If you listen to any ATC recording for departing aircraft, controllers and pilots will refer to squawk codes. These are the transponder codes used to identify an aircraft to ATC. The code can be changed from the specific one assigned to that flight in certain circumstances – most importantly in the event of an emergency when it is switched to 7700.
What is a squawk code?
Squawk codes are used to provide effective communication between air traffic control and aircraft. A squawk code is a four-digit number assigned to each aircraft that aids in identification. This will show up on the controller’s screens, along with vital flight information such as altitude and speed.
Pilots enter the squawk code into the aircraft transponder. This then communicates with ground equipment to display the aircraft information. Usually, an aircraft will keep the same code for the duration of a flight, but it may be changed by other airports or in a particular airspace.
If you are wondering where the term “squawk” comes from, it originates from the Second World War. At that time, basic systems were developed for an aircraft to identify itself to ground controllers – essentially to let them know if the aircraft was friendly or an enemy aircraft. This became known as the “Parrot” system, with the term “squawk” used to refer to the communication between them.
Squawking 7700 in an emergency
Squawk codes are assigned to a flight before departure. The four digits can be between zero and seven – giving 4,096 possible combinations. Reserved codes are used in particular situations when an aircraft wants to communicate something to ATC quickly.
The most well know of these is the code 7700. This is used to indicate an emergency. A pilot will enter this when in an emergency situation – either instructed by ATC after declaring an emergency or without communication. This will clearly inform all tracking ground controllers that the aircraft has an emergency and should be given appropriate assistance.
This could include any emergency or ‘Mayday’ situation such as engine failure, pressurization problems, other technical problems, or medical emergency.
Having such a code available is very useful. It not only advises ground operators clearly of the problem, but it also provides a quick way for pilots to communicate. Every emergency is different, and there may not be much time for discussion. Pilots are trained in an emergency to “Aviate, Navigate, Communicate” – in that order. Making sure the aircraft is flying correctly is the top priority. Of course, communication (including to ATC and internally) is an important but lower priority. Having a fast and clear transponder option can be useful.
Other reserved codes
While 7700 may be the special squawk code we most often hear about, there are others. They serve the same purpose – to provide easy notification to anyone monitoring the aircraft of the situation. These are all (including 7700) defined by The International Civil Aviation Organization (ICAO).
There are two other emergency squawk codes. Code 7500 is used to indicate a hijack, and 7600 to notify that the aircraft has lost communication with ATC. Both of these are, of course, very useful in the situation that radio contact cannot be maintained. ATC will still be able to provide required services and priority. In the event of lost communication, light signal backups can be used.
Codes are not just used for emergencies. There are many other reserved codes assigned by ICAO. These include codes for military operations, search and rescue, and intercept flights. There are also code for specific flights such as glider operations and parachute dropping.
Squawk codes are part of a well-defined universal set of ATC rules. They have been in existence for a long time, with few changes. Feel free to discuss any of these further in the comments.
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