Potential of Differential Global Positioning System for Category III Operations: Analysis of Flight Test Results

Abstract

The Federal Aviation Administration is conducting a program to investigate the feasibility of satellite-based navigation to support Category III precision landing applications. Category III (CAT III) refers to zero or nearzero visibility conditions. The program is evaluating the potential of the Differential Global Positioning System (DGPS) for CAT III precision approach and landing. Evaluations include flight tests, satellite simulator tests, and various analyses to supplement these tests.DGPS uses a ground reference station that computes corrections to satellite range measurements and transmits them to the aircraft, where they are used to augment the airborne GPS solution. DGPS can provide position accuracies of a few meters down to a small fraction of a meter, depending on the particular implementation.This paper presents flight test requirements, evaluation methods, and results. Flight test results for two code-based and two carrier-based DGPS systems are given, along with brief descriptions of each design. Code-based systems have the potential for submeter accuracy; carrier-based systems have the potential for subdecimeter accuracy. Results presented include measurements of sensor errors, flight technical errors, total system errors, and touchdown dispersion errors, as well as some assessments of system integrity. These are all measures of precision landing system performance. The results indicate the feasibility of using DGPS for CAT III applications.