TCAS II is a system used for detecting and tracking aircraft in the vicinity of your own aircraft. By interrogating their transponders it analyzes the replies to determine range, bearing, and if reporting altitude, the relative altitude of the intruder.
ATC procedures and the “see and avoid concept” will continue to be the primary means of ensuring aircraft separation. However, if communication is lost with ATC, TCAS II adds a significant backup for collision avoidance.
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 areas 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.