ABSTRACT
The primary function of an air traffic control (ATC) system is to keep aircraft participating in the system separated from one another. The level of ATC services provided is usually based on each nation's priorities, technical abilities, weather conditions, and traffic complexity. All aircraft operations require an ATC clearance. Airspace with little or no potential traffic conflicts requires little in the way of sophisticated ATC systems. Every International Civil Aviation Organization (ICAO) signatory nation agrees to provide ATC services to all aircraft operating within its boundaries and agrees to accept that their pilots abide by other national ATC systems when operating within foreign countries. ICAO has just recently affirmed its preference for global navigation satellite system (GNSS) as the future primary international navigation standard. GNSSs have just recently been adopted as the future navigation standard by ICAO. Nonradar separation depends on accurate position determination and the transmittal of that information to the controller.
