How is altitude information obtained in secondary radar systems?

• A. By using the ground-based radar signal
• B. By using the aircraft's transponder to report its altitude
• C. Through visual observation from the control tower
• D. By measuring with onboard altimeters

Answer: (B)

In secondary radar systems, altitude information is obtained primarily through the use of the aircraft's transponder. When an aircraft is flying, its transponder actively responds to interrogation signals sent by ground-based radar systems. This response includes various data, one of which is the aircraft's altitude information, relayed in a coded format.

The transponder measures altitude using the aircraft's onboard altimeter system and transmits this data back to the radar system whenever it is queried. This process allows air traffic controllers to have real-time altitude data for all aircraft equipped with transponders in their airspace, improving situational awareness and safety.

Other methods for obtaining altitude information, such as visual observation from control towers or measuring with onboard altimeters alone, do not provide the real-time, automated responses required for efficient air traffic management, and ground-based radar signals do not inherently contain altitude data without the transponder's input.