What does SSR stand for and what information does it provide?

• A. Secondary Surveillance Radar; it provides altitude only.
• B. Standard Signal Radar; it provides range and bearing.
• C. Satellite Surveillance Radar; it provides position.
• D. Secondary Surveillance Radar; it interrogates aircraft transponders to provide identity and altitude (and other data).

Answer: (D)

SSR stands for Secondary Surveillance Radar. It works by sending an interrogation to the aircraft’s transponder; the transponder replies with encoded information. This data typically includes the aircraft's identity (the squawk code or flight ID) and altitude (Mode C). More advanced transponders (Mode S) can provide additional data such as flight ID, speed, and other parameters. In short, SSR adds identification and altitude information to radar surveillance by querying the aircraft’s transponder, rather than relying on the radar’s own echo alone.