Integrated enroute and approach guidance system for aircraft

Abstract

Data from long range aids such as the global positioning system (GPS) and an inertial navigation system (INS) and short range aids such as a microwave landing system (MLS) are used to smoothly and automatically transition an aircraft from the long range aids to the short range aids. During cruise a Kalman filter combines data from the global positioning system and the inertial navigation system to provide accurate enroute information. When the aircraft arrives in the vicinity of the airport and begins to acquire valid data from the microwave landing system, the Kalman filter is calibrated with the MLS data to permit Precision landing with GPS/INS data alone in case the MLS system subsequently fails. In addition, navigation information begins to be derived from a weighted sum of the GPS/INS and MLS data, the weighting being determined by distance from the airport. In a first region farthest from the airport, the GPS/INS data is given a 1.0 weighting factor; and in a second region nearest the airport, the MLS data is given a 1.0 weighting factor. In a third region intermediate the first and second regions, the GPS/INS data and MLS data are proportionately and complementarily weighted as a function of the distance from the airport. If the MLS system fails, the weighting system is disabled and navigation data is again derived from the GPS/INS combination. In addition, the data from both systems are monitored, and a cockpit alarm is sounded if the data diverges beyond a specified amount.