vertical distances shown in  Figure 11-131 , an audible TA is  announced. The pilot must decide whether to take action and  what action to take. TCAS II equipped aircraft use continuous  reply information to analyze the speed and trajectory of target  aircraft in close proximity. If a collision is calculated to be  imminent, an RA is issued.  TCAS target aircraft are displayed on a screen on the  flight deck. Different colors and shapes are used to depict  approaching aircraft depending on the imminent threat level.  Since RAs are currently limited to vertical evasive maneuvers,  some stand-alone TCAS displays are electronic vertical speed  indicators. Most aircraft use some version of an electronic HSI  on a navigational screen or page to display TCAS information.  [Figure 11-132]  A multifunction display may depict  TCAS and weather radar information on the same screen.  [Figure 11-133]  A TCAS control panel  [Figure 11-134]  and  computer are required to work with a compatible transponder  and its antenna(s). Interface with EFIS or other previously  installed or selected display(s) is also required. TCAS may be referred to as airborne collision avoidance  system (ACAS), which is the international name for the same  system. TCAS II with the latest revisions is known as Version  7. The accuracy and reliability of this TCAS information is  such that pilots are required to follow a TCAS RA over an  ATC command.  Collision avoidance is a significant part of the FAA’s  NextGen plan for transforming the National Airspace  System (NAS). Increasing the number of aircraft using the  same quantity of airspace and ground facilities requires the  implementation of new technologies to maintain a high level  of performance and safety. The successful proliferation of  global navigation satellite systems (GNSS), such as GPS,  has led to the development of a collision avoidance system  known as automatic dependent surveillance broadcast  (ADS-B). ADS-B is an integral part of NextGen program.  The implementation of its ground and airborne infrastructure  is currently underway. ADS-B is active in parts of the United  States and around the world.  [Figure 11-135] ADS-B is considered in two segments: ADS-B OUT  and ADS-B IN. ADS-B OUT combines the positioning  information available from a GPS receiver with on-board  Figure 11-134.  This control panel from a Boeing 767 controls the  transponder for ATC use and TCAS.  Figure 11-133.  TCAS information displayed on a multifunction  display. An open diamond indicates a target; a solid diamond  represents a target that is within 6 nautical miles of 1,2000 feet  vertically. A yellow circle represents a target that generates a TA  (25-48 seconds before contact). A red square indicates a target  that generates an RA in TCAS II (contact within 35 seconds). A (+)  indicates the target aircraft is above and a (-) indicates it is below.  The arrows show if the target is climbing or descending.  Figure 11-132.  TCAS information displayed on an electronic vertical  speed indicator.  ADS-B 1 5 5 2 1 2 4 197 GS 356 TAS386 195° 17 HDG MAG TRAFFIC +30 +13 +02 −12 TCAS/ATC ABOVE ABS BELOW REL ABOVE ABS BELOW FAIL REL N N XPDR STBY TA TEST TA/RA 0 0 0 0 L R 11-60