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Surveillance Systems

(d) No Traffic. No intruders meet proximate

or alert criteria. This condition may exist when the

TIS system is fully functional or may indicate

“coasting” between 12 and 59 seconds old (see (c)


(e) TIS Unavailable. The pilot has re-

quested TIS, but no ground system is available. This

condition will also be displayed when TIS uplinks are

missing for 60 seconds or more.

(f) TIS Disabled. The pilot has not requested

TIS or has disconnected from TIS.

(g) Good−bye. The client aircraft has flown

outside of TIS coverage.


Depending on the avionics manufacturer implementation,

it is possible that some of these messages will not be directly

available to the pilot.

5. Depending on avionics system design, TIS

may be presented to the pilot in a variety of different

displays, including text and/or graphics. Voice

annunciation may also be used, either alone or in

combination with a visual display. FIG 4−5−6,

Traffic Information Service (TIS), Avionics Block

Diagram, shows an example of a TIS display using

symbology similar to the Traffic Alert and Collision

Avoidance System (TCAS) installed on most

passenger air carrier/commuter aircraft in the U.S.

The small symbol in the center represents the client

aircraft and the display is oriented “track up,” with the

12 o’clock position at the top. The range rings

indicate 2 and 5 NM. Each intruder is depicted by a

symbol positioned at the approximate relative

bearing and range from the client aircraft. The

circular symbol near the center indicates an “alert”

intruder and the diamond symbols indicate “proxi-

mate” intruders.

6. The inset in the lower right corner of

FIG 4−5−6, Traffic Information Service (TIS),

Avionics Block Diagram,


shows a possible TIS data

block display. The following information is con-

tained in this data block:

(a) The intruder, located approximately

four o’clock, three miles, is a “proximate” aircraft

and currently not a collision threat to the client

aircraft. This is indicated by the diamond symbol

used in this example.

(b) The intruder ground track diverges to the

right of the client aircraft, indicated by the small


(c) The intruder altitude is 700 feet less than

or below the client aircraft, indicated by the “−07”

located under the symbol.

(d) The intruder is descending >500 fpm,

indicated by the downward arrow next to the “−07”

relative altitude information. The absence of this

arrow when an altitude tag is present indicates level

flight or a climb/descent rate less than 500 fpm.


If the intruder did not have an operating altitude encoder

(Mode C), the altitude and altitude trend “tags” would

have been omitted.

d. Limitations.

1. TIS is NOT intended to be used as a collision

avoidance system and does not relieve the pilot

responsibility to “see and avoid” other aircraft (see

paragraph 5−5−8, See and Avoid). TIS must not be for

avoidance maneuvers during IMC or other times

when there is no visual contact with the intruder

aircraft. TIS is intended only to assist in visual

acquisition of other aircraft in VMC. No recom-

mended avoidance maneuvers are provided for,

nor authorized, as a direct result of a TIS intruder

display or TIS alert.

2. While TIS is a useful aid to visual traffic

avoidance, it has some system limitations that must

be fully understood to ensure proper use. Many of

these limitations are inherent in secondary radar

surveillance. In other words, the information

provided by TIS will be no better than that provided

to ATC. Other limitations and anomalies are

associated with the TIS predictive algorithm.

(a) Intruder Display Limitations. TIS will

only display aircraft with operating transponders

installed. TIS relies on surveillance of the Mode S

radar, which is a “secondary surveillance” radar

similar to the ATCRBS described in para-

graph 4−5−2.

(b) TIS Client Altitude Reporting Require-

ment. Altitude reporting is required by the TIS client

aircraft in order to receive TIS. If the altitude encoder

is inoperative or disabled, TIS will be unavailable, as

TIS requests will not be honored by the ground

system. As such, TIS requires altitude reporting to

determine the Proximity Coverage Volume as