What squawk code is used to indicate lost communications?

The squawk code used to indicate lost communications is 7600. This code is specifically assigned for situations where an aircraft is unable to communicate with air traffic control due to radio failure. When a pilot sets their transponder to code 7600, it alerts air traffic controllers that they should be aware of the communication issue, allowing them to provide the necessary assistance or monitoring until communication can be re-established.

In the context of air traffic management, different squawk codes serve distinct purposes. For instance, code 7500 is reserved for indicating hijacking or unlawful interference, while code 7700 signifies an emergency situation that may not necessarily relate to a loss of communications. The code 9999 is not an officially recognized squawk code and does not serve a specific purpose in air traffic control. Understanding these codes is essential for effective communication and ensuring safety in airspace operations.