TRAFFIC INFORMATION SERVICE (TIS)
Traffic Information Service (TIS) provides information to the cockpit via data
link, that is similar to VFR radar traffic advisories normally received over
voice radio. Among the first
FAA-provided data services, TIS is intended to improve the safety and
efficiency of "see and avoid" flight through an automatic display
that informs the pilot of nearby traffic and potential conflict situations.
This traffic display is intended to assist the pilot in visual
acquisition of these aircraft. TIS
employs an enhanced capability of the terminal Mode S radar system, which
contains the surveillance data, as well as the data link required to
“uplink” this information to suitably-equipped aircraft (known as a TIS
“client”). TIS provides
estimated position, altitude, altitude trend, and ground track information for
up to 8 intruder aircraft within 7 NM horizontally, +3,500 and –3,000 feet
vertically of the client aircraft (see Figure 1-2-4). The range of a target
reported at a distance greater than 7 NM only indicates that this target will
be a threat within 34 seconds and does not
display an precise distance. TIS will alert the pilot to aircraft (under
surveillance of the Mode S radar) that are estimated to be within 34 seconds
of potential collision, regardless of distance of altitude. TIS surveillance
data is derived from the same radar used by ATC; this data is uplinked to the
client aircraft on each radar scan (nominally every 5 seconds).
Proximity Coverage Volume
In order to use TIS, the client and any intruder aircraft must be
equipped with the appropriate cockpit equipment and fly within the radar
coverage of a Mode S radar capable of providing TIS.
Typically, this will be within 55 NM of the sites depicted in Figure
1-2-5. ATC communication is not a
requirement to receive TIS, although it may be required by the particular
airspace or flight operations in which TIS is being used.
2. The cockpit equipment
functionality required by a TIS client aircraft to receive the service
consists of the following (refer to Figure 1-2-6):
Mode S data link transponder with altitude encoder.
Data link applications processor with TIS software installed.
Optional equipment includes a digital heading source to correct display
errors caused by "crab angle" and turning maneuvers.
Some of the above functions will likely be combined into single pieces
of avionics, such as (a) and (b).
To be visible to the TIS client, the intruder aircraft must, at a
minimum, have an operating transponder (Mode A, C or S).
All altitude information provided by TIS from intruder aircraft is
derived from Mode C reports, if appropriately equipped.
TIS will initially be provided by the terminal Mode S systems that are
paired with ASR-9 digital primary radars.
These systems are in locations with the greatest traffic densities,
thus will provide the greatest initial benefit.
The remaining terminal Mode S sensors, which are paired with ASR-7 or
ASR-8 analog primary radars, will provide TIS pending modification or
relocation of these sites. See
Figure 1-2-5 for site locations. There
is no mechanism in place, such as NOTAMs, to provide status update on
individual radar sites since TIS is a non-essential, supplemental information
FAA also operates en route Mode S radars (not illustrated) that rotate once
every 12 seconds. These sites
will require additional development of TIS before any possible implementation.
There are no plans to implement TIS in the en route Mode S radars at
the present time.
provides ground-based surveillance information over the Mode S data link to
properly-equipped client aircraft to aid in visual acquisition of proximate
air traffic. The actual avionics
capability of each installation will vary and the supplemental handbook
material must be consulted prior to using TIS.
A maximum of eight (8) intruder aircraft may be displayed; if more than
eight aircraft match intruder parameters, the eight “most significant”
intruders are uplinked. These
“most significant” intruders are usually the ones in closest proximity
and/or the greatest threat to the TIS client.
TIS, through the Mode S ground sensor, provides the following data on
each intruder aircraft:
Relative bearing information in 6-degree increments.
Relative range information in 1/8 NM to 1 NM increments (depending
Relative altitude in 100-foot increments (within 1,000 feet) or
500-foot increments (from 1,000-3,500 feet) if the intruder aircraft has
operating altitude reporting capability.
Estimated intruder ground track in 45-degree increments.
Altitude trend data (level within 500 fpm or climbing/descending
>500 fpm) if the intruder aircraft has operating altitude reporting
Intruder priority as either an “traffic advisory” or
When flying from surveillance coverage of one Mode S sensor to
another, the transfer of TIS is an automatic function of the avionics system
and requires no action from the pilot.
There are a variety of status messages that are provided by either
the airborne system or ground equipment to alert the pilot of high priority
intruders and data link system status. These messages include the following:
Alert: Identifies a
potential collision hazard within 34 seconds.
This alert may be visual and/or audible, such as a flashing display
symbol or a headset tone. A target is a threat if the time to the closest
approach in vertical and horizontal coordinates is less that 30 seconds and
the closest approach is expected to be within 500 feet vertically and 0.5
nautical miles laterally.
TIS Traffic: TIS
traffic data is displayed.
Coasting: The TIS
display is more than 6 seconds old. This
indicates a missing uplink from the ground system.
When the TIS display information is more than 12 seconds old, the “No
Traffic” status will be indicated.
(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).
TIS Unavailable: The
pilot has requested TIS, but no ground system is available.
This condition will also be displayed when TIS uplinks are missing for
60 seconds or more.
TIS Disabled: The
pilot has not requested TIS or has disconnected from TIS.
The client aircraft has flown
outside of TIS coverage.
on the avionics manufacturer implementation, it is possible that some of these
messages will not be directly available to the pilot.
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. Figure
1-2-6 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 “proximate” intruders.
The inset in the lower right corner of Figure 1-2-6 shows a possible
TIS data block display. The
following information is contained in this data block:
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.
The intruder ground track diverges to the right of that of the
client aircraft, indicated by the small arrow.
The intruder altitude is 700 feet less than or below the client
aircraft, indicated by the “-07” located under the symbol.
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.
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 section 5-5-8
of this publication). TIS shall
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
recommended 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.
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 paragraph 1-2-2 of
TIS Client Altitude Reporting Requirement:
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 Figure
1-2-4. TIS users must be alert to altitude encoder malfunctions, as TIS has no
mechanism to determine if client altitude reporting is correct.
A failure of this nature will cause erroneous and possibly
unpredictable TIS operation. If
this malfunction is suspected, confirmation of altitude reporting with ATC is
Intruder Altitude Reporting: Intruders
without altitude reporting capability will be displayed without the
accompanying altitude tag. Additionally,
non-altitude reporting intruders are assumed to be at the same altitude as the
TIS client for alert computations. This
helps to ensure that the pilot will be alerted to all traffic under radar
coverage, but the actual altitude difference may be substantial.
Therefore, visual acquisition may be difficult in this instance.
(d) Coverage Limitations:
TIS is provided by ground-based, secondary surveillance radar, it is subject
to all limitations of that radar. If
an aircraft is not detected by the radar, it can not be displayed on TIS.
Examples of these limitations are as follows:
will typically be provided within 55 NM of the radars depicted in Figure
1-2-5. This maximum range can
vary by radar site and is always subject to “line of sight” limitations;
the radar and data link signals will be blocked by obstructions, terrain, and
curvature of the earth.
TIS will be unavailable at low altitudes in many areas of the country,
particularly in mountainous regions. Also,
when flying near the “floor” of radar coverage in a particular area,
intruders below the client aircraft may not be detected by TIS.
(3)TIS will be temporarily
disrupted when flying directly over the radar site providing coverage if no
adjacent site assumes the service. A ground-based radar, like a VOR or
NDB, has a zenith cone, sometimes referred to as the cone of confusion
or cone of silence. This is the
area of ambiguity directly above the station where bearing information is
unreliable. The zenith cone
setting for TIS is 34 degrees: Any
aircraft above that angle with respect to the radar horizon will lose TIS
coverage from that radar until it is below this 34 degree angle.
The aircraft may not actually lose service in areas of multiple radar
coverage since an adjacent radar will provide TIS.
If no other TIS-capable radar is available, the "Goodbye"
message will be received and TIS terminated until coverage is resumed.
Intermittent Operations: TIS
operation may be intermittent during turns or other maneuvering, particularly
if the transponder system does not include antenna diversity (antenna mounted
on the top and bottom of the aircraft). As
in (d) above, TIS is dependent on two-way, “line of sight” communications
between the aircraft and the Mode S radar.
Whenever the structure of the client aircraft comes between the
transponder antenna (usually located on the underside of the aircraft) and the
ground-based radar antenna, the signal may be temporarily interrupted.
TIS Predictive Algorithm: TIS
information is collected one radar scan prior to the scan during which the
uplink occurs. Therefore, the
surveillance information is approximately 5 seconds old.
In order to present the intruders in a “real time” position, TIS
uses a “predictive algorithm” in its tracking software.
This algorithm uses track history data to extrapolate intruders to
their expected positions consistent with the time of display in the cockpit.
Occasionally, aircraft maneuvering will cause this algorithm to induce
errors in the TIS display. These
errors primarily affect relative bearing information; intruder distance and
altitude will remain relatively accurate and may be used to assist in “see
and avoid.” Some of the more
common examples of these errors are as follows:
When client or intruder aircraft maneuver excessively or abruptly,
the tracking algorithm will report incorrect horizontal position until the
maneuvering aircraft stabilizes.
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.
are relatively rare occurrences and will be corrected in a few radar scans
once the course has stabilized.
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.
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.
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
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 in the following ways:
By telephone to the nearest Flight Service Station (FSS) facility.
By FAA Form 8000-7, Safety Improvement
Report, a postage-paid card designed for this purpose.
These cards may be obtained at FAA FSSs, General Aviation District
Offices, Flight Standards District Offices, and General Aviation Fixed Based
TRAFFIC INFORMATION SERVICE (TIS)
provides proximity warning only, to assist the pilot in the visual acquisition
of intruder aircraft. No
recommended avoidance maneuvers are provided nor authorized as a direct result
of a TIS intruder display or TIS alert. It
is intended for use by aircraft in which TCAS is not required.
TIS does not alter or diminish the pilot’s basic authority and
responsibility to ensure safe flight. Since
TIS does not respond to aircraft which are not transponder equipped, aircraft
with a transponder failure, or aircraft out of radar coverage, TIS alone does
not ensure safe separation in every case.
c. At this time, no air
traffic service nor handling is predicated on the availability of TIS
equipment in the aircraft.