SSR stands for Secondary Surveillance Radar.

• A. Secondary Surveillance Radar
• B. Satellite Surveillance Radar
• C. Signal Surveillance Radar
• D. Standard Surveillance Radar

Answer: (A)

In air traffic control, radar systems come in two main kinds: primary radar, which detects aircraft by reflected energy, and secondary radar, which relies on a transponder aboard the aircraft to actively reply to interrogations. SSR stands for Secondary Surveillance Radar—the system that identifies each aircraft and provides altitude information by querying the aircraft’s transponder (Mode A/C/S). The term “secondary” indicates it depends on cooperation from the aircraft, unlike primary radar that works without any transponder. The other expansions aren’t used in aviation terminology: satellite surveillance radar would imply space-based radar, which isn’t the standard ATC term; signal surveillance radar and standard surveillance radar aren’t recognized names for this system. That’s why Secondary Surveillance Radar is the correct interpretation.