The NAS spans the country, extends into the oceans, and interfaces with neighboring air traffic control systems for international flights. The NAS relies on approximately 30,000 FAA employees to provide air traffic control, flight service, security, and field maintenance services. More than 616,000 active pilots operating over 280,000 commercial, regional, general aviation and military aircraft use the NAS. .

             On March 11, 1999, the FAA released the NAS Architecture Version 4.0 to the public. Key influences on the architecture include the 1996 White House Commission on Aviation Safety and Security, which recommended that the FAA accelerate modernization of the NAS, and the 1997 National Civil Aviation Review Commission, which recommended funding and performance management methods for implementing NAS modernization. It describes the agency¡s modernization strategy from 1998 through 2015. Based on the Free Flight operational concept, Version 4.0 contains capabilities, technologies, and systems to enhance the safety of the aviation system and provide users and service providers with more efficient services. Free Flight centers on allowing pilots, whenever practical, to choose the optimum flight profile. This concept of operations is expected to decrease user costs, improve airspace flexibility, and remove flight restrictions. .

             The NAS Architecture is divided into three modernization phases and its implementation is being synchronized with the International Civil Aviation Organization to ensure interoperability and global integration. .

             „h Phase 1 (1998-2002) focuses on sustaining essential air traffic control services and delivering early user benefits. Free Flight Phase 1 will be implemented. Controller computer workstations will begin major upgrades. Satellite-based navigation systems will be deployed, and air-to-air surveillance will be introduced. The ¡§Year 2000¡ computer problem will hopefully be fixed.