Study of Glide-Slope Monitor Failures Due to Weather

摘要

Monitors for ILS glide-slope equipments are often subject to false alarms when precipitation covers the ground in the radiation field of the glide-slope antennas. This report serves to delineate the problem and to offer some ameliorating recommendations. In particular, emphasis is placed on preventing false alarms from the on-path course position monitor and from the off-path clearance/width monitor. Analysis points to the monitor-area reflecting zone of ground cover as the cause for false alarms. Recommendations point to the development of glide-slope antennas with built-in RF probe loops to sample the antenna signals and transmission-line combinations of these samples to simulate the effects of the reflecting zones, as would be obtained with airborne reception, in the approach region. Detection of such combinations of pickup-loop samples serves to monitor the signals, assuming that the structure of the antenna assemblies remained undisturbed; additional monitor devices are recommended for measuring the stability of the physical structures. (Author)