3
TIS Operation and Symbology
Section 1
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 intrud-
ers 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 will cause this algorithm to induce
errors in the 400/500 display. These errors primarily affect relative bearing information and traffic target
track vector (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 of these errors follow:
• When 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 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 display the intruder on the opposite side of the client than it actually is.
These are relatively rare occurrences and will be 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 postage-paid card designed for this
purpose. These cards may be obtained at
FAA FSSs, General Aviation District Offices,
Flight Standards District Offices, and General
Aviation Fixed Based Operations.
