FLIGHT EVALUATION OF A BASIC C/A-CODE DIFFERENTIAL GPS LANDING SYSTEM FOR CATEGORY I PRECISION APPROACH.

Flight tests were conducted to evaluate the capability of local area C/A-code differential GPS (DGPS) to provide accuracy suitable for precision approach operations under Category I conditions. An aircraft was equipped with DGPS receiving equipment and additional computing capability that derived GPS-based instrument approach paths, converted DGPS position information to lateral/vertical deviations from the approach path, and drove the appropriate aircraft flight instruments. A mobile ground station using identical DGPS receiving equipment and a VHF data transmitter was employed to send differential corrections to the airborne system. Other than the differential corrections, no other augmentation of the airborne data was employed. Analysis of data collected from 82 hand-flown approaches using ground truth provided by theodolite or laser tracker shows that the system achieved vertical accuracies meeting Category I requirements with a substantial margin when narrow-correlator spacing GPS receivers were used. Lateral accuracies met Category III requirements.