High Quality Content by WIKIPEDIA articles! The Transponder Landing System (TLS) is an all-weather, precision landing system that uses existing airborne transponder and ILS equipment to create a precision approach at a location where an ILS would normally not be available.Conventional ILS systems broadcast using a number of "single purpose" antennas. One, located just off the end of the runway, provides a fan-shaped signal for azimuth direction (side to side) and another located beside the runway provides elevation to indicate a standard glideslope. ILS installations also include one or more "marker beacons" located off the end of the runway to provide distance indications as the aircraft approaches the runway. This complex set of antennas is expensive to install and maintain, and are often difficult to site in built-up areas.