Which information does Secondary Surveillance Radar (SSR) provide that Primary Surveillance Radar (PSR) does not?

• A. Ground speed.
• B. Identity and altitude from aircraft transponders.
• C. Wind speed.
• D. Terrain clearance.

Answer: (B)

Primary Surveillance Radar provides position by detecting echoes and showing where an aircraft is, but it doesn’t tell you who the aircraft is or how high it is. Secondary Surveillance Radar works by interrogating the aircraft’s transponder, and the transponder replies with two key pieces of data: an identity (the discrete code that identifies the aircraft) and altitude information (from Mode C or related altitude reporting). This combination lets air traffic controllers know exactly who is up there and at what altitude, which PSR alone cannot provide.

Other options don’t fit because wind speed, terrain clearance, and ground speed aren’t derived from the transponder interrogations SSR uses; wind and terrain data come from separate sensing or data sources, and ground speed is not the primary information SSR transmits.