Squawking and VFR/IFR codes

A

AmericanJetBlue

New Member
I once was monitoring JFK tower via liveatc.net and i once heard Clearance Delivery/Ground Control tell the aircraft(in this case a JetBlue A320) not only his taxiway clearance, but things like, expect takeoff 13R, fly runway heading, climb and maintain 5,000, vectors greke, j26, white, expect flight level of 320 after 10 minutes from departure, squawk 1551. I understand pretty much most of that except the squaking part. Explain please? Thank you
 
A squawk is essentially slang for putting a unique 4 digit code into the transponder.

The transponder is what sends back the data tag to ATC. On your data tag are things like your callsign, airspeed, altitude, type of aircraft, and other miscellaneous data (such as, if your tower, the runway approach assigned).

For a complete understanding of how all this works you have to understand basic radar. In a nutshell, the radar (that spinning red thing you see at airports) sends up a signal. This is known as the interrogator and this "interrogates" the transponder. It essentially asks it "are you 4063?" The transponder will reply "I am 4063 and here's my information" it does this for each sweep of the radar.

Now, if the transponder is switched off all the ATC may see is primary blip, which appears nothing more than a "/". A primary blip is just the radar signal bouncing off your metal fusalege back to the ground. Or it may show a target without a data tag.

I'm sure I've probably screwed something up with my oversimplification here and I hope someone will correct me.
 
PurduePilot said:
I'm sure I've probably screwed something up with my oversimplification here and I hope someone will correct me.
Click to expand...

You got it mostly right, except that the transponder does not send out any information other than the squawk code and altitude (if Mode C equipped). All the other information (aircraft type, flight plane, etc), are in ATC's computer, and whenever your transponder replies with it's code, the computer takes that and puts it together with the information in it. To put it in terms of your dialog, basically radar says, "Who are you?" the transponder replies, "I am 4063," and ATC's computer then says to the controller, "This is 4063, and according to my records 4063 is a ......" You get the idea.
 
OK, something more deep than that. . .are the squawk codes preassigned to regions or ATC areas? Next question is related to the first. . .why do you sometimes have to change squawks during flight?
 
Each facility has a block of codes assigned for their use to prevent duplication. You have to change codes from time to time to prevent one facility "stealing" another's code for the duration of the flight. If you didn't change codes, the facility that assigned you that code would be less one code for an aircraft no longer in their airspace.
 
Sorry, but your comment isn't exactly clear to me. Stealing a code? Is there something systemic to the ATC system that identifies that possibility? I'm still not exactly clear what example/situation would occur for that to happen.
 
Well let me try to put it another way. There are only so many usable codes and only one central database. Lets say you allow controllers to assign codes as the first 4 numbers off the top of their heads. Lets imagine AAL 129 is assigned to squwak 4280 (the controller just turned 42 and his favorite team just scored 80 points that day so the number is fresh in their mind) for a flight from BNA to LAX. 20 minutes later a King Air (call it N12345) is assigned the same code (they just totalled their car to the tune of $4,280 and so that number is the only one they can think of) from another controller for a flight from some midwestern strip to MCI. The central database isn't going to know if it should display the flight plan and aircraft data for AAL 120 or N12345 for either aircraft on a controller's scope. Because of that, controllers cannot assign squawks at their discretion. Memphis center is going to wonder how a King Air is tooling along at 420 knots, likewise ZKC is going to wonder why an LAX bound ALL 737 is heading east at 240 knots.

The only solution is give facilities codes to use for flights starting in their airspace. There are still only so many codes and they need to further break them up. Lets say we let codes be used for the duration of a flight. You could possibly get a situation where higher than usual departures from one facility result in a situation where that facility has no more codes left that aren't in use because all the aircraft with the codes assigned to that facility are still airborne. That was what I meant by "stealing" a code. If the plane is still airborne and locked into a code, it can't be used again until that plane lands.

Hope that clarifies. The system isn't smart enough to track aircraft squwaking 4280 westbound and know it is AAL 129 as opposed to eastbound N12345.
 
first point you cannot have a 8 or 9 in a beacon code only 0 to 7.

as for codes all centers have there own subsets for internal and external use and they are given so centers next to each other dont have the same code subset this is to cut down the number of code changes.ive spent 20 years at ZAU and ive never heard of a central beacon code data base, thats because there isnt one.each center computer trackes its own beacon codes an aircraft in NY and a aircraft in LAX with the same beacon code are in two diffrent centers computers and each computer will be able to track there own aircraft. if 2 aircraft enter the same centers airspace with the same code the NAS computer for that center will assigne the second aircraft a diffrent code.an aircraft flying from JFK to LAX can have the same beacon code for the whole flight as long as there isnt an aircraft with the same code in that centers airspace as they fly form center airspace to center airspace.i dont know were you get you info but beacon codes are not lock for a flight and are changed when a center computer has more then one aircraft with the same code.you can have 22 aircraft in the 22 centers airspace all on the same code and it will work as long as any one aircraft dose not enter another centers airspace, if it dose the computer just assignes a diffrent code. as for how code are assigned the computer assignes them randomly not the controller.once an aircraft leave a centers airspace and after 10 minutes of a hand off to another center the beacon code can be assigned to another aircraft.and yes the system is smart enought to know who is who.
 
Sorry about the two above posts on my account which are very wrong. Neither post was by me and I generally do not post here. A couple of friends who live next door and have just started the CTI program here have been having internet issues recently and I've been letting them use my computer so they can check their email and such. Whichever one of them it was meant well, but obviously doesn't know enough yet (squwaking with an 8 in the code? seriously) I believe I've learned my lesson about auto login.

If I can figure out how to delete them I will.
 
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