VOR which is co-located with a DME is usually a component of a TACAN. Prior to the advent of GNSS, Celestial Navigation was also used by trained navigators on military bombers and transport aircraft in the event of all electronic navigational aids being turned off in time of war. Originally navigators used an astrodome and regular sextant but the more streamlined periscopic sextant was used from the 1940s to the 1990s. From the 1970s airliners used inertial navigation systems, especially on inter-continental routes, until the shooting down of Korean Air Lines Flight 007 in 1983 prompted the US government to make GPS available for civilian use. Finally, an aircraft may be supervised from the ground using surveillance information from e.g. radar or multilateration. ATC can then feed back information to the pilot to help establish position, or can actually tell the pilot the position of the aircraft, depending on the level of ATC service the pilot is receiving. The use of GNSS in aircraft is becoming increasingly common. GNSS provides very precise aircraft position, altitude, heading and ground speed information. GNSS makes navigation precision once reserved to large RNAV-equipped aircraft available to the GA pilot. Recently, many airports include GNSS instrument approaches. GNSS approaches consist of either overlays to existing precision and non-precision approaches or stand-alone GNSS approaches. Approaches having the lowest decision heights generally require that GNSS be augmented by a second system—e.g., the FAA's Wide Area Augmentation System (WAAS). Flight navigator Civilian flight navigators (a mostly redundant aircrew position, also called 'air navigator' or 'flight navigator'), were employed on older aircraft, typically between the late-1910s and the 1970s. The crew member, occasionally two navigation crew members for some flights, was responsible for the trip navigation, including its dead reckoning and celestial navigation. This was especially essential when trips were flown over oceans or other large bodies of water, where radio navigation aids were not originally available. (satellite coverage is now provided worldwide). As sophisticated electronic and GNSS systems came online, the navigator's position was discontinued and its function was assumed by dual-licensed pilot-navigators, and still later by the flight's primary pilots (Captain and First Officer), resulting in a downsizing in the number of aircrew positions for commercial flights. As the installation of electronic navigation systems into the Captain's and FO's instrument panels was relatively straight forward, the navigator's position in commercial aviation (but not necessarily military aviation) became