Definition
A free ground-based service, available within the service volume of an ADS-B ground station, that uplinks traffic information about non-ADS-B-equipped aircraft to properly equipped ADS-B In aircraft. Ground radar detects these aircraft and the ADS-B ground network rebroadcasts their position, altitude, and movement so that ADS-B In equipped pilots see them on a cockpit display alongside ADS-B-equipped traffic.
Plain English
A free service that uses ground radar to spot aircraft that don't have ADS-B and then broadcasts their positions to your cockpit display, so you can still see them as traffic.
Context Anchor
You encounter TIS-B when using ADS-B In traffic information on a cockpit display or portable flight display.
Derivation
The name describes the function: it is a Traffic Information Service that is Broadcast from the ground, rather than addressed to a single aircraft. The 'Broadcast' part distinguishes it from the older TIS service, which sent traffic data to one aircraft at a time through a Mode S transponder link.
Why Pilots Care
It fills gaps in traffic awareness where not all aircraft broadcast their positions, helping pilots maintain separation and avoid conflicts.
Analogy
Think of it like a traffic report sent to your airplane: the ground system gathers what it can see nearby and broadcasts useful traffic information to aircraft that can receive it.
Grounding Statement
On a traffic display, TIS-B can make another airplane appear even when that airplane is not sending its own ADS-B position directly.
Intuition Check
Do not assume TIS-B shows all traffic. It only shows traffic the system can detect and send to your aircraft.
Example Sentence 1
Thanks to TIS-B, the pilot saw a nearby aircraft on the cockpit display even though that aircraft wasn't broadcasting ADS-B Out.
Example Sentence 2
TIS-B provided position data for non-equipped aircraft that the pilot would not otherwise have seen.