Development and operation of the Traffic Alert and Collision Avoidance System (TCAS)

The authors describe the development of the Traffic Alert and Collision Avoidance System (TCAS), provide a description of the TCAS II system operation, offer results of operational evaluations conducted in cooperation with Piedmont, United, and Northwest Airlines, and outline the status and progress of the TCAS implementation. In recent years, the TCAS effort has focused on concepts that make use of the radar transponders carried by aircraft for ground air traffic control purposes. A transponder-based collision avoidance system can provide immediate protection against the vast population of aircraft already equipped with either the current Air Traffic Control Radar Beacon System (ATCRBS) transponder or the new Mode S transponder. The TCAS concept encompasses a range of capabilities, including TCAS I, which provides traffic advisories (bearing, range, and relative altitude) to assist the pilot in visually acquiring the threat aircraft; TCAS II, which provides traffic and resolution advisories (recommended escape maneuvers) in the vertical plane; and TCAS III, which provides traffic and resolution advisories in both the vertical and horizontal planes