Abstract: A dual I.L.S. glide slope system for allowing a normal 3.degree. descent path plus an additional 6.degree. descent path which can be used for noise abatement procedures etc. In accordance with the present invention these glide slopes are provided on a single assigned R.F. channel with no inverted courses interposed. The first signal null will occur at 9.degree. elevation when all signals will be zero, producing a "flag" alarm.

Abstract: A guidance system for aircraft and ships, which system comprises at least two localizer antenna arrangements which are spaced in elevation above a reflecting surface, at least two distance measuring antenna arrangements which are spaced in elevation above the reflecting surface, and at least two glide slope antenna arrangements which are mounted vertically above each other, the guidance system being such that the localizer antenna arrangements are at a mean height of at least 21/2 wavelengths above the reflecting surface and are fed with signals having the same radio frequency but having a phase difference, the distance measuring antenna arrangements are at a mean height of at least 25 wavelengths above the reflecting surface and are fed with signals having the same radio frequency but having a phase difference, and the glide slope antenna arrangements are fed with signals having the same radio frequency but two different frequencies of amplitude modulation to give by reflection from the reflecting surface at