Definition
The minimum airspeed at which an aircraft can maintain level flight in the landing configuration — gear down and flaps fully extended — at maximum gross weight. It is represented by the lower end of the white arc on the airspeed indicator and is designated VS0.
Plain English
The slowest speed the aircraft can fly without stalling when it is set up to land, with the wheels and flaps down.
Context Anchor
Seen in airspeed indicator color-code discussions, aircraft manuals, and landing-speed planning.
Derivation
“Flap” refers to a movable part on the wing that can be lowered to change how the wing produces lift. “Stall” in aviation means the wing is no longer producing smooth, usable lift because the airflow over it has broken down. Together, “flaps-down stall speed” points to the stall speed with the landing flaps lowered.
Why Pilots Care
It sets the bottom of the safe speed range for approach and landing; flying slower risks a sudden loss of lift.
Grounding Statement
Below this speed the wing can no longer support the airplane in level flight with flaps extended.
Intuition Check
Do not read “stall” here as the engine stopping. A flaps-down stall speed is about the wings losing lift, not the engine quitting.
Example Sentence 1
The bottom of the white arc on the airspeed indicator marks the flaps-down stall speed for this aircraft.
Example Sentence 2
At maximum landing weight the flaps-down stall speed increased by five knots.