AIM 8/15/19  2. The cockpit equipment functionality required by a TIS client aircraft to receive the service consists of the following (refer to FIG 4 − 5 − 6): (a) Mode S data link transponder with altitude encoder. (b) Data link applications processor with TIS software installed. (c) Control − display unit. (d) Optional equipment includes a digital heading source to correct display errors caused by “crab angle” and turning maneuvers. NOTE − Some of the above functions will likely be combined into single pieces of avionics, such as (a) and (b). 3. 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. 4. 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 FIG 4 − 5 − 5, Terminal Mode S Radar Sites, for site locations. There is no mechanism in place, such as NOTAMs, to provide status update on individual radar sites since TIS is a nonessential, supplemental information service. The 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. c. Capabilities. 1. TIS 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. 2. TIS, through the Mode S ground sensor, provides the following data on each intruder aircraft: (a) Relative bearing information in 6 − degree increments. (b) Relative range information in 1/8 NM to 1 NM increments (depending on range). (c) 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. (d) Estimated intruder ground track in 45 − degree increments. (e) Altitude trend data (level within 500 fpm or climbing/descending >500 fpm) if the intruder aircraft has operating altitude reporting capability. (f) Intruder priority as either an “traffic advisory” or “proximate” intruder. 3. 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. 4. 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: (a) 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 coordi- nates is less than 30 seconds and the closest approach is expected to be within 500 feet vertically and 0.5 nautical miles laterally. (b) TIS Traffic. TIS traffic data is displayed. (c) 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. 4 − 5 − 11 Surveillance Systems