What is a squawk code?
A squawk is a four-digit number an aircraft sends from its transponder so air traffic control can tell it apart on radar.
The basics
Every aircraft with a transponder is given a four-digit code, each digit from 0 to 7. Controllers assign it, and the transponder broadcasts it along with the aircraft’s height.
Special codes
- 7700: a general emergency.
- 7600: radio failure. The crew cannot talk to air traffic control.
- 7500: unlawful interference, such as a hijack.
These three are the same around the world. Seeing 7700 on a map does not always mean a disaster: many are precautionary and end in a normal landing.
Some codes are standard in a region. In the UK, 7000 is commonly used by pilots flying visually without a controller. In the USA the equivalent is 1200.
Watch for it
Aircraft that squawk an emergency code are flagged by public tracking sites. Because the code is broadcast openly, anyone with a receiver can see it.