Definition
The segment of an airport traffic pattern flown perpendicular to the landing runway, connecting the downwind leg to the final approach leg. It is normally flown at the same altitude as the downwind until the pilot begins the descending turn onto final.
Plain English
The short crosswise leg of the rectangular pattern flown around an airport, where the aircraft turns off the downwind, lines up roughly at right angles to the runway, and prepares to turn onto final approach for landing.
Context Anchor
You encounter this term when flying or receiving instructions in the airport traffic pattern, especially while preparing to turn from downwind toward final.
Derivation
From the geometry of the rectangular traffic pattern: the runway is the 'base' line, and this leg runs perpendicular to it, like the base of a rectangle joining the two long sides (downwind and final).
Why Pilots Care
Correct positioning and timing on base maintains safe spacing with other traffic and produces a stabilized approach.
Intuition Check
“Base leg” does not mean the most important or basic part of the flight. It is a named segment of the airport traffic pattern, between downwind and final.
Example Sentence 1
Cessna Three-Two-Alpha, turn base, runway two-seven, cleared to land.
Example Sentence 2
ATC reported traffic on the base leg, so we extended our downwind to create more spacing.