1: Traffic Collision Avoidance System. A computerised system in a modern airliner which utilizes radar, transponder data and in-system logic with the aim of providing collision avoidance if Air Traffic Controll fails to.
2: The alarm itself in the cockpit
1: The Aircraft was fitted with a state of the art TCAS
2: The pilots were alerted to the situation by the onboard alarm, audibly sounding off "TCAS ALERT; TCAS ALERT", Their quick response warded off disaster.