Automatic Aircraft Landing over Parabolic Trajectory using Precise GPS Measurements

Global Positioning System (GPS) based aircraft landing is a methodology still not in use today despite the widespread use of GPS. This is primarily because a standard single frequency Global Positioning System (GPS) receiver provides a positioning accuracy of approximately 4-20 m which is not acceptable by aviation standards for precision landings. The accuracy of GPS can be further enhanced with dual frequency receivers which are able to provide accuracy around 1-12 m. However, these errors are still quite large when it comes to critical safety of life applications. Differential GPS (D-GPS) allows for precise positioning us ing information from reference stations on the ground along with satellite signals. Carrier phase tracking is one such D-GPS approach which allows range determination with centimeter level accuracy. However, carrier phase measurements require estimation of unknown fixed integer ambiguities before the receiver can start determining its position. Using single difference smoothed pseudorange measurements the integer ambiguities can be estimated with reasonable accuracy. This methodology brings the position error down to centimeter level which can meet the Federal Aviation Authority (FAA) regulations for Category-III (CAT-III) precision approaches. This paper examines an aircraft automatic landing using single differenced smoothed pseudorange measurements as the primary navigation source for an aircraft. The use of a parabolic descent trajectory is explored. Simulations demonstrate positioning with centimeter level accuracy using smoothed pseudorange measurements which enable a fully automatic landing. The accuracy is found to be dependent on the autopilot errors rather than the positioning system errors. General Terms Algorithm, Measurement, Performance, Reliability