Flightradar24 Blog

What are squawk codes used for?

Share this article
  • A look at what squawk codes are
  • How squawk codes work
  • Examples of famous squawk codes

You may have heard of the infamous code 7500 which airliners transmit when they are being hijacked, common amongst movies and TV shows, but what do squawk codes like this actually mean and why are they used? Here, we’ll look at their history and some common squawk codes which have become well-known within the aviation community.

What are Squawk codes?

Squawk codes are what air traffic control (ATC) use to identify aircraft when they are flying. They are unique four-digit numbers and range from 0000 to 7777; some of which are fixed values signifying specific scenarios (see below), others being randomly generated by ATC. At the dawn of commercial aviation, the position of an aircraft was tracked using radar, and aircraft would show up as anonymous dots on ATC radar display. However, as air travel became more popular and the skies more crowded, this method became ineffective and even dangerous since there were too many planes and a means of distinguishing one plane from the next was needed.

This is where squawk codes came in. There are 4096 unique combinations aircraft can use to identify themselves. When the aircraft enters an ATC’s airspace, the ATC generates a squawk code for the aircraft, and radios the pilot to enter it into their aircraft’s transponder. The aircraft transponder then continually transmits this back to the ATC, and the squawk code will be displayed next to the aircraft’s dot on the tracking screen.

The pilots are designated a Squawk code by ATC, before they enter the code into the transponder.

Famous Squawk codes

As well as the codes used to identify aircraft, there are three squawk codes which aren’t randomly generated and are used to communicate to ATC without the use of speech. They tend to be used in emergencies, and work by the pilots changing their squawk code away from their designated one, signaling to ATC what is happening on board. These special codes are standardized by the International Civil Aviation Organization (ICAO), so seeing an emergency code in Denver means the same thing as seeing the code in Delhi.

The first of these is the code 7500, which signals “unlawful interference,” more commonly referred to as hijacking. This is a situation where squawking is particularly useful, as it allows the pilots to contact ATC discreetly. What happens after this code is transmitted varies, but usually,  security forces tend to get involved. The process which is depicted in movies and TV is an escort by military aircraft, but other things happen such as authorities waiting upon arrival. 

Squawking 7500 signifies an aircraft being hijacked and could result in an aircraft being escorted by military forces.

Can’t talk now, sorry

The second emergency squawk code is 7600, showing ATC that the aircraft has lost verbal communication. This could mean that it can still hear ATC and yet not respond, in which case the ATC will direct the pilot to speak with them through the Ident button. This is a small button on the transponder which causes the aircraft to flash on the controller’s screen and therefore can be used as a means of talking through non-verbal communication. Interestingly, if the pilot can’t hear ATC or speak to them when near the airport, they can often communicate with the aircraft through lights. These come from a light gun situated on the tower, where ATC shines lights at an aircraft in colors of either red, green or white to signify different things when the aircraft has lost communication. These light gun signals mean different things depending on whether the aircraft is on the ground or in the air, and their values are taught to pilots during training. 

Generally speaking

And finally, the last emergency code that can be squawked is 7700, which can be used for general emergency. An aircraft may even be directly asked to squawk 7700 after speaking to ATC verbally so that they can recognise them and give them priority over others. Squawking 7700 gives the pilot the responsibility to do essentially anything to ensure the safety of those onboard, regardless of the rules. Squawking 7700 also notifies all nearby ATC in the surrounding areas of the situation with the flight. 

Squawk codes are a key part of managing flights everywhere, and without them, the skies would be a lot more chaotic and unorganized. So, the next time you are on Flightradar24 and looking at an aircraft’s details, check the squawk code to find out what’s going on onboard. It’s most likely that it will just be a random number, but, in rare cases, there could actually be something significant happening.

On The Radar Logo

Get the latest aviation news delivered to you

Get the latest aviation news delivered to you

Flight tracking and aviation industry news direct to your inbox

Aviation news comes quickly, so join more than 600,000 others who receive weekly aviation industry and flight tracking news from Flightradar24 direct to their inbox.

Share this article

Useful flight tracking glossary

View our glossary of terms which you may encounter either on our site or in aviation in general that we hope enriches your flight tracking experience.

About Flightradar24

Flightradar24 is a global flight tracking service that provides you with real-time information about thousands of aircraft around the world.

Don't miss out on the latest Flightradar24 videos!

Subscribe to our YouTube channel to see our latest videos as soon as they’re published!

Latest video
On The Radar Logo
Get weekly updates on Flightradar24 and have the latest aviation news land in your inbox.

How flight tracking works

Flightradar24 combines data from several data sources including ADS-B, MLAT and radar data.
Search the blog
Trending articles
Follow us
Latest AvTalk Podcasts
Related news

Flight tracking top 10 aircraft

Explore the top 10 most tracked aircraft and find out why these particular aircraft draw so much interest.

Help to grow our flight tracking coverage

We are continually looking to improve our flight tracking and the airports below are where new receivers will add the most coverage. Apply for a receiver today and if accepted you’ll receiver a free Flightradar24 Business Subscription.

Free ADS-B Receiver
Flightradar24 logo
Try the full Flightradar24 experience free for 7 days
Remove ads and unlock over 50 additional features
On The Radar Logo

Get the Flightradar24 Aviation newsletter

Flight tracking and aviation industry news direct to your inbox

Aviation news comes quickly, so we want to bring more of the aviation world to you with our weekly Flightradar24 aviation newsletter - On The Radar.

On The Radar Logo