Ads-B In Alerting - Garmin GTS 820 TAS Pilot's Manual

6.4.2 ADS-B In Alerting

To be tracked with active surveillance, an intruder aircraft must receive
interrogations and transmit replies. If the intruder aircraft does not detect
interrogations (e.g. it is too far to receive interrogations), it cannot be tracked by
GTS active surveillance. When ADS-B In is installed and active, GTS may receive
ADS-B, ADS-R, or TIS-B for an intruder aircraft that can't be tracked with active
surveillance. Such targets are tracked with ADS-B In only, and are included in
the display of traffic. GTS will also generate alerts for targets tracked with ADS-B
In only.
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Garmin GTS Traffic Systems 190-00587-02 Rev. E