TCAS II (Traffic alert and Collision Avoidance System II) in the United States and ACAS II (Airborne Collision Avoidance System II) Internationally. ACAS is currently required in European countries and will be required in the United States January 2021. The TCAS II is a system used for detecting and tracking aircraft in the vicinity of your own aircraft.The TPU-67A is the processor and configuration module for the TCAS II system working with lower and upper ANT-67A Antennas. By interrogating their transponders it analyzes the replies to determine range, bearing and if reporting altitude, the relative altitude of the intruder. Should the TCAS II processor determine that a possible collision hazard exists, it issues visual and audio advisories to the crew for appropriate vertical avoidance maneuvers. TCAS II is unable to detect any intruding aircraft without an operating ATCRBS transponder operating in Mode A and C or a Mode S transponder.

There are two types of cockpit displays for TCAS II, the Resolution Advisory (RA) display and the Traffic Advisory (TA) display. The RA display is incorporated into the vertical speed indicator (VSI) by illuminating red and green arcs around the dial it displays the required rate, or limitation of climb or descent, to avoid a possible collision. The TA display shows the intruding aircraft’s relative position and altitude with a trend arrow to indicate if it is climbing or descending at greater than 500 feet per minute. This TA display may be provided on the weather radar indicator, on a dedicated TCAS display or a TA/VSI display. The TA display identifies the relative threat of each intruder by using various symbols and colors. Complementing the displays, TCAS II provides appropriate synthesized voice announcements.