Garmin aera 796 Pilot's Manual page 168

Appendix F
• TIS operation may be intermittent during turns or other maneuvering.
• TIS is dependent on two-way, line-of-sight communications between the aircraft and
the Mode-S radar antenna. Whenever the structure of the aircraft comes between
the transponder antenna and the ground-based radar antenna, the signal may be
temporarily interrupted.
NOTE: Refer to the TIS Limitations section of the Aeronautical Information
Manual (AIM) for a more comprehensive explanation of limitations and
anomalies associated with TIS.
NOTE: TIS is unavailable at low altitudes in many areas of the United States.
This is often the case in mountainous regions.
NOTE: Garmin is not responsible for Mode S geographical coverage. Operation
of the ground stations is the responsibility of the FAA. Refer to the AIM for a
Terminal Mode S radar site map.
TIS information is collected during a single radar sweep. Collected information is
then sent through the Mode S uplink on the next radar sweep. Because of this, the
surveillance information is approximately five seconds old. TIS ground station tracking
software uses prediction algorithms to compensate for this delay. These algorithms use
track history data to calculate expected intruder positions consistent with the time of
display. Occasionally, aircraft maneuvering may cause variations in this calculation and
create slight errors on the Navigation Map which affect relative bearing information
and the target track vector and may delay display of the intruder information. However,
intruder distance and altitude typically remain relatively accurate and may be used to
assist in spotting traffic. The following errors are common examples:
• When the client or intruder aircraft maneuvers excessively or abruptly, the tracking
algorithm may report incorrect horizontal position until the maneuvering aircraft
stabilizes.
• When a rapidly closing intruder is on a course that intercepts the client aircraft
course at a shallow angle (either overtaking or head-on) and either aircraft abruptly
changes course within 0.25 nm, TIS may display the intruder aircraft on the incorrect
side of the client aircraft.
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Garmin aera 795/796 Pilot's Guide 190-01194-00 Rev. A