Definition
A condition in which the wing flaps on one side of the airplane extend or retract while the flaps on the other side fail to move with them, resulting in unequal lift between the two wings and a strong rolling and yawing tendency toward the wing with less flap deflection.
Plain English
The flap on one wing moves but the flap on the other wing does not, so one wing produces more lift than the other and the airplane wants to roll and turn toward the side with the smaller flap setting.
Context Anchor
Encountered during flap extension or retraction, especially when the airplane starts rolling unexpectedly after the pilot selects a flap setting.
Derivation
Asymmetrical comes from the Greek 'a-' meaning 'not' and 'symmetria' meaning 'same measure on both sides.' In aviation it means the two wings are no longer doing the same thing — one flap is out of step with the other.
Why Pilots Care
Asymmetrical flaps create an uncommanded roll that must be countered immediately with aileron and rudder to maintain directional control, especially during takeoff or landing when airspeed is low.
Intuition Check
Do not read “asymmetrical” as just uneven-looking. Here it means the left and right flaps are actually in different positions, which can affect control of the airplane.
Example Sentence 1
When the pilot selected flaps for landing, the airplane rolled sharply to the left, indicating asymmetrical flaps.
Example Sentence 2
After a flap motor failure on one side, asymmetrical flaps required the pilot to apply steady left aileron to keep the wings level on final approach.