Squawk codes explained: 1200, 7500, 7600, 7700 and more

6 min read · Updated October 11, 2026

What a squawk is

A squawk code is a four-digit code dialled into an aircraft's transponder. When ground radar interrogates the transponder, it replies with that code, and modern transponders include it in their ADS-B broadcasts too. Air traffic control uses it to link a radar target to a flight plan.

Each digit runs from 0 to 7, because the code is octal. That gives 4,096 possible codes, from 0000 to 7777. The term "squawk" comes from an old military code word, and controllers still say it: "United 452, squawk 3421."

Most codes are discrete codes assigned by a computer for one flight in one region. They have no meaning outside that context. A plane showing 4615 tells you nothing special. A handful of codes, though, are reserved and do mean something.

The reserved codes worth knowing (US)

Outside the US the conventions differ. In Europe and many other places, VFR aircraft squawk 7000 rather than 1200, and 2000 is used by aircraft entering radar airspace without an assigned code. The three emergency codes, 7500, 7600 and 7700, are the same worldwide.

1200: the everyday VFR code

If you see a small plane on the map squawking 1200, it is flying under visual flight rules and probably not talking to air traffic control. That is completely normal. Weekend pilots, flight students and sightseeing flights often squawk 1200. Most small aircraft you see under 10,000 ft away from big airports will show it.

7700: general emergency

A pilot sets 7700 to declare an emergency, or a controller may ask for it. It instantly flags the aircraft on every radar screen and alerts receivers in the ADS-B network. Reasons can include:

• A medical emergency on board, which is one of the most common causes.
• A technical problem: an engine shutdown, a pressurisation issue, a hydraulic or electrical fault, a warning light that needs checking.
• Smoke or a fumes smell in the cabin.
• Low fuel or a need for priority to land.

Many 7700 events are precautionary. Crews are trained to declare early so they get priority and room to work, and most of these flights land normally. Sometimes the pilot sets 7700 first and controllers later assign a regular code once they have the details, so the 7700 may disappear from the map while the aircraft is still diverting.

7600: radio failure

7600 means the crew cannot talk to air traffic control. Controllers then expect the aircraft to follow published lost-communications procedures, typically continuing on its cleared route and altitude and landing at the planned destination. It is often caused by a radio fault or a simple frequency mix-up and is usually resolved quickly, sometimes by passing messages through another aircraft or by phone after landing.

7500: unlawful interference

7500 is the hijack code. It is extremely rare in practice. When it does appear on public maps, it is more often a mistake, such as a pilot dialling the wrong number, than an actual hijacking. Controllers have procedures to confirm it discreetly, and a mistaken 7500 is usually corrected within moments. Military aircraft may be sent to check on any aircraft that continues to show it.

7400: lost link

7400 is used by remotely piloted aircraft, such as large military or government drones, when the link to the ground pilot is lost. The aircraft then flies a pre-programmed route. It is uncommon to see on public maps because most such aircraft fly in restricted areas.

What to think if you see 7700 on the map

1. Don't assume the worst. Most emergency squawks end with an uneventful landing, often at the original destination or a nearby airport.
2. Look at the flight path. A turn back toward the departure airport, a descent, or a diversion is common. Circling may mean the crew is working a checklist or reducing weight before landing.
3. Don't call emergency services because of a squawk. Air traffic control already knows, and the airport has arranged a response if one is needed.
4. Be careful sharing. There may be passengers' families watching. Facts first, speculation never.

The same applies to brief odd codes. When pilots change codes, older equipment may momentarily pass through other numbers, and flight-test and military flights sometimes use codes that look unusual.

Squawk, Mode C and ADS-B

Squawk codes date from radar transponders. A Mode C transponder sends the code plus pressure altitude; a Mode S transponder adds a unique aircraft address; and ADS-B adds GPS position, speed and identity. The squawk still exists alongside all of it. In the live sky tool you can see each aircraft's code where it is broadcast. For more on how the signals work, see how ADS-B works.

Other things pilots do with the transponder

• Ident: a button that briefly highlights the aircraft on the controller's screen, used when a controller says "squawk ident".
• Standby: the transponder is on but not replying, used on the ground at some airports.
• Altitude reporting off: a controller may ask a pilot to stop sending altitude if the readout looks faulty.

So the four digits are mostly bookkeeping. The ones to remember are 1200 for everyday flying and the three sevens for trouble.

Frequently asked questions

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