A new landing aid based on GPS is being developed that will replace the common Instrument Landing System (ILS), which is now in use at most of the worlds airports. The new program is the GPS Landing System (GLS), or more generically, the Global Navigation Satellite System (GNSS) Landing System (to include the Galileo and GLONAS satellite systems).

GLS makes use of the high accuracy of the GNSS to calculate the aircrafts 3-D position relative to the defined approach path to the runway threshold. The defined path is sent to the GLS by the airport or stored in an onboard database. The onboard GLS then provides the vertical and horizontal deviations from centerline to aircraft displays for review by the pilot, and to the Autoland and HGS to use in guiding the aircraft to the runway. The GLS can provide these deviations with the same scaling as the ILS to simplify the transition from ILS to GLS.