Definition
The maximum speed during the takeoff roll at which the pilot must decide whether to continue the takeoff or reject it. At or below V1, the takeoff can still be safely aborted within the remaining runway. Above V1, the takeoff must be continued, even if an engine fails, because there is no longer enough runway to stop safely.
Plain English
The speed during takeoff that marks your last chance to stop on the runway. If something goes wrong before you reach this speed, you can still abort. Once you pass it, you are committed to flying.
Context Anchor
You encounter V1 during takeoff planning, takeoff briefings, and high-speed takeoff operations in multiengine and turbine airplanes.
Derivation
The 'V' in V-speeds comes from the word 'velocity.' The '1' marks it as the first key decision point in the takeoff sequence, before the rotation speed (VR) and liftoff speed.
Why Pilots Care
It directly determines whether an engine failure results in a safe continued takeoff or a runway overrun during an abort.
Grounding Statement
During the takeoff roll, V1 is the point where stopping is still planned before it, and continuing is normally planned after it.
Intuition Check
V1 is not the speed where the pilot starts thinking about what to do. The decision criteria are set before takeoff; at V1 the pilot acts on that plan.
Example Sentence 1
The captain called 'V1' as the airspeed needle crossed the bug, and a moment later called 'rotate.'
Example Sentence 2
An engine failure after decision speed required the pilot to continue the takeoff and climb on the remaining engine.