Traffic Alert and Collision Avoidance System
Traffic Alert and Collision Avoidance System (TCAS) systems introduce a new level of safety into air traffic control, by providing an information system that is separate from, but complimentary to, the conventional system based on directions from air traffic controllers to aircraft. Originally developed by the Federal Aviation Administration, and coordinated with international bodies, the technology is mature, and development and operation have passed to industry.
As a safety of navigation system autonomous of central control, it is similar to the automatic identification system used with watercraft.
The Traffic Alert and Collision Avoidance System (TCAS) is an airborne system developed by the FAA that operates independently from the ground-based Air Traffic Control (ATC) system. TCAS was designed to increase cockpit awareness of proximate aircraft and to serve as a "last line of defense" for the prevention of mid-air collisions.
TCAS I was developed to accommodate the general aviation (GA) community and the regional airlines. This system issues ‘Traffic Advisories’ (TAs) to assist pilots in visual acquisition of intruder aircraft. It will warn "TRAFFIC, TRAFFIC" but not any directions.
TCAS II is a more sophisticated system which provides the information of TCAS I, and also analyzes the projected flight path of approaching aircraft and issues ‘Resolution Advisories’ (RAs) to the pilot to resolve potential mid-air collisions. Such an advisory might tell one aircraft to climb and the other to dive.
TCAS is now under RTCA, Inc. "a private, not-for-profit corporation that develops consensus-based recommendations regarding communications, navigation, surveillance, and air traffic management (CNS/ATM) system issues." RTCA documents, however, are "deep web", not accessible withut paying fees.