Positioning is one of the most important tasks in navigation technics. Each navigation task is grounded on positioning method. Successful movement depends on accuracy of an aircraft coordinate detection. The flight safety depends on availability and accuracy of positioning methods. Currently Global Navigation Satellite System (GNSS) provides a very accurate data about global position in comparison with other technics. GNSS is represented by GPS, GLONASS and GALILEO. Each airspace user has to use GNSS equipment for positioning purposes. But sometimes in several locations the accuracy of positioning may be not enough to guarantee the required level of flight safety. In this case we can use other positioning technics such as inertial positioning, hyperbolic navigation (eLORAN) or positioning by signals from radio beacons (NDB, DME, VOR, DVOR and e.t.).
In the sphere of aviation the most popular (by accuracy) is positioning by distance measurement equipment (or DME/DME). Nowadays the algorithms of Flight Management System have to use just one pair of DME beacons to detect position of aircraft. In this case the selection of the best pair of DME that is available in this part of airspace and has an optimal geometry of location has a crucial role. Accuracy of this positioning technique depends on the correct choice of ground DME stations.