Definition
A function of an aircraft's onboard avionics that automatically broadcasts the aircraft's GPS-derived position, altitude, velocity, identification, and other flight data once per second over a dedicated radio link, without any action by the pilot and without requiring an interrogation from ground radar. The broadcast is received by air traffic control ground stations and by other suitably equipped aircraft.
Plain English
Equipment on the aircraft that automatically tells everyone else where it is. Once per second, it sends out its position, altitude, speed, and ID so controllers and nearby aircraft can see it. The pilot does not have to do anything for this to happen.
Context Anchor
You will see this term in aircraft equipment requirements, airspace entry planning, avionics setup, and discussions of whether an aircraft is allowed to operate in certain areas.
Derivation
Each word describes how the system works. Automatic — it runs on its own. Dependent — it depends on the aircraft's own navigation source (GPS) to know where it is, rather than being tracked from the ground. Surveillance — it lets others watch the aircraft's position. Broadcast — it sends the data out to anyone listening, rather than replying to a specific request. OUT — the data is going out from the aircraft (as opposed to ADS-B IN, which receives data).
Why Pilots Care
ADS-B OUT is mandatory for operations in most controlled airspace, directly supporting traffic separation and collision avoidance.
Analogy
It is like the aircraft continually sending a short digital “here I am” message to the traffic system around it.
Intuition Check
OUT does not mean the pilot is making a radio call outward. Here, OUT means the aircraft equipment is automatically transmitting flight information from the aircraft to receivers outside the aircraft.
Example Sentence 1
Before entering Class B airspace, the pilot confirmed the aircraft's ADS-B OUT was transmitting correctly.
Example Sentence 2
With ADS-B OUT active, nearby traffic received accurate position broadcasts from the aircraft.