11/3/22
AIM
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 (for example, 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 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
−
TIS operates at only those terminal Mode S radar sites
depicted in FIG 4
−
5
−
6. Though similar in some ways, TIS
is not related to TIS
−
B (Traffic Information Service
−
Broadcast).
4
−
5
−
7. Automatic Dependent
Surveillance
−
Broadcast (ADS
−
B) Services
a. Introduction.
1.
Automatic Dependent Surveillance
−
Broad-
cast (ADS
−
B) is a surveillance technology deployed
throughout the NAS (see FIG 4
−
5
−
8). The ADS
−
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 informa-
tion about the aircraft to ground stations for use by
ATC and other ADS
−
B services. This information is
transmitted at a rate of approximately once per
second. (See FIG 4
−
5
−
9 and FIG 4
−
5
−
10.)
2.
In the United States, ADS
−
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 MHz transponders
with integrated ADS
−
B functionality extend the
transponder message sets with additional ADS
−
B
information. This additional information is known
as an “extended squitter” message and is referred to
as 1090ES. ADS
−
B equipment operating on 978
MHz is known as the Universal Access Transceiver
(UAT).
3.
ADS
−
B avionics can have the ability to both
transmit and receive information. The transmission
of ADS
−
B information from an aircraft is known as
ADS
−
B Out. The receipt of ADS
−
B information by
an aircraft is known as ADS
−
B In. All aircraft
operating within the airspace defined in 14 CFR
§ 91.225 are required to transmit the information
defined in § 91.227 using ADS
−
B Out avionics.
Surveillance Systems
4
−
5
−
15