TCAS II is a system used for detecting and tracking aircraft in the area of an aircraft. TCAS interrogates transponders in other aircraft and analyzes the replies to determine range, bearing, and relative altitude (if reporting) of the intruder aircraft. When the TCAS II processor determines that a potential collision hazard exists, it will issue visual and audio advisories to the pilot/copilot for appropriate vertical avoidance maneuvers. TCAS is not able to detect aircraft without an operating ATCRBS transponder (operating in Mode A and C) or a Mode S transponder.
TCAS II utilizes two types of cockpit displays, Resolution Advisory (RA) and Traffic Advisory (TA) display. The RA is incorporated into the vertical speed indicator (VSI). With illuminating red and green arcs around the dial, the VSI displays the required rate, or limitation of climb or descent, to avoid a collision. The TA display shows the intruding aircraftâ€s relative position and altitude with a trend arrow to indicate if it is climbing or descending greater than 500 feet per minute. The TA display may be presented on compatible weather radar indicator or MFD, dedicated TCAS display or a TA/VSI display. The TA display uses symbols and colors to identify the relative threat of each intruder. Supplementing the displays, TCAS II provides appropriate synthesized voice announcements.