Definition
The angle, measured in degrees, to which the wing flaps are extended downward from their retracted position. Common settings include partial extensions (such as 10° or 20°) used for takeoff and initial approach, and larger extensions (such as 30° or 40°) used for final approach and landing. Greater deflection increases both lift and drag, lowers the stall speed, and steepens the descent path.
Plain English
How far down the flaps are lowered, measured as an angle. A small angle means the flaps are barely lowered; a large angle means they are lowered a lot.
Context Anchor
Seen in takeoff, approach, and landing procedures when choosing the flap setting for the airplane and conditions.
Derivation
Deflection comes from the Latin deflectere, meaning to bend aside or turn away. The flap is bent away from its normal in-line position with the wing, and the degree describes how far it has been bent.
Why Pilots Care
The chosen angle changes lift, drag, and stall speed, directly affecting required runway length, approach speed, and climb performance after takeoff.
Intuition Check
Do not read “degree” as temperature or a level of training; here it means an angle measurement. More flap deflection is not automatically better—the correct amount depends on the procedure, runway, weight, and conditions.
Example Sentence 1
On final approach, the pilot selected a greater degree of flap deflection to steepen the descent without gaining airspeed.
Example Sentence 2
Reducing the degree of flap deflection from 30 to 10 after liftoff helped the airplane climb more efficiently.