Most passenger aircraft today are fitted with TCAS, a system that warns pilots if they come too close to other traffic.
As the name suggests, TCAS is intended to prevent mid-air collisions. Functioning independently of air traffic control and on-board navigation systems, it provides two levels of alert: a “traffic advisory” (TA) and a “resolution advisory” (RA).
These are activated according to the time left before a potential collision. A TA notifies the crew that other traffic is in the area, but the responsibility for maintaining its separation remains with air traffic control. An RA warns of an impending conflict – a flight-critical situation – and issues orders to climb or descend, which the crew have to follow. As such, an RA overrules instructions from air traffic control. In addition, TCAS provides pilots with an overall picture of other traffic in the area on a cockpit display.
