In aviation, an air traffic service is a service which regulates and assists aircraft in real-time to ensure their safe operations. In particular, ATS is to:
prevent collisions between aircraft; provide advice of the safe and efficient conduct of flights;
conduct and maintain an orderly flow of air traffic;
notify concerned organizations of and assist in search and rescue operations.
The ATS further provides four services:
air traffic control services, which is to prevent collisions in controlled airspace by instructing pilots where to fly; From Wikipedia
