Air traffic control :

                                  Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able.

                                                         The ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAMs (NOtices To AirMen). In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users (private, military, and commercial).