Definition
A surveillance technology in which an aircraft automatically and continuously transmits its own position, altitude, velocity, and identification, derived from onboard navigation sources such as GPS, to ground stations and other suitably equipped aircraft. The transmission requires no interrogation from radar or controllers and is broadcast openly for any qualified receiver to use.
Plain English
The aircraft works out where it is using GPS and constantly tells everyone — air traffic control and nearby aircraft — its position, altitude, and speed. No one has to ask; the aircraft just keeps broadcasting it.
Context Anchor
Seen in instrument flying, traffic displays, air traffic control services, and equipment requirements for certain controlled airspace.
Derivation
The name describes how it works. Automatic — it sends the data on its own, with no pilot or controller action. Dependent — it depends on the aircraft's own navigation equipment (usually GPS) for the position data. Surveillance — it serves the same purpose as radar surveillance: knowing where aircraft are. Broadcast — the information is sent out openly, not to a single recipient. Reading the name in this order makes the function clear.
Why Pilots Care
It improves traffic awareness in the cockpit and meets airspace requirements that enhance separation and safety.
Analogy
ADS-B is like an aircraft sending a regular location update: “This is who I am, this is where I am, and this is how I’m moving.” Other approved systems can use that update to build a traffic picture.
Intuition Check
“Automatic” does not mean the airplane flies itself; it means the position reports are sent automatically. “Dependent” does not mean unreliable; it means the report depends on the aircraft’s own position source.
Example Sentence 1
Before entering the Class B airspace, the pilot confirmed the ADS-B Out transponder was transmitting correctly.
Example Sentence 2
ADS-B broadcasts the airplane's position once per second during cruise.