What is a transponder?

What is a transponder?

• A. A radio or radar set that emits a radio signal after receiving such a signal.
• B. A device that receives GPS signals to determine position.
• C. An aircraft lighting system for signaling.
• D. A system that transmits weather data to ground stations.

Answer: (A)

A transponder is a radio device on an aircraft that automatically replies to a radar interrogation with a coded response. It listens for a question from air traffic control radar and then emits a reply, often including the aircraft’s identity and altitude, enabling the radar system to identify and track it on secondary surveillance radar. This distinguishes it from a GPS receiver (which determines position from satellites), an aircraft lighting system (for signaling), or a weather data link (transmitting weather information). The transponder doesn’t initiate transmission on its own; it responds when queried.

A transponder is a radio device on an aircraft that automatically replies to a radar interrogation with a coded response. It listens for a question from air traffic control radar and then emits a reply, often including the aircraft’s identity and altitude, enabling the radar system to identify and track it on secondary surveillance radar. This distinguishes it from a GPS receiver (which determines position from satellites), an aircraft lighting system (for signaling), or a weather data link (transmitting weather information). The transponder doesn’t initiate transmission on its own; it responds when queried.