Definition
The speed at which an airplane is descending toward the ground, measured in feet per minute (fpm). During the landing flare, rate of sink refers specifically to how quickly the airplane is losing altitude in the final feet above the runway, and it must be reduced progressively to near zero at touchdown.
Plain English
How fast the airplane is going down. In the flare, the pilot uses elevator inputs to slow the descent so the airplane settles gently onto the runway instead of dropping onto it.
Context Anchor
Encountered during landing, especially in the round out or flare, when the pilot is reducing the airplane’s downward movement before the wheels touch the runway.
Derivation
Rate means an amount measured over time. Sink comes from an old word meaning to go down or settle lower. In aviation, the phrase points directly to how fast the airplane is settling downward through the air.
Why Pilots Care
A controlled rate of sink at touchdown prevents hard landings and reduces stress on the landing gear.
Intuition Check
Do not read “sink” as a plumbing fixture or as a vague feeling of dropping. Here it means actual downward movement of the airplane, measured over time.
Example Sentence 1
As the airplane crossed the runway threshold, the pilot began the round out to reduce the rate of sink before touchdown.
Example Sentence 2
A high rate of sink on final approach requires immediate power adjustment to avoid a hard landing.