Definition
ADS-B In is the function of an aircraft avionics system that receives ADS-B broadcasts from other aircraft and from ground-based services. These broadcasts can include position, velocity, and identification data from nearby traffic (TIS-B and ADS-B traffic), as well as graphical and textual weather, NOTAMs, and other flight information transmitted through Flight Information Service-Broadcast (FIS-B). ADS-B In is not required by regulation in U.S. airspace; it is an optional capability that complements the mandatory ADS-B Out function.
Plain English
ADS-B In is the part of the aircraft's equipment that listens. It picks up signals from other aircraft and from ground stations, and shows the pilot things like nearby traffic and weather on a cockpit display.
Context Anchor
You will see this term in avionics equipment descriptions, traffic and weather display discussions, and aircraft equipment planning.
Derivation
Automatic — happens on its own without pilot action. Dependent — the data depends on the aircraft's own navigation system (usually GPS) to know where it is. Surveillance — watching or tracking aircraft. Broadcast — sent out openly for anyone in range to receive. The word 'In' simply means this is the receiving direction, as opposed to 'Out,' which transmits.
Why Pilots Care
Gives pilots direct awareness of nearby traffic and weather, reducing reliance on ground radar and improving safety in busy airspace.
Analogy
ADS-B Out is like speaking your position over a shared channel. ADS-B In is like listening to that channel and seeing useful information appear on your display.
Intuition Check
Do not confuse ADS-B In with ADS-B Out. ADS-B In receives information for the pilot to see; ADS-B Out transmits your aircraft’s information for others to use.
Example Sentence 1
With ADS-B In installed, the pilot could see nearby traffic on the tablet display long before ATC called the traffic.
Example Sentence 2
Automatic dependent surveillance broadcast in provided the crew with current weather imagery while crossing the mountains.