Aeronautical Information Manual (AIM), page 256

Index   255 -- Page 256 -- 257

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 by radio or telephone to the
nearest Flight Service Station (FSS) facility.

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 4-5-7). 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 4-5-8 and FIG 4-5-9.)

2. In the United States, ADS-B equipped
aircraft exchange information is on one of two
frequencies: 978 or 1090 MHz. The 1090 MHz
frequency is 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 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. On January 1,
2020, all aircraft operating within the airspace
defined in 14 CFR Part 91 § 91.225 will be required
to transmit the information defined in § 91.227
using ADS-B Out avionics.

4. In general, operators flying at 18,000 feet and
above will require equipment which uses 1090 ES.
Those that do not fly above 18,000 may use either
UAT or 1090ES equipment. (Refer to 14 CFR 91.225
and 91.227.) While the regulation will not require it,
operators equipped with ADS-B In will realize
additional benefits from ADS-B broadcast services:
Traffic Information Service – Broadcast (TIS-B)
(Paragraph 4-5-8) and Flight Information Service -
Broadcast (FIS-B) (Paragraph 4-5-9).

4-5-14 Surveillance Systems

Page 256 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   255 -- Page 256 -- 257