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AIM 

6/17/21 

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

5. 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

7). The ADS

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 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

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. 

4. 

In general, operators flying at 18,000 feet and 

above (Class A airspace) are required to have 1090ES 
equipment. 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 regulations do 
not require it, operators equipped with ADS

B In will 

realize additional benefits from ADS

B broadcast 

4

5

14 

Surveillance Systems