In lost communications procedures, what transponder code should be squawked?

When a pilot experiences lost communications and is unable to establish contact with air traffic control, the appropriate transponder code to squawk is 7600. This code specifically indicates to air traffic controllers that the aircraft is experiencing a radio communication failure.

By squawking 7600, you are effectively signaling to ATC that while your aircraft is still operational, you cannot communicate with them via radio. This allows air traffic control to adjust their radar watch and provide necessary support for the aircraft to safely continue its flight or to follow a predetermined procedure for lost communications.

In contrast, the other codes signify different scenarios: 7500 is used for indicating a hijacking situation, 7700 is for general emergency, while 7800 is not a standard transponder code used in aviation. Thus, squawking 7600 is critical for ensuring both the safety of the flight and the awareness of air traffic control regarding your communication status.