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Traffic information service – broadcast is an aviation information service that allows pilots to see aircraft that are not emitting ADS-B data but have a basic transponder.
As aircraft are discovered by primary radar and respond with encoded altitude information, this information is broadcast over ADS-B. These near real time positions and ground track in 45 degree increments of other nearby aircraft are received as either a "traffic advisory" or "proximate" intruder, for the purposes of collision avoidance. It presents to the pilot a combined representation of aircraft positions derived from GPS satellite and ground-based radar data, specifically: aircraft's replies to ATC interrogations.
TIS-B is broadcast to aircraft using both the 1090 MHz extended squitter and the universal access transceiver band of Automatic Dependent Surveillance–Broadcast. Currently the service mainly benefits general aviation aircraft equipped with ADS-B "in" hardware by providing a traffic information relay to a screen in the cockpit. In order to use TIS, the client and any intruder aircraft must be equipped with the appropriate cockpit equipment and fly within the radar coverage of a Mode S radar capable of providing TIS. Typically, this will be within 55 NM of these sites.
At this time TIS–B is meant to be only a supplement to visual separation from other aircraft when operating in visual meteorological conditions and as a backup to radar, which in remote areas only updates every 13 seconds, when operating under instrument flight rules.