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A microwave landing system (MLS) is a precision landing system originally intended to replace or supplement instrument landing systems (ILS). MLS has a number of operational advantages when compared to ILS, for instance, including a wide selection of channels to avoid interference with other nearby airports, excellent performance in all weather conditions, less influence of the orography in the quality of the signal, and more flexible range of vertical and horizontal descent angles, which in principle would allow for efficient descents. The system may be divided into five functions: approach azimuth, back azimuth, approach elevation, range and data communications.
MLS systems became operational in the 1990s. However, it has not been used much. This is due to two main reasons: first, the ILS has evolved and it is now more robust; second, and more important, GNSS systems allowed the expectation of the same level of positioning detail with no equipment needed at the airport. However, the GNSS navigation is still not a reality and therefore, and MLS continues to be of some interest in Europe.