Airborne Collision Avoidance System

Airborne Collision Avoidance System (ACAS) is an ICAO (International Civil Aviation Organization) standard specified in ICAO Annex 10 Vol IV which provides pilots with a system independent of air traffic control to detect the presence of other aircraft which may present a threat of collision. Where the risk of collision is imminent, the system provides an indication of a manoeuvre that will reduce the risk of collision.
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The Traffic alert and Collision Avoidance System (or TCAS) is a computerised avionics device which is designed to reduce the danger of mid-air collisions between aircraft. It monitors the airspace around an aircraft, independent of air traffic control, and warns pilots of the presence of other aircraft which may present a threat of mid-air collision (MAC). It is an implementation of the Airborne Collision Avoidance System mandated by International Civil Aviation Organization to be fitted to all aircraft over 5700 kg or authorised to carry more than 19 passengers.
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