Transponder Landing System (TLS)
The Transponder Landing System (TLS) is a new precision landing system which provides Instrument Landing System (ILS) type guidance signals (Category I) to the aircraft. TLS computes aircraft position based on received aircraft transponder replies at the TLS azimuth and elevation sensors. Guidance signals are issued to the aircraft through ILS type signals. The flight crew uses the standard ILS displays to fly the TLS approach.
There are approximately 18 potential TLS sites designated by Congress. Since the TLS system only provides guidance to one- aircraft at a time and the system requires a ground-based operator to enter the designated TLS aircraft transponder code, all designated sites may not be ideal candidates for TLS whereas an ILS may provide the benefit the airport desires.
The Avionics Engineering Center has assisted the FAA in the test and evaluation of TLS. Evaluation included the effects of aircraft (other than the aircraft on approach) on the tracking algorithms due to overlapping transponder replies.