High Quality Content by WIKIPEDIA articles! A marker beacon is a particular type of low frequency radio beacon used in aviation, usually in conjunction with an instrument landing system, to give pilots a means to determine position along an established route to a destination such as a runway. From the 1930s until the 1950s, markers were used extensively along airways to provide an indication of an aircraft's specific position along the route, but from the 1960s they have become increasingly limited to ILS approach installations. They are now very gradually being phased out of service, especially in more developed parts of the world, as GPS and other technologies have made marker beacons increasingly obsolete.