The interaction between elastic aircraft parts and the air they pass through, which can cause the structural failure of said parts.
Aeroelasticity refers to the interaction of a flexible, elastic object (such as an aircraft wing, horizontal-stabilizer, or rudder) with a flowing stream of air. This can cause various parts of an aircraft to oscillate, or flutter; if left undamped, these oscillations can quickly grow to a magnitude sufficient to cause a structural failure of the part(s) in question.
Another important aeroelastic effect is control-reversal, where the aerodynamic forces generated by extending one or more control-surfaces are sufficient to twist the wing or stabilizer on which the control surface(s) are mounted, resulting in the aircraft turning in the direction opposite to that intended.
