Definition
A surveillance system in which an aircraft automatically broadcasts its position, altitude, velocity, and identification, derived from onboard navigation sources (typically GPS), at regular intervals. The broadcast is received by air traffic control ground stations and by other suitably equipped aircraft, without any interrogation from the ground.
Plain English
Your aircraft figures out where it is using GPS and constantly tells everyone — controllers and nearby planes — its position, altitude, speed, and ID. Nobody has to ask; the aircraft just keeps broadcasting.
Context Anchor
You will see ADS-B in aircraft equipment requirements, traffic displays, flight planning, airspace rules, and discussions about how air traffic control tracks aircraft.
Derivation
Each word explains a piece of how the system works. Automatic — the aircraft sends its data on its own, with no pilot or controller action required. Dependent — the data depends on the aircraft's own navigation system (usually GPS) being accurate. Surveillance — it is used to keep track of where aircraft are. Broadcast — the information is sent out to anyone listening, not directed at one receiver.
Why Pilots Care
ADS-B is required in most controlled airspace, supports more precise air traffic separation, and enables cockpit traffic and weather displays when the aircraft also has ADS-B In capability.
Analogy
It is like an aircraft continually announcing, “Here I am, this is my height, this is my speed, and this is my identity,” over a radio channel that controllers and equipped aircraft can receive.
Intuition Check
Do not read “dependent” as meaning weak or optional. In ADS-B, it means the system depends on the aircraft’s own navigation equipment for the position it broadcasts.
Example Sentence 1
Before flying into Class B airspace, the pilot confirmed the aircraft's ADS-B Out was operating and transmitting correctly.
Example Sentence 2
ADS-B In on the electronic flight bag showed three nearby aircraft that were not yet visible to the crew.