false glide-slope

false glide-slope

A characteristic of the glide-slope portion of the ILS (instrument landing system), in which one or more false glide-slopes at different angles to the horizontal occur well above the true glide-slope. This is because of a radiation pattern of the antenna and the ground reflection of some of the transmitted energy, resulting in more than one overlapping lobe. The false glide-slopes occur at odd multiples of the true glideslope angle (typically 3°) (i.e., at 9° and 15°). At even multiples (6°, 12°), a centered glide-slope needle occurs, but this is because of a null signal; reverse sensing is present above and below these glide-slopes. A pilot can easily recognize this false indication by the steeper-than-normal rate of descent. Pilots will not experience false glide-slopes below the true glide-slope angle. Pilots can avoid encountering a false glide-slope by following published approach procedures.