The invention relates to using radar derived location data in a GPS landing system. In aspects herein, if GPS signals used as inputs into a GPS landing system become unreliable, an aircraft instead uses signals derived from radar data to operate the GPS landing system. Generally, GPS signals are unreliable if they cannot be received or if the signals are corrupted. Instead of using GPS signals, the landing system uses radar derived location data as inputs. In one example, the radar derived location data is generated using a radar system located at the intended landing site, e.g., an airport or aircraft carrier. The landing site transmits this data to the aircraft which processes the data using its GPS landing system that outputs control signals for landing the aircraft. Thus, even when GPS signals are unreliable, the aircraft can use the GPS landing system to land.