A Nuts-and-Bolts Guide to Transponder Codes (Bonus: Squawk Code PDF)

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Last updated 11 abril 2025

A Nuts-and-Bolts Guide to Transponder Codes (Bonus: Squawk Code PDF)

Today we’re digging into transponder codes and their usages. We will talk about the meanings of standard codes and emergency codes (plus which codes you are not allowed to use), then wrap up with tips and tricks for memorizing emergency transponder codes. We’ve also created a bonus downloadable squawk code pdf for you. What are Squawk Codes? A transponder code, or squawk code, is a four-digit numerical sequence a pilot enters into their radio transponder. There are 4,096 discrete squawk code possibilities ranging from 0000 to 7777. Each code combination is a unique identifier that allows air traffic controllers to keep track of individual aircraft. Mode A, Mode C, and Mode S transponders all use transponder codes to send their identification back to ATC. Mode C transponders also send aircraft pressure altitude. Mode S transponders are the most advanced, sending
Today we’re digging into transponder codes and their usages. We will talk about the meanings of standard codes and emergency codes (plus which codes you are not allowed to use), then wrap up with tips and tricks for memorizing emergency transponder codes. We’ve also created a bonus downloadable squawk code pdf for you. What are Squawk Codes? A transponder code, or squawk code, is a four-digit numerical sequence a pilot enters into their radio transponder. There are 4,096 discrete squawk code possibilities ranging from 0000 to 7777. Each code combination is a unique identifier that allows air traffic controllers to keep track of individual aircraft. Mode A, Mode C, and Mode S transponders all use transponder codes to send their identification back to ATC. Mode C transponders also send aircraft pressure altitude. Mode S transponders are the most advanced, sending not only a squawk code, identification, and pressure altitude, but also Automatic Dependent Surveillance Broadcasting (ADS-B), Traffic Collision Avoidance (TCAS), and enhanced surveillance data. How do you know what transponder code to use? If you are flying under visual flight rules in uncontrolled U.S. or Canadian airspace, you will use squawk code 1200. You may also hear this referred to as “squawk VFR.” If you’re in a controlled airspace, the controller will assign you a unique four-digit squawk code. Pro Tip: Make sure you enter your assigned squawk code correctly. If your entered code doesn’t match the one the controller gave you, they will tell you have an invalid transponder code. How do you enter a transponder code? To set your squawk, turn your transponder on and input either the code you’ve been given by ATC or the appropriate generic code for your airspace (ex-1200 for VFR flights in the United States). If you are in communication with ATC, they may also ask you to press the IDENT button when you set your assigned code. Pro Tip: If your transponder uses knob dials, be careful when changing your codes so you don’t accidently temporarily set your squawk code to one of the emergency codes (especially 7500) while scrolling through. Note that this isn’t an issue with button operated digital transponders because the code is not transmitted until you enter the fourth digit. What transponder codes are you not allowed to use? If you’re a civilian aviation pilot, two of the most important squawk codes to avoid are 0000 and 7777. Both codes are reserved for military interceptor operations. The three emergency squawk codes should also be avoided unless they apply to your situation. What are the 3 Emergency Squawk Codes? In coordination with the International Civil Aviation Organization (ICAO), the FAA has designated three emergency transponder codes that all pilots should memorize (though hopefully you will never have to use them). What does Squawk 7500 mean? A squawk of 7500 is the transponder code for hijacking. By discretely entering this squawk code, a pilot can let ATC know that the aircraft is no longer under their control. If you set this code, ATC will attempt radio contact to confirm you are squawking 7500. If they don’t hear from you, they will assume your plane is in fact hijacked. What does Squawk 7600 mean? A squawk of 7600 means lost radio communication. You should use this squawk code if you cannot receive, cannot transmit, or are completely unable to use your radio for either transmitting or receiving. Once you squawk 7600, ATC may ask you to “ident.” If you can receive but not transmit with your malfunctioning radio, pressing the “ident” button when instructed lets ATC know you can hear them but not reply verbally. Pro Tip: If your radio is completely inoperable, be visually alert as you make your approach to landing. Watch for the for light gun signals being used to communicate with you. What does a Squawk of 7700 mean? A squawk of 7700 is used for any emergency other than hijacking or lost radio communication. This code can include a broad range of situations like engine failure, fuel emergencies, flight control malfunctions, severe icing, landing gear malfunctions, airframe damage, fire, pressurization failure, onboard medical emergencies, and more. Squawking 7700 immediately grabs the attention of ATC. If your radio is working, the controller will want you to share important information like your aircraft registration number, your current position, planned destination, nature of the problem, how many souls are on board, what your fuel reserves are, and your intentions. Remember, as pilot in command, you remain the final authority for aircraft operation throughout the emergency. You are authorized to deviate from CFRs as justifiably needed to safely operate and land the aircraft. ATC will do everything they can to clear traffic out of the way and help you throughout the emergency. Are Transponder Codes the Same in Every Country? If you’re flying internationally, you need to know that the use of each squawk code varies by country. Although there are a few ICAO designated codes (more on that in a minute) there is no global standard for every single transponder code assignment. Consult the Aeronautical Information Manual (AIM) for other countries you will be flying in to learn their generic squawk code assignments. Complete List of ICAO Squawk Codes and their Meanings The International Civil Aviation Organization (ICAO) has a list of six transponder codes that have been standardized for global use. They are: 1000: Mode A transponder code that is reserved for use in Mode S radar/ADS-B setups where aircraft identification is used to correlate flight plan 2000: Uncontrolled IFR transponder code used when entering a secondary surveillance radar (SSR) area from a non-SSR area 7000: Standard VFR transponder code to be used when no other code has been assigned 7500: Aircraft hijacking 7600: Radio failure 7700: General Emergency How do you Remember Transponder Codes? The good news is that while it might be fun to read the full list of transponder codes and their meanings, you don’t need to memorize them all (unless you want to annihilate the competition at your next round of hangar bar aviation trivia). Start by learning the three emergency codes since they are the most critical. (Just ask the pilots of Korean Air Flight 085). After that, move on to the most common standard local and ICAO codes. Today’s student pilots can thank the seasoned aviators who came before them for coming up with all sorts of methods to memorize the three all-important emergency squawk codes. We like the Pilot Institute’s 3 easy ways to remember squawk codes. They include the rhyming method, all in one sentence, and acronym. If you know the frequencies in order (7500, 7600, 7700) the sentence method is easy to use and recall. Just remember: “Hi Jack, I can’t talk; there’s an emergency.” If you want help remembering both the squawk codes and their meanings, the rhyming method will probably be more useful for you. Want to learn more about aircraft transponders? Check out these posts. Aircraft Transponders: What Type do You Need (And What’s the Difference?) GPS & ADS-B Portable Buyers Guide What do you need to do to get your aircraft compliant with the 2020 ADS-B requirement?