microwave landing system
[′mī·krə‚wāv ′land·iŋ ‚sis·təm] (navigation)
A system of ground equipment which generates guidance beams at microwave frequencies for guiding aircraft to landings; it is intended to replace the present lower-frequency instrument landing system. Abbreviated MLS.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
microwave landing system (MLS)
An instrument landing system operating in the microwave spectrum (5.0–5.25 GHz/15.4–15.7 GHz) that provides precision guidance in azimuth, elevation, and distance measurement to aircraft having compatible airborne equipment. There is no requirement of a localizer and a glide-slope as in an ILS (instrument landing system). An MLS allows approaches anywhere within its horizontal and vertical fan-shaped coverage area. It guides over a +/− 40° sector for landing and overshooting. It is useful for helicopters, short takeoff and landing (STOL) aircraft, and fixed-wing aircraft. The standard configuration of MLS ground equipment includes an azimuth station that provides an approach and back azimuth, an elevation station to provide an approach elevation, and precision distance-measuring equipment to indicate a continuous range of information on aircraft. On aeronautical charts, the availability of this facility is indicated by 
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.An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved