Plain English Meaning

An onboard system that watches for other aircraft using their transponder signals and warns the pilot if one is getting too close. If a collision is likely, it tells the pilot to climb or descend to stay clear.

Full Definition

An airborne collision avoidance system that interrogates the transponders of nearby aircraft, tracks their range, bearing, and altitude, and issues two levels of alert to the pilot: a Traffic Advisory (TA) indicating nearby traffic that may become a threat, and a Resolution Advisory (RA) directing a vertical maneuver (climb or descend) to avoid a collision. TCAS II is mandated for most -powered transport aircraft operating in U.S. .