A Look At The World Of Squawk Codes And Their Meanings

If you have a keen interest in the wonderful world of aviation, or like listening to inflight air traffic control (ATC) communications, you've likely heard of 'squawk codes.' These are four-digit codes given by ATC to all aircraft in the airspace for communication purposes. However, squawk codes can also be used for various different important communications between aircraft and the ground.

Key to communication

The primary goal of a squawk code is to provide effective communication between the ATC and the aircraft. Prior to departure, aircraft will be given squawk codes, which will be used by ATC to direct the aircraft during its flight. This code will show up on ATC screens and helps provide basic information such as speed and altitude. Squawk codes are four digits, with each being a number between zero and seven.

This gives thousands of possible combinations for air traffic controllers to give to the aircraft under their control. That being said, there are actually certain combinations that can't be used, and for good reason, as well. This is because there are a few reserved squawk codes, which we'll come to a bit later. Pilots have to enter squawk codes into their transponders to communicate with flight controllers.

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Therefore, only if the correct squawk code is entered into the transponder will it appear on ATC screens with the correct information. The transponder is constantly communicating with the ground and providing "pings" with information. At times, aircraft might be asked to change their squawk codes once they become airborne.

There are several reasons why this can be the case. For example, the purpose of such a switch might be to better communicate with other towers. Alternatively, this can also be required if entering restricted airspace. This means a flight might have multiple squawk codes depending on where it is flying and on what path.

Ensuring safety and separation

As we are all well aware, the world of aviation is an industry that is driven primarily by safety-based practices. It comes as no surprise that squawk codes are no exception to this ethos. These four-digit codes are very important to ensure aircraft separation, especially during the takeoff and landing phases of a given flight.

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Air traffic control uses squawk codes to monitor aircraft positions on information screens, ensuring that they do not break minimum separation while flying. Having the transponder off or inputting incorrect squawk codes has the potential to result in a safety threat and security situation, as has happened in the past. Collisions between aircraft can be deadly, so keeping them suitably separated is vital.

In this vein, squawk codes are particularly helpful in crowded airspace, as, under such conditions, air traffic controllers have the busy task of managing multiple aircraft simultaneously. Since most arrival and departure paths are already set, the corresponding controllers must ensure that there are no aircraft in the vicinity.

Emergency codes

Perhaps the most publicly known squawk codes are those used for emergency conditions, which we often come across in news coverage of instances when a flight's safety has been compromised. These three ICAO-assigned squawk codes can be used by any aircraft with a transponder to explain their emergency to controllers.

The first emergency code that you may have become familiar with is Squawk 7500. This code is used to indicate that the aircraft has been hijacked, and therefore requires urgent emergency support from both security services and air traffic control. This code has become particularly popular thanks to cinema and pop culture. Flight 7500 in 2014 references the code for a supernatural film, while the movie 7500 uses the squawk code while depicting a hijacking onboard.

However, the code has been used in real life too. In 2019, the pilot of an Air Europa A330 accidentally entered the Squawk 7500 during the boarding process while teaching an intern, according to One Mile At A Time. Instantly, the airport went into lockdown, with police deployed all over, flights moved away, and the terminal cleared, some fake news about three travelers with knives only made the matter more confusing. Thankfully, all was cleared up within hours, and was there no threat.

The second emergency code is Squawk 7600. This code is used to communicate to air traffic controllers that the aircraft in question has lost communication with the tower. In the case that contact cannot be established, planes will be directed using aviation light signals. These light signals can be used to provide aircraft with clearance to land or to indicate unsafe conditions in these cases. While more common than 7500, these are always reserved when no backup communication method is available and the aircraft requires information.

The third emergency code is Squawk 7700, which is used to communicate all emergencies onboard a flight, and is perhaps the best-known example. Depending on the nature and severity, crews may conduct checks before formally declaring an emergency. When Squawk 7700 is declared, all nearby ATCs are also informed of the emergency and pilots can fly the plane as they see fit. Squawk 7700 occurs more commonly than you might expect, with pilots using the code to quickly notify ATC that they require assistance and have pressing issues onboard or with the aircraft.

Credit: Photo: Peter Krocka/Shutterstock

An alarming misunderstanding

An incident that stands out with squawk codes occurred during the 9/11 attacks on September 11th, 2001. On this fateful day in the history of commercial aviation, a Korean Air flight from Seoul to New York was forced to divert to Whitehorse Airport in Yukon, Canada following a miscommunication over squawk codes.

In a message from the Korean Air flight, the pilot included "HJK" in the message, a code for a hijacking. As such, the company subsequently notified NORAD of the possible situation. ATC then asked the flight to change its squawk code to 7500, the code for hijacking, as a way to check if the plane was indeed hijacked.

The flight crew changed the squawk code without any protest, unknowingly confirming suspicions that the plane might be hijacked. In reality, the plane was not hijacked and the change in squawk code had been done without understanding the meaning of the code. Considering the four plane hijackings and crashes just hours earlier, it was unsurprising the measures that had to be taken.

The possible hijacking caused massive panic, and led to certain cities in Alaska being evacuated. Furthermore, the Canadian Prime Minister authorized the plane to be shot down if it did not comply with orders from NORAD. Eventually, the plane landed safely and it was determined there was no hijacking onboard. However, the incident became prominent and was a lesson in the importance of squawk codes, especially in the post-9/11 environment.

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Serving an important purpose

More recently, Simple Flying also covered a story involving a brand-new Air France Airbus A220 that squawked 7700 in November 2021. The crew declared the emergency shortly after takeoff, with the airline later confirming that the situation arose as a result of a pressurization malfunction. The jet safely returned to Paris soon after.

A year later, in December 2022, a British Airways A320 declared an emergency and returned to London Heathrow, with passengers reporting a smell in the cabin and pilots donning oxygen masks. The airline didn't reveal the exact malfunction and the incident was ruled out as precautionary. The uses for Squawk 7700 can vary significantly, but it does put all nearby ATCs on high alert and gives pilots more flexibility to operate.

Overall, squawk codes serve an important purpose in ensuring strong communication and safety between the ground and aircraft. With more and more congested airspace, it remains important that squawk codes are correctly followed by air traffic controllers and flight crews. On your next flight, be sure to find out your plane's squawk code, and follow along with ATC communications with ease! Some airlines, like United, even allow you to tune into radio communications in real-time, letting you keep track of the ongoings with ATC. Hopefully you won't see any of the three reserved squawk codes on there!

Did you know about the ins and outs of squawk codes? Have you ever been onboard a flight that has used one of the reserved examples? Let us know your thoughts and experiences in the comments.

Source: One Mile At A Time