sees a 7700 flash for a split second, they won't care. Saw several false alarms when I worked ATC.
 
Velocity173 said:
I don't even go to standby on those. If ATC sees a 7700 flash for a split second, they won't care. Saw several false alarms when I worked ATC.
Click to expand...

"What's wrong?"

"If that thing says 7700, we're going to be asked to copy a phone number."

"But they said 7746"

"Start from the right"


Sent from my iPhone using Tapatalk
 
IMG_2284.JPG
Tampico Trauma said:
"What's wrong?"

"If that thing says 7700, we're going to be asked to copy a phone number."

"But they said 7746"

"Start from the right"


Sent from my iPhone using Tapatalk
Click to expand...

Oh, I doubt you'd even get a number. It's not a pilot deviation. I've had a student select emergency on our APX-100 before. He rotated right past "normal" to "emergency." ATC queried but that was all. Looks just like this transponder...old school.
 
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AggieMike88 said:
I've been noticing a bit of a pattern when being issued a transponder code for local and cross country Flight Following or IFR flight.
Click to expand...

I'm not in the system often. The one class C I fly into has a block of numbers and assigns them sequentially.

Many years ago I flew in an area where a facility had a block of numbers, but would usually incorporate a part of your tail number into the code. I suppose that was before the computers would tag a target. Not sure which facility assigned, the codes. It may have been military.
 
Tampico Trauma said:
"What's wrong?"

"If that thing says 7700, we're going to be asked to copy a phone number."

"But they said 7746"

"Start from the right"


Sent from my iPhone using Tapatalk
Click to expand...

That's silly. Dial the code and get on with it. ATC isn't stupid, they know you might pause on 7700 for a moment.
 
Plug in the code given,and don't worry where the number comes from.
 
AggieMike88 said:
I've been noticing a bit of a pattern when being issued a transponder code for local and cross country Flight Following or IFR flight.

When doing close in practice work around the home aerodrome, I am frequently issued a code that begins with a zero and sometimes a two.

On cross country activities, it starts with a five and ranges from five-two to five-six.

1. Has anyone else noticed similar patterns for their flying?

2. Is there any "if you're doing this, you're gonna get that" sort of logic to transponder codes?
Click to expand...
Great question. Few people care about this, but I always found it interesting. There are a few problems with getting a local code in that they usually do not permit inter-facility handoffs, especially when the radar systems at two facilities are different.

There are a few subsets:
1. VFR being worked by a control tower - local (Regional Approach's database)
2. VFR flight following - local.
3. VFR practice approaches or IFR - local.
4. VFR flight following or IFR, terminating inside ZFW - center database. (aka "Internal")
5. VFR flight following or IFR, terminating outside ZFW - center database. (aka "External")

Subsets 1 and 2 above inhibit minimum safe altitude warnings. Subsets 3-5 will result in minimum safe altitude warnings if the system detects you descending too fast or operating below the MVA.

All of the codes issued by our local control towers (except for IFR clearances) are tied into the Regional Approach database. Regional Approach is delegated the following subsets by the National Beacon Code Allocation Plan: 0100, 0200, 0400, 4300, and 4600. You'll notice the control towers will issue 04XX codes if they want to "tag up" VFR inbound aircraft on their radar display. A couple controllers at Dallas Executive and other area towers do this regularly. If you call up Regional Approach for flight following and are not conducting practice approaches, they'll usually issue a 46XX code. Practice approaches around here usually get a 52XX code.

If your route will take you from ZFW to another center's airspace, you'll be assigned a 0500, 0613-0677, 2200, 2300, 3021-3077, 3241-3264, 3400, 3600, 6200, or 7041-7077 code.

If your whole route will remain within ZFW, you'll get an internal code in the range of 4500, 5100, 5200, or 5300.

If Regional Approach changes you from a 46XX code to a 53XX code, that means they just "put you in the NAS," and you can expect flight following all the way to your destination.

All of this is contained in NBCAP documentation, available publicly online.
 
Cooter said:
That looks familiar!!
Click to expand...

Yeah, a museum piece...literally. :D Ours looked just like it, only mode 2 could be manually dialed in. Not that you'd need to in flight though.
 
Tampico Trauma said:
"What's wrong?"

"If that thing says 7700, we're going to be asked to copy a phone number."

"But they said 7746"

"Start from the right"
Click to expand...

I would guess that on a GTX330, you have to enter from the left but nothing happens until the full code is in - unlike the older 4 physical dials.
 
geneseib said:
I'm not in the system often. The one class C I fly into has a block of numbers and assigns them sequentially.

Many years ago I flew in an area where a facility had a block of numbers, but would usually incorporate a part of your tail number into the code. I suppose that was before the computers would tag a target. Not sure which facility assigned, the codes. It may have been military.
Click to expand...
That would have been an early version of a system called TPX42. It didnt do data processing and didnt put the aircraft call sign on the scope. It did display the 4 digit numeric code on the scope. A facility would have a block of codes assigned like 0400-0477. They could get as creative as they wanted with the last 2 digits as memory joggers. The Navy used it a lot back then, don't know about the Air Force.
 
In short, yes, there is a pattern to code assignments. There are nationally mandated non-discrete codes (xx00) that are based on certain kinds of operations. There are a few discrete subsets (a range of discrete codes) that are nationally reserved.

In general each approach facility will be assigned a subset of discrete codes with which they will utilize at their discretion based on the local operating procedures. For example, VFR practice approached may use codes from one subset while VFR inbounds or outbounds my use another. Each facility fashions their usage to best meet their needs. That includes, possibly, changing the code during the flight to reflect a change in the type of operation, ie., a change from VFR practice approach to IFR practice approach.

A lot of the recent (last 10 years) code procedures are also associated with the way facilities count traffic. A software program called Count-Ops automatically counts traffic based on a set of rules set up in the program and many of those rules depend on code subsets. These counting rules can use the code subset, data block scratch-pad entry, and data block special designator in their design. By having aircraft squawk different codes based on their operation and location the computer can keep track of traffic count with at least a 98% accuracy.

Just as an example, an aircraft going to a satellite airport will be counted as at least a VFR count. It might also include multipliers to that count value based on if it goes to a satellite airport in a Class B or outside a Class B. Or any other rule established in the counting program. These rules follow strict national guidelines. This "counting" established the levels of each facility.

So there are many reasons for the assignments of local codes, some procedural and some designed to facility traffic count. All of them locally designed, either local to approach facilities or enroute facilities.

In addition, going enroute from one center to another, or better stated, one ERAM host computer to another, will generally require a new enroute code assigned by the receiving ERAM host computer.

tex
 
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I got 1011 coming out of DAB headed home to EQY a couple of weeks ago...VFR flight following. Binary code???
 
I was very amused one time to get 5327 as my squawk (the same as my N number).
 
AggieMike88 said:
I wonder if the issuing controller saw that too...
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Yeah, there was a little chuckle when he issued it, so I think he knew it matched (either a great coincidence or he pulled it out of the pool specifically).
 
arnoha said:
Oh, that's a great link!

Found this gem:

4400 - SR-71, F-12, U-2, B-57
Click to expand...
Interesting. All those aircraft were capable of entering/exiting the NAS from above.
 
Tampico Trauma said:
"What's wrong?"
"If that thing says 7700, we're going to be asked to copy a phone number."
"But they said 7746"
"Start from the right"
Click to expand...

Could be worse, she could have entered 7777 (used around here on the border when you're intercepted and getting formation experience with a F-15:confused:).
 
When requesting FF for example out of PHX. and flying to TUS. tell them you want FF "with a center handoff" you will get a center squawk. makes things easier for the controller. otherwise they might dump you and you have to call up center as a cold call. or you will waste the controllers time by them asking if you want FF the whole way and assign you another code.
 
I had 7074 recently with DFW Bravo, Dallas departure, Waco, and Houston Approach. VFR FF.
 
There are some special ones that aren't well known. '3333', for example, is used for flying over a large forest. Tomorrow you might get '1776'. And if a pilot squawks '0000' it means "Do not disturb -- Mile High Club initiation in progress."

:D:D
 
skippy101 said:
When requesting FF for example out of PHX. and flying to TUS. tell them you want FF "with a center handoff" you will get a center squawk. makes things easier for the controller. otherwise they might dump you and you have to call up center as a cold call. or you will waste the controllers time by them asking if you want FF the whole way and assign you another code.
Click to expand...

On that flight, you don't have to tell them you want a "center handoff" as you go from PHX approach, ABQ Center and TUS approach anyway if you request flight following. I just wish the Class Ds could give a code other than 1200. I've had to cold call PHX approach every time to get flight following to TUS.
 
Timbeck2 said:
On that flight, you don't have to tell them you want a "center handoff" as you go from PHX approach, ABQ Center and TUS approach anyway if you request flight following. I just wish the Class Ds could give a code other than 1200. I've had to cold call PHX approach every time to get flight following to TUS.
Click to expand...


Yep coming out of SDL. you need to contact PHX TRACON quickly before entering class B. Would be nice if SDL TWR would set you up on Clearance del freq.
 
Heard late one night on center frequency.

airplane: Center Medivac 12345 9500 IFR to ABQ.

Center: Medivac 12345 cleared to ABQ as filed, climb 17,000 squawk 0808.

airplane: I don't seem to have any 8s on my transponder.

Center: (different voice) Ok, if you have any threes try 0303.

Different aircraft (not me, honest) Go fish...
 
AggieMike88 said:
I've been noticing a bit of a pattern when being issued a transponder code for local and cross country Flight Following or IFR flight.

When doing close in practice work around the home aerodrome, I am frequently issued a code that begins with a zero and sometimes a two.

On cross country activities, it starts with a five and ranges from five-two to five-six.


1. Has anyone else noticed similar patterns for their flying?

2. Is there any "if you're doing this, you're gonna get that" sort of logic to transponder codes?
Click to expand...

Transponder codes are assigned in accordance with Order JO 7110.66E National Beacon Code Allocation Plan.
https://www.faa.gov/documentLibrary/media/Order/JO_7110.66D_.pdf
The 0100, 0200, 0300, and 0400 code blocks are allocated to terminal facilities for their internal use. These are assigned to aircraft that have not been entered into the overlying ARTCC's Flight Data Processing Computer.

Aircraft filed IFR are assigned codes by the originating ARTCC's computer. These codes come in two flavors; internal and external. An internal code is assigned when the flight will take place solely within the originating center's airspace, including airspace delegated to approach control facilities. This allows ARTCCs that do not share any radar sites to use the same internal code blocks. External codes are assigned to flights that will exit the originating center.

ZFW uses the 0500, 2200, and 2300 code blocks for external departures.
 
Interesting about the codes and how they're used. That explains a couple things. Just today I flew down to Aircraft Spruce to pick up a few items, and decided to get FF, in the hope that I would be allowed to transit the ATL class B. On initial call up, I was given a code to squawk. A 32 something.
When I got the "radar contact, atl alt 2996" It was followed by "squawk 0123, cleared through bravo". I was still about 15 miles out of bravo.
On the return trip was given the code 73 something. And kept that code untill I canceled FF, and started my descent to JZP.
I had never been given a code beginning with a zero until today.
 
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