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positions consistent with the time of display in the
cockpit. Occasionally, aircraft maneuvering will
cause this algorithm to induce errors in the TIS
display. These errors primarily affect relative bearing
information; 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 are as follows:
(1) When client or intruder aircraft maneuver
excessively or abruptly, the tracking algorithm
will report incorrect horizontal position until the
maneuvering aircraft stabilizes.
(2) When a rapidly closing intruder is on a
course that crosses the client at a shallow angle (either
overtaking or head on) and either aircraft abruptly
changes course within ¼ NM, TIS will 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.
(g) Heading/Course Reference. Not all TIS
aircraft installations will have onboard heading
reference information. In these installations, aircraft
course reference to the TIS display is provided by the
AIM 2/14/08
4-5-14 Surveillance Systems
Mode S radar. The radar only determines ground
track information and has no indication of the client
aircraft heading. In these installations, all intruder
bearing information is referenced to ground track and
does not account for wind correction. Additionally,
since ground-based radar will require several scans
to determine aircraft course following a course
change, a lag in TIS display orientation (intruder
aircraft bearing) will occur. As in (f) above, intruder
distance and altitude are still usable.
(h) Closely-Spaced Intruder Errors.
When operating more than 30 NM from the Mode S
sensor, TIS forces any intruder within 3/8 NM of the
TIS client to appear at the same horizontal position as
the client aircraft. Without this feature, TIS could
display intruders in a manner confusing to the pilot in
critical situations (e.g., a closely-spaced intruder that
is actually to the right of the client may appear on the
TIS display to the left). At longer distances from the
radar, TIS cannot accurately determine relative
bearing/distance information on intruder aircraft that
are in close proximity to the client.
Because TIS uses a ground-based, rotating radar for
surveillance information, the accuracy of TIS data is
dependent on the distance from the sensor (radar)
providing the service. This is much the same
phenomenon as experienced with ground-based
navigational aids, such as VOR or NDB. As distance
from the radar increases, the accuracy of surveillance
decreases. Since TIS does not inform the pilot of
distance from the Mode S radar, the pilot must assume
that any intruder appearing at the same position as the
client aircraft may actually be up to 3/8 NM away in
any direction. Consistent with the operation of TIS,
an alert on the display (regardless of distance from the
radar) should stimulate an outside visual scan,
intruder acquisition, and traffic avoidance based on
outside reference.
e. Reports of TIS Malfunctions
1. Users of TIS can render valuable assistance in
the early 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:
(a) By radio or telephone to the nearest Flight
Service Station (FSS) facility.
(b) 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.
4-5-7. Automatic Dependent
Surveillance-Broadcast (ADS-B) Services
a. Introduction
1. Automatic Dependent Surveillance-Broadcast
(ADS-B) is a surveillance technology being
deployed in selected areas of the NAS (see
FIG 4-5-7). ADS-B broadcasts a radio transmission
approximately once per second containing the
aircraft's position, velocity, identification, and other
information. ADS-B can also receive reports from
other suitably equipped aircraft within reception
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