How does secondary surveillance radar (SSR) enhance ATC surveillance?

• A. It interrogates aircraft transponders to obtain identity data and altitude (Mode C), supplementing PSR with cooperative data.
• B. It detects aircraft passively from reflections, without transponders.
• C. It increases radar power to extend range.
• D. It provides weather data through reflectivity patterns.

Answer: (B)

Secondary surveillance radar enhances ATC by actively querying aircraft transponders to obtain cooperative data such as identity and altitude (Mode C), which supplements the position information obtained from primary radar. The ground station sends an interrogation signal to the aircraft; in response, the transponder on board replies with encoded data that identifies the aircraft and reports altitude, allowing controllers to positively identify aircraft and maintain precise vertical separation. This cooperative data makes tracking more reliable and reduces ambiguity in the radar picture. It is not a passive detection method, and it does not increase radar power or provide weather information.