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 (PAR or ILS-style) approach.
Plain English
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.
Context Anchor
Seen on instrument approach chart profile views, including radar approach information, where the final descent path is shown or described.
Why Pilots Care
Knowing these values lets the pilot verify the radar controller’s guidance and anticipate the exact height and touchdown point on the runway.
Intuition Check
GS can also mean ground speed in aviation. In GS/TCH/RPI, GS means glide slope—the descent path angle, not the airplane’s speed over the ground.
Example Sentence 1
Before flying the radar approach, the pilot reviewed the GS/TCH/RPI values to understand the descent angle and where the glide path would cross the threshold.
Example Sentence 2
The pilot cross-checked the published GS/TCH/RPI against the PAR display to confirm the aircraft was on the proper glide path.