Which description corresponds to Automatic dependent surveillance—broadcast (ADS-B)?

• A. A ground-based navigation signal receiver.
• B. A weather data transmission system.
• C. A flight management system.
• D. A function on an aircraft or vehicle that periodically broadcasts its state vector and other information.

Answer: (D)

ADS-B is an airborne surveillance method where the aircraft automatically determines its own position and other data from on-board navigation sensors (usually GPS) and periodically broadcasts that information to air traffic control and to other equipped aircraft. The key idea is that the airplane is both dependent on its own sensors to know its state (location, speed, altitude, etc.) and automatic in transmitting that state to others, rather than relying on ground-based radar alone or on a ground transmitter.

The description that fits describes a function on the aircraft that periodically broadcasts its state vector and other information. The state vector includes where the aircraft is (position), how fast and in what direction it’s moving (speed and heading), and how high it is (altitude), along with other data such as identification and advisory status. This is what enables ATC and other pilots to see the aircraft on ADS-B displays without continuous radar contact.

Other options don’t describe ADS-B: it isn’t a ground-based navigation signal receiver like VOR/LOC systems, it isn’t primarily a weather data transmission system, and it isn’t the flight management system itself.