Garmin GTN 625 Pilot's Manual page 184

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.
Xpdr Ctrl
TIS information is collected one radar scan prior to the scan during which
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
Wpt Info
of these errors follow:
Map
• When client or intruder aircraft maneuvers excessively or abruptly, the
tracking algorithm may report incorrect horizontal position until the
Traffic
maneuvering aircraft stabilizes.
• When a rapidly closing intruder is on a course that crosses the client aircraft
Terrain
course at a shallow angle (either overtaking or head on) and either aircraft
Weather abruptly changes course within 0.25 NM, TIS may display the intruder on
the opposite side of the client than it actually is.
Nearest
These are relatively rare occurrences and will be corrected in a few
radar scans once the course has stabilized.
Services/
Music
Utilities
System
Messages
Symbols
Appendix
Index
9-8
Garmin GTN 625/635/650 Pilot's Guide 190-01004-03 Rev. F