Which squawk code should be transpondered to indicate lost communications?

The appropriate transponder code to indicate lost communications is 7600. This code is part of the standard squawk codes used in aviation to convey specific situations to air traffic control and other aircraft.

When a pilot has lost communication with air traffic control, using the squawk code 7600 signals to ATC that the aircraft is experiencing a communications failure. It enables controllers and nearby aircraft to understand the situation and provide the necessary assistance or avoid assumptions regarding the flight’s intentions.

This code does not imply an emergency such as a hijacking (which is indicated by 7500) or a general emergency situation (which is indicated by 7700). Instead, it specifically addresses communication issues, allowing for the appropriate response from air traffic services. Understanding the purpose of these codes is essential for pilots, as it ensures clarity in their communication and situational awareness among all entities involved in aviation safety.