What squat code is used for lost communications?

The squat code used for lost communications is 7600. This code is part of the transponder squawk system, which provides a way for pilots to communicate their aircraft's status to air traffic control without using radio communication. When a pilot experiences a loss of communications, squawking 7600 alerts air traffic controllers that the aircraft is unable to communicate and they can take appropriate measures to ensure the safety of the flight.

Understanding the context of all the other codes helps clarify this: 7500 indicates unlawful interference, such as hijacking; 7700 is used for general emergencies, indicating that the aircraft is in some form of distress; and 7800 is not a standard squawk code used within this context. Therefore, 7600 is specifically designated for situations involving lost communications, clearly indicating to air traffic control the nature of the issue the pilot is facing.