Study on the Influence of Terrain Slope on the Size of Localizer Critical and Sensitive Area

The operational protection area of ILS localizer is a prescribed area near the localizer antenna, which included a critical zone and a sensitive zone. Such area prevents the possibility of unacceptable interference to the ILS signal during ILS operations, moving or stationary vehicles, aircraft and other objects during operation. ICAO Annex 10 has the following assumptions when defining a typical operational protection area: (1) The terrain is flat; (2) The glide path is 3°; (3) Allocations of 60 per cent of applicable tolerances for static multipath and 80 per cent for dynamic multipath; (4) An approaching aircraft at 105 knots. This paper uses software to analyze the impact of a single variable-the topographic slope of the airfield on the localizer operational protection area after excluding other influencing factors, and verifies the possibility of operational protection area reduction when the airfield slope is downhill, so that the efficiency of airport operations improvement can be achieved.