Plain English Meaning

Three numbers that describe how an aircraft is guided down to the runway: how steep the descent is, how high the aircraft is when it crosses the start of the runway, and where the descent line would touch the runway if you drew it all the way down.

Full Definition

A grouped set of three related parameters that describe a precision approach's vertical guidance geometry. Glide Slope (GS) is the angle of the descent path to the runway, expressed in degrees (typically around 3°). Threshold Crossing Height (TCH) is the height in feet at which the glide path crosses over the runway threshold. Runway Point of Intercept (RPI) is the point on the runway where the glide path, if extended, would intersect the runway surface. Together, these three values define the published descent geometry for a precision ( or -style) .