APA

United States, . (19). Maintenance of NAS en route stage A air traffic control system. [Washington, D.C: .

Chicago

United States, . 19. Maintenance of NAS en route stage A air traffic control system. [Washington, D.C: .

Harvard

United States, . (19). Maintenance of NAS en route stage A air traffic control system. [Washington, D.C: .

MLA

United States, . Maintenance of NAS en route stage A air traffic control system. [Washington, D.C: . 19.