What does squawking 7600 indicate?

• A. Radar contact lost.
• B. Transponder test mode.
• C. ATC priority handling.
• D. Radio failure.

Answer: (D)

Squawking 7600 means a radio communications failure. Pilots set this specific transponder code to signal to air traffic control that they cannot establish two-way voice contact. With that code, ATC knows the reason for the loss of communications and will apply lost-communications procedures while continuing to manage traffic around the aircraft.

This is different from emergency (7700), which indicates a broader in-flight emergency, and from hijack (7500), which signals a security threat. “Radar contact lost” is a controller observation, not the purpose of a transponder code. The code for a radio failure tells ATC to expect the aircraft to continue the flight using non-voice methods and to follow established lost-communications procedures, such as continuing via the last assigned route and altitude, or the route/altitude expected or filed, depending on the flight rules in effect.