Transponder code

Transponder codes are four digit numbers broadcast by the transponder in an aircraft to assist air traffic controllers in traffic separation. A transponder code (often called a squawk code) is assigned by air traffic controllers for IFR or a VFR flight following. Most squawk codes are simply numbers assigned by ATC but there are some that have their own meaning and are used when radio communication is impractical or impossible.

1200: VFR flight, this is the standard squawk code used when no other has been assigned.

Emergency codes:

7700: basic in flight emergency code. will cause alarms to go off at all stations that pick it up and grant immediate attention from air traffic controllers monitoring the area.

7600: radio out. This code lets controllers know that the plane squawking it is having radio problems but other electrical systems are working.

7500: highjack code. a plane squawking this code will be given any assistance requested.

0000: military escort.