Definition
The speed at which an aircraft is approaching, or being approached by, a reference point or another object. In maneuvering flight along a road or line feature, it refers to how quickly the aircraft is closing on a turn point or ground reference, which depends on groundspeed, wind, and angle of approach.
Plain English
How fast you are getting closer to something. The bigger the closure rate, the less time you have before you reach it.
Context Anchor
Seen in ground reference maneuvers such as eights along a road, where the pilot judges how quickly the airplane is approaching the road while correcting for wind.
Derivation
From the verb 'close' meaning to draw near or shut a gap, plus 'rate' meaning a measure of speed. Together: the speed at which a gap is closing.
Why Pilots Care
Managing closure rate lets the pilot adjust bank angle to keep the desired ground track without overshooting or drifting during maneuvers.
Grounding Statement
If a tailwind is pushing the airplane toward the road, the road may appear to come up faster because the distance to it is decreasing more quickly.
Intuition Check
Closure rate is not the same as the airplane’s speed through the air. It is how fast the distance between the airplane and the ground reference is shrinking.
Example Sentence 1
With a strong tailwind on the downwind leg of the maneuver, the pilot noticed a high closure rate on the next turn point and began the turn earlier than planned.
Example Sentence 2
If the closure rate feels too quick, the airplane will cross the road before completing the turn.