Definition
The speed at which an aircraft is closing on a desired course, radial, or bearing during the process of joining it. It is determined by the angle of intercept and the aircraft's groundspeed, and it governs how quickly the navigation needle will center as the course is approached.
Plain English
How fast you are moving toward the line you are trying to join. A steep angle and high speed mean you arrive at the line quickly; a shallow angle and slower speed mean you arrive at it gradually.
Context Anchor
Used in navigation when deciding how sharply to turn to join a course shown on an instrument, chart, or moving map.
Derivation
Intercept comes from the Latin intercipere, meaning 'to seize between' or 'to catch in the middle.' In navigation, you are catching the course as it passes by — the rate of intercept is simply how quickly that catching is happening.
Why Pilots Care
Controls how soon and smoothly you join the desired course without overshooting or requiring large corrections.
Analogy
It is like walking toward a painted line on the ground. If you approach at a shallow angle, you reach it slowly; if you approach more directly, you reach it sooner.
Intuition Check
Rate of intercept is not just the intercept angle. The angle helps determine it, but the rate is how quickly the aircraft is actually closing on the course.
Example Sentence 1
Seeing the needle move quickly toward center, the pilot reduced the intercept angle to slow the rate of intercept and avoid overshooting the radial.
Example Sentence 2
A slower rate of intercept on a shallow heading change allowed the aircraft to roll out precisely on the localizer without overshooting.