Garmin GTN 750 Pilot's Manual page 216

NOTE: TIS will be unavailable at low altitudes in many areas of the U.S.,
Foreword
particularly in mountainous regions. Also, when flying near the "floor" of
radar coverage in a particular area, intruders below the client aircraft may
Getting
Started
not be detected by TIS.
Audio &
TIS information is collected one radar scan prior to the scan during which
Xpdr Ctrl
the uplink occurs. Therefore, the surveillance information is approximately
Com/Nav
five 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.
FPL
This algorithm uses track history data to extrapolate intruders to their expected
positions consistent with the time of display in the cockpit. Occasionally, aircraft
Direct-To
maneuvering will cause this algorithm to induce errors in the display. These
errors primarily affect relative bearing information and traffic target track vector
Proc
(it will lag); intruder distance and altitude will remain relatively accurate and
may be used to assist in "see and avoid." Some of the more common examples
Charts
of these errors follow:
Wpt Info
• When client or intruder aircraft maneuvers excessively or abruptly, the
tracking algorithm may report incorrect horizontal position until the
Map
maneuvering aircraft stabilizes.
• When a rapidly closing intruder is on a course that crosses the client aircraft
Traffic
course at a shallow angle (either overtaking or head on) and either aircraft
Terrain abruptly changes course within 0.25 NM, TIS may display the intruder on
the opposite side of the client than it actually is.
Weather
These are relatively rare occurrences and will be corrected in a few
radar scans once the course has stabilized.
Nearest
Music
Utilities
System
Messages
Symbols
Appendix
10-6
Index
Garmin GTN 725/750 Pilot's Guide 190-01007-03 Rev. B