Performance of Category IIIB Automatic Landings Using C/A-Code Tracking Differential GPS

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Abstract
An experimental DGPS precision approach and landing system was installed and flight tested on the NASA Langley Transport Systems Research Vehicle (TSRV). The GPS ground reference station and avionics units used 10-channel, narrow-correlator, C/A-code tracking receiver engines. The avionics drove the aircraft flight control system with ILS “look-alike” vertical and horizontal angular deviations derived solely from DGPS C/A-code tracking position and velocity. The avionics did not make use of kinematic carrier-phase tracking with on-the-fly cycle ambiguity resolution techniques. A total of 40 DGPS-guided approaches and landings were performed at the NASA Wallops Flight Facility, 31 of them hands-off, automatic landings. Total system error, measured by laser tracker, met the proposed Category III required navigation performance (RNP) or “tunnel concept” accuracy requirements by substantial margins. Touchdown dispersion for the 31 automatic landings also met Category III RNP requirements with significant margin.

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