Definition
A surveillance system in which an aircraft automatically broadcasts its own position, altitude, velocity, and identification, derived from onboard navigation sources such as GPS, on a regular schedule. Ground stations and other suitably equipped aircraft receive these broadcasts and use them for traffic surveillance and separation. ADS-B Out is the transmitting function, mandated in defined U.S. airspace; ADS-B In is the receiving function, which allows the cockpit to display nearby traffic and certain weather and flight information services.
Plain English
The aircraft figures out where it is using GPS and constantly tells everyone — air traffic control and nearby aircraft — its position, altitude, and speed. Other aircraft equipped to receive these signals can see that traffic on a cockpit display.
Context Anchor
Seen in flight plan equipment codes, aircraft equipment checks, airspace requirements, and discussions of modern air traffic surveillance.
Derivation
Each word describes how the system works. Automatic — it transmits on its own without the pilot triggering it. Dependent — it depends on the aircraft's own navigation equipment (mainly GPS) to know its position; the ground station does not measure the position itself the way radar does. Surveillance — it is used for tracking aircraft. Broadcast — the signal goes out to anyone listening, not just to one receiver. Together, the name is a literal description of the function.
Why Pilots Care
ADS-B improves traffic awareness and is required equipment for many airspace operations, directly affecting access to routes and safety margins.
Intuition Check
Do not read “dependent” as meaning unreliable or secondary. In ADS-B, “dependent” means the system depends on the aircraft’s own equipment to know and report its position.
Example Sentence 1
Before departing into Class B airspace, the pilot confirmed the ADS-B Out transponder was operating and transmitting a valid position.
Example Sentence 2
ADS-B Out allowed ATC to track the departure precisely without radar coverage.