(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)
above).
(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.
NOTE-
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.

4-5-12

(b) The intruder ground track diverges to the
right of the client aircraft, indicated by the small
arrow.
(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.
NOTE-
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"s
responsibility to "see and avoid" other aircraft (see
Paragraph 5-5-8, See and Avoid). TIS must not be
used 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. Avoidance
maneuvers are neither provided 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
indicated in FIG 4-5-4. TIS users must be alert to

Surveillance Systems