Autolanding a 737 using GPS and Integrity Beacons

Abstract

Differential GPS and miniature, low-cost Integrity Beacon pseudolites were used to carry out 110 successful automatic landings of a United Boeing 737-300 aircraft. The goal was to demonstrate Required Navigation Performance including accuracy and integrity-for Category I11 Precision Landing using GPS. These autopilot-in-the-loop flighe tests using GPS Integrity Beacons (low-power, ground-based marker beacon pseudolites placed under the approach path) furnish evidence that GPS can provide the full performance necessary to meet the stringent specifications of Category 111. It has been demonstrated that Integrity Beacons can provide consistent accuracies on the order of a few centimeters. But perhaps even more important, this centimeter-level accuracy coupled with the built-in geometrical redundancy provided by Integrity Beacon ranging provides an exceptional level of intrinsic system integrity. This integrity is calculated to be easily better than the required one part in a billion probability of missed detection. Passenger safety is improved significantly because this level of integrity is achieved independently from ground-based monitors through Receiver Autonomous Integrity Monitoring (RAIM). For the flight tests, the GPS receiver and single-channel navigation computer calculated precise positions and calculated glide path deviations. An analog interface provided ILS localizer and glideslope signals to the autopilot. The 737 was equipped with a dual-channel flight control system which was previously certified for Category IIIA landings. The autolands were performed through touchdown without rollout guidance, The series of 110 automatic landings were carried out at NASA's Crows Landing facility in California over a four-day period during the week of October 10, 1994. A laser tracker was used as an independent means for characterizing flight performance. The feasibility demonstration was sponsored by the FAA.