An internationally standardized navigation system which allows an aircraft to measure its distance from a selected ground-based beacon. Such beacons are used throughout the world by all airliners, most of the military aircraft of the West, and a large number of general-aviation aircraft. The range of service is line of sight up to 300 mi (480 km), and system accuracy is usually 0.1 mi (0.16 km), but precision equipment, intended for use during landing, has accuracy of 20 ft (7 m).