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AIM

10/12/17

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 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).