ED-143 sets forth Minimum Operational Performance Standards (MOPS) for Traffic Alert and Collision Avoidance System II (TCAS II) equipment. TCAS II is intended to improve air safety by acting as a last-resort method of preventing mid-air collisions or near collisions between aircraft. By utilizing Secondary Surveillance Radar (SSR) technology, TCAS II equipment operates independently of ground-based aids and air traffic control (ATC). Aircraft equipped with TCAS II have the ability to interrogate airborne transponders to monitor range, bearing, and reported altitude of other aircraft in the vicinity and assess the risk of collision. Non-transponding aircraft are not detected.