Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and in the air through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The Primary Purpose of ATC worldwide Is to prevent collisions, organize and expedite the flow of air traffic, and provide information and other support for pilots.
Air traffic controllers monitor the location of aircraft in their assigned airspace by radar and communicate with the pilots by radio. To prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of space around it at all times. In many countries, ATC provides services to all private, military, and commercial aircraft operating within its airspace.
Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to obey, or advisories (known as flight information). The pilot in command is the final authority for the safe operation of the aircraft and may in an emergency, deviate from ATC instructions to the extent required to maintain safe operation of their aircraft.