DEVELOPMENT AND FLIGHT TEST OF A WEATHER RADAR PRECISION APPROACH CONCEPT

Advanced airborne radar approach (ARA) concepts are being developed and evaluated as a part of NASA's Rotorcraft All-Weather Operations Research Program. Conventional airborne weather/mapping radar is being investigated as a primary navigation aid in both the over-water and overland environments. As a result of research in this field, a novel precision approach concept has been developed and demonstrated in flight tests. This ARA concept, developed under a cooperative research agreement with the University of Nevada, derives localizer and glide slope guidance by amplitude comparison of directional X-band signals transmitted from the landing site. In principle, the ground station could be a series of precisely placed radar reflectors or an X-band radar transponder-based system. To demonstrate this concept, a transponder-based beacon landing system (BLS) has been built and flight tested. The BLS concept demonstration hardware consists of an add-on microprocessor, installed in conjunction with the aircraft weather/mapping radar, which analyzes the radar beacon-receiver returns and determines range, localizer deviation, and glide slope deviation. The ground station consists of an X-band radar beacon connected via a high-speed switching circuit to an array of five antennas. The beacon return pulses consist of omni signals for landing site location and directional returns for localizer and glide slope determination. Preliminary results from the flight test program show that the BLS concept has significant potential for providing rotorcraft with low-cost, precision instrument approach capability in remote areas.