Definition
The speed at which the distance between the aircraft and a fixed point on the ground (or another object) is decreasing. When maneuvering by reference to ground objects, rate of closure is influenced by groundspeed and by the angle at which the aircraft is approaching the reference point.
Plain English
How quickly you are getting closer to something. A high rate of closure means the gap is shrinking fast; a low rate means you are approaching slowly.
Context Anchor
Used during ground-reference maneuvers when a pilot is judging how quickly the airplane is approaching a road, field boundary, point, or other ground reference.
Derivation
Closure comes from the Latin claudere, meaning to close or shut. The rate of closure is simply the speed at which the gap between two things is closing.
Why Pilots Care
Changes in rate of closure signal when to increase or decrease bank angle to compensate for wind and keep a constant radius around the reference point.
Grounding Statement
If a road ahead seems to be coming up quickly, your rate of closure with that road is high.
Intuition Check
Do not assume rate of closure means the airplane’s normal flying speed. It means how quickly the airplane is getting closer to a specific point or object, which can change with wind and direction of travel.
Example Sentence 1
On the base-to-final turn with a strong tailwind, the pilot noticed a high rate of closure on the extended centerline and steepened the bank to avoid overshooting.
Example Sentence 2
During S-turns the rate of closure to the road was used to time the rollout and apply the correct wind correction.