Garmin GPSMAP 496 Owner's Manual (for North America) - Page 157

TIS information is collected one radar scan prior to the scan during which the uplink occurs. Therefore, the surveillance information is approximately 5 seconds old. In order to present the intruders in a "real time" position, the TIS ground station uses a "predictive algorithm" in its tracking software. This algorithm uses track history data to extrapolate intruders to their expected positions consistent with the time of display in the cockpit. Occasionally, aircraft maneuvering causes this algorithm to induce errors in the GPSMAP 496 screen. These errors primarily affect relative bearing information and traffic target track vector (it will lag); intruder distance and altitude remains relatively accurate and may be used to assist in "see and avoid." Some of the more common examples of these errors include: • When client or intruder aircraft maneuvers excessively or abruptly, the tracking algorithm can report incorrect horizontal position until the maneuvering aircraft stabilizes. • When a rapidly closing intruder is on a course that crosses the client aircraft course at a shallow angle (either overtaking or head on) and either aircraft abruptly changes course within ¼ nm, TIS may show the intruder on the opposite side of the client than it actually is. • TIS > TIS Limitations These are relatively rare occurrences and are corrected in a few radar scans once the course has stabilized. Users of TIS can render valuable assistance in the correction of malfunctions by reporting their observations of undesirable performance. Reporters should identify the time of observation, location, type and identity of aircraft, and describe the condition observed; the type of transponder processor and software in use can also be useful information. Since TIS performance is monitored by maintenance personnel rather than ATC, it is suggested that malfunctions be reported in the following ways: • By telephone to the nearest Flight Service Station (FSS) facility. • By FAA Form 8000-7, Safety Improvement Report, a postagepaid card designed for this purpose. These cards can be obtained at FAA FSSs, General Aviation District Offices, Flight Standards District Offices, and General Aviation Fixed Based Operations. GPSMAP 496 Owner's Manual 149