Figure 5-48.  Aircraft equipped with Automatic Dependent Surveillance—Broadcast (ADS-B) continuously broadcast their identification,  altitude, direction, and vertical trend. The transmitted signal carries significant information for other aircraft and ground stations alike.  Other ADS-equipped aircraft receive this information and process it in a variety of ways. It is possible that in a saturated environment  (assuming all aircraft are ADS equipped), the systems can project tracks for their respective aircraft and retransmit to other aircraft  their projected tracks, thereby enhancing collision avoidance. At one time, there was an Automatic Dependent Surveillance—Addressed  (ADS-A) and that is explained in the Pilot’s Handbook of Aeronautical Knowledge. trend, and ground track information for up to several aircraft  simultaneously within about 7 NM horizontally, 3,500 feet  above and 3,500 feet below the aircraft.  [Figure 5-52]  This  data can be displayed on a variety of MFDs.  [Figure 5-53] Figure 5-54 displays the pictorial concept of the traffic  information system. Noteworthy is the requirement to have  Mode S and that the ground air traffic station processes the  Mode S signal. Traffic alert systems receive transponder information from  nearby aircraft to help determine their relative position to the  equipped aircraft. They provide three-dimensional location  of other aircraft  [Figures 5-55, 5-56,  and  5-57]  and are cost  effective alternatives to TCAS equipage for smaller aircraft.  There are two levels of TCAS systems. TCAS I was developed  to accommodate the general aviation (GA) community and  the regional airlines. This system issues traffic advisories  (TAs) to assist pilots in visual acquisition of intruder aircraft.  TCAS I provides approximate bearing and relative altitude  of aircraft with a selectable range. It provides the pilot with  TA alerting him or her to potentially conflicting traffic. The  pilot then visually acquires the traffic and takes appropriate  action for collision avoidance.  The TCAS is an airborne system developed by the FAA that  operates independently from the ground-based ATC system.  TCAS was designed to increase flight deck awareness of  proximate aircraft and to serve as a “last line of defense” for  the prevention of mid-air collisions.  Traffic Avoidance Systems Traffic Alert and Collision Avoidance System (TCAS)  Traffic Alert Systems  5-30