47

Here is a list of all the squawk codes (there's 4096 of them). Very few of them have a specific fixed meaning. Probably the only three that always, globally, have the exact same meaning are 7500 (unlawful interference), 7600 (communication failure) and 7700 (emergency). 1200 is used for uncontrolled VFR in the USA. 2000 and 7000 are used for uncontrolled ...


26

To expand upon voretaq7's answer, understanding the history and evolution of transponders can more deeply explain why this is the way it is (for now). When Allied (US/UK/Others) WWII planes returned from combat missions over Germany and mainland Europe, the (brand new technology) radar controllers had no way of knowing "who" the aircraft were. To solve ...


18

The short answer is that they often do both. Mode S transponders (which you'll find on most airliners, and are now becoming common on light aircraft as well) transmit a unique aircraft identifier that the ATC system can interpret and display. Older transponders only support the Mode A identifier code (the squawk code we're familiar with selecting) - this ...


14

Squawk codes are used by air traffic control to identify aircraft on the secondary surveillance radar. Flights are being given a squawk code by an air traffic controller, the pilot dials it into the radar transponder panel, and the radar reads that number out of the transponder and gives it back to the air traffic control system. In the air traffic control ...


7

In addition to the other great answers, you might be wondering why the squawk codes are the way they are — why each digit only goes up to 7 before rolling around to 0. I'm not an aviation expert but I do know about computing so I can answer this question. This is because the transponder is a simple electronic system sending binary information (ie what ...


7

ATC will tell you something like, "N1234R radar service terminated. Squawk VFR. Frequency change approved; good day" which you will repeat back as an instruction. You do not change from the assigned transponder code until instructed. If you're in a hurry to get away from ATC, you may request to terminate radar service as soon as you are out of their, "...


6

7500 hijack 7600 no radio 7700 emergency If you really want to learn, reading the FAR and AIM will really get you up to speed: http://www.faraim.org/ One might wonder why 8 and 9 are not used. I imagine it is to save on bits of data. Numbers 0 to 7 can be done in 3 bits - 000, 001, 010, 011, 100, 101, 110, 111. Numbers 8 and 9 need another bit: 1000, 1001....


4

Currently, FAA's "fusion" software uses discrete squawk codes to merge targets generated by different surveillance systems, i.e. SSR (often several of them) and ADS-B. They plan to upgrade the software so it can merge targets based on Mode S hex code as well, but (as of early 2019) that hasn't been rolled out yet. Once that is in place, ATC will switch to ...


4

Whichever code is assigned to the individual flight by ATC. There isn't a fixed code to use for any one specific route. You might want to see: How does ATC know if you have been assigned a squawk or not?


3

A distress code is not a 'shoot me down' signal. ATC will see the code, and will try to establish contact. If the pilot wasn't with ATC already, they should be on the guard frequency at the very least. For USA, the AIM (Distress and Urgency Procedures) provides the following: If the pilot replies in the affirmative or does not reply, the controller will ...


3

Who would shoot you down and why? You are in the middle of nowhere. Who are you endangering? ATC would try to contact you to ascertain your actual condition. You may have accidentally put in the wrong code. They would then offer assistance if needed. If it was a kidnapping situation, all they could do is follow or track you until you land. You are not ...


3

In addition to those globally recognized special values, and locally valid special values (uncontrolled VR, IFR) you will be assigned the code by the ATC. They will usually assign you a code in sequence from some block they were assigned for this purpose. The exact procedure is highly specific to local procedures. There is some very incomplete (mostly in ...


3

1000 is a blockout code that prevents the ADS-B transmitter from also sending its discrete code, if you enter 1000 on your transponder no Mode 3/A code is sent in the ADS-B OUT message. Its part of AC-20-165B that outlines ADS-B Mode 3/A Code. Currently ATC automation relies on the Mode 3/A code to identify aircraft under radar surveillance and ...


2

Yes. Every aircraft needs to be assigne a discrete code to allow radar systems to correlate flight plan data with the radar target and to enable identification using SSR. The only exemption are aircraft which use Mode S, those can be assigned squawk 1000 and this leads to a correlation of flight plan data using the callsign transmited by the transponder ...


2

There are multiple reasons attributed to the transponders using 4-digit octal codes as the aircraft identifier. Here are two of them which are the most essential: Squawk codes are easier to communicate over radio, and are also easier to read. While there are only 4096 possible combinations, the uniqueness of these combinations are relevant only to those ATC ...


2

Additionally, local air traffic facilities have reserved codes for local IFR and VFR traffic, as well as other codes that may function uniquely in their control environment. As an example, in JAX airspace a local VFR target (one not being handed off to an adjoining facility, will be assigned a 0400 code, local IFR a 0500 code. In ATL, 0100 is the local VFR ...


2

IFR flights outside radar coverage will typically be told to squawk 2000, in contrast with VFR flights that will be squawking 7000 or 1200. Upon reaching radar coverage again, they will be given a new discrete code.


1

If you enter a 7500 code in a transponder, I'd expect the authorities would almost certainly intercept you with instructions as to where to proceed to and land. They have no idea as to your particular situation other than you're transmitting an aircraft hijacking emergency code and they are not going to take chances. As to using deadly force against you, ...


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