Definition
The calibrated stalling speed, or the minimum steady flight speed at which the airplane is controllable, with the landing gear extended, the wing flaps in the landing position, and the airplane in the configuration it would normally be in for landing. VS0 is published in the Pilot's Operating Handbook and is marked as the lower end of the white arc on the airspeed indicator.
Plain English
The slowest speed the airplane can fly without stalling when it is set up to land — gear down, flaps down, and trimmed for landing. Below this speed, the wing stops producing enough lift to keep flying.
Context Anchor
Seen in airspeed indicator markings, aircraft manuals, and discussions of approach and landing speeds.
Derivation
The 'V' comes from the French vitesse, meaning speed — the international convention for naming aircraft speed limits. The 'S' stands for stall. The '0' (sometimes written as a subscript) indicates the landing configuration, where flaps and gear are fully extended. So VS0 reads as 'velocity, stall, landing configuration.'
Why Pilots Care
It sets the minimum safe speed for final approach and is essential for determining landing distance and go-around decisions.
Grounding Statement
With the gear down and landing flaps selected, the airplane can usually fly slower than it can when clean, but below VS0 it can no longer maintain steady flight in that setup.
Intuition Check
The 0 in VS0 does not mean zero speed. It marks the landing configuration for this stall-speed value.
Example Sentence 1
On final approach, I aim for 1.3 times VS0 — that gives me a safe margin above the stall in the landing configuration.
Example Sentence 2
Before landing, the checklist confirmed that the computed approach speed remained well above VS0.