Definition
A recessed cavity or housing built into the underside of the wing into which the flap retracts and sits flush when fully raised, leaving a clean aerodynamic surface.
Plain English
The pocket in the wing where the flap tucks away when it's pulled up, so the bottom of the wing stays smooth.
Context Anchor
Seen in flap system descriptions, aircraft inspections, and discussions of how flaps fit into the wing.
Derivation
‘Well’ here uses an older mechanical sense — a recessed space or cavity that something fits into (like a wheel well). It signals a built-in pocket, not a hole or shaft.
Why Pilots Care
A clean, unobstructed flap well allows the flap to retract fully, preserving the wing’s smooth upper surface and intended cruise performance.
Intuition Check
Do not read “well” as a water well. In this term, a well is a recessed space built into the aircraft structure.
Example Sentence 1
After landing in heavy rain, the pilot checked the flap wells for trapped water and debris before the next flight.
Example Sentence 2
With the flaps fully retracted, the trailing edge of the wing appeared smooth because the flaps sat flush inside the flap wells.