Definition
The point during an instrument approach where the aircraft, while flying level at a published intermediate altitude, meets the descending electronic or vertical guidance signal (the glideslope on an ILS, or the glidepath on an LPV/LNAV-VNAV approach) and begins the final descent to the runway.
Plain English
The moment your level-flight altitude crosses the descending guidance beam from the runway, and you start descending along that beam toward landing.
Context Anchor
Seen during instrument approaches, especially when the pilot is holding an assigned altitude until the descent guidance is reached.
Derivation
Intercept comes from Latin intercipere, meaning to seize or catch between. Here, the aircraft catches the descending guidance signal between two altitudes — the level segment above and the descent path below.
Why Pilots Care
Capturing the intercept at the correct altitude prevents being high or low on the approach and ensures a stable descent path to the runway.
Intuition Check
Do not read intercept as simply passing through the glideslope or glidepath. Here it means meeting the descent path at the planned point and then following it, normally from below.
Example Sentence 1
Level at 3,000 feet, the pilot watched the glideslope indicator come alive and began the descent at glideslope intercept.
Example Sentence 2
We planned our descent to arrive at the glidepath intercept exactly on altitude.