Garmin GTS 825 Pilots Guide - Page 12

Operation GTS 8XX Series Traffic The Garmin GTS 8XX Series unit is a Traffic Advisory System (TAS - GTS 800 and GTS 820) or Traffic Alert and Collision Avoidance System (TCAS I - GTS 850). The GTS 8XX Series enhances flight crew situational awareness by displaying traffic information for transponder-equipped aircraft. The GTS 8XX Series also provides visual and aural traffic alerts including voice announcements to assist in visually acquiring traffic. The GTS 800 and GTS 820 are TAS systems, the GTS 850 is a TSO-approved TCAS I system. The GTS 8XX uses active interrogations of Mode A/C/S transponders to provide Traffic Advisories. Theory of Operation When the GTS 8XX Series is in Operating Mode, the unit interrogates the transponders of intruding aircraft while monitoring transponder replies. The GTS 8XX Series uses this information to derive the distance, relative bearing, and if reported, the altitude and vertical trend for each aircraft within its surveillance range. The GTS 8XX Series then calculates a closure rate to each intruder based on the projected Closest Point of Approach (CPA). If the closure rate meets the threat criteria for a Traffic Advisory (TA), visual and aural alerting is provided. TAS/TCAS Surveillance Volume The GTS 8XX Series surveillance system monitors the airspace within ±10,000 feet of own altitude. Under ideal conditions, the unit scans transponder traffic up to 40 NM (GTS 820 and GTS 850) or 12 NM (GTS 800) in the forward direction using top and bottom-mounted antennas similar to TCAS II systems. In areas of greater transponder traffic density or when TCAS II systems are detected, the GTS 820 and GTS 850 systems automatically reduce interrogation transmitter power (and therefore range) in order to limit potential interference from frequency congestion. The GTS 800's range is 12 NM in the forward direction and the maximum interrogation transmitter power remains constant. There is also a minimum alerting threshold for range to allow alerting in situations where traffic is slowly converging. Alerting may be caused by closure rate or minimum distance to the intruder. 8 Garmin GTS 8XX Series Traffic Advisory System 190-00587-02 Rev. A