Garmin AERA 660 Pilot's Manual page 169

TIS-A 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-A 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-A may display the intruder aircraft on the
incorrect side of the client aircraft.
These are rare occurrences and are typically resolved within a few radar sweeps once
the client/intruder aircraft course stabilizes.
Pilots using TIS-A can provide valuable assistance in the correction of malfunctions
by reporting observations of undesirable performance. Reports should identify the time
of observation, location, type and identity of the aircraft, and describe the condition
observed. Reports should also include the type of transponder and transponder
software version. Since TIS-A performance is monitored by maintenance personnel,
not ATC, malfunctions should be reported in the following ways:
• By telephone to the nearest Flight Service Station (FSS) facility
• By FAA Form 8000-7, Safety Improvement Report (postage-paid card can be obtained
at FAA FSSs, General Aviation District Offices, Flight Standards District Offices, and
General Aviation Fixed Base Operators)
190-02017-20 Rev. A Garmin aera 660 Pilot's Guide
Appendix F
153