AIM 

4/20/23

 

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Surveillance Systems

(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 

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 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 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

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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

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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 (for
example, a closely

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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

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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

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based navigational aids, such as a VOR. 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 by radio or telephone to the nearest Flight Service Station (FSS)
facility.

NOTE

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TIS operates at only those terminal Mode S radar sites depicted in FIG 4

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5

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6. Though similar in some ways, TIS is not

related to TIS

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B (Traffic Information Service

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Broadcast).

4

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5

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7. Automatic Dependent Surveillance

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Broadcast (ADS

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B) Services

a. Introduction.

1.

Automatic Dependent Surveillance

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Broadcast (ADS

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B) is a surveillance technology deployed

throughout the NAS (see FIG 4

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5

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8). The ADS

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B system is composed of aircraft avionics and a ground

infrastructure. Onboard avionics determine the position of the aircraft by using the GNSS and transmit its
position along with additional information about the aircraft to ground stations for use by ATC and other ADS

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B

services. This information is transmitted at a rate of approximately once per second. (See FIG 4

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5

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9 and

FIG 4

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5

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10.)

2.

In the United States, ADS

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B equipped aircraft exchange information on one of two frequencies: 978 or

1090 MHz. The 1090 MHz frequency is also associated with Mode A, C, and S transponder operations. 1090