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AIM 

4/20/23 

(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 

¼

 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

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

Broadcast (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 information about the aircraft to ground stations for use by ATC and other ADS

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 

4

5

18 

Surveillance Systems