The upslope endfire ILS glide slope: a non-image system that accommodates rising terrain below the approach path

The glide slope component of the instrument landing system (ILS) has traditionally presented the greatest technical challenge when providing landing guidance for an airport. A major reason is that the typical ILS glide slope makes use of the ground as an image-forming plane to increase the effective vertical aperture and thus the resolution available from the guidance signal. Not only is a reasonably smooth ground (± 1 foot) desired, but the most simple, classic, null reference image glide slope cannot tolerate much of an upslope in the terrain under the approach path. The intent of this paper is to describe the upslope endfire system, discuss its mechanization and to present the results of the full scale testing and the monitor validations