Abstract :
Anyone who has occupied the window seat of a commercial plane has probably watched the way the wing moves up and down — slowly, like a majestic bird in unhurried flight. This isn´t necessarily unnerving, so long as the “flapping” remains reasonable. Aircraft wings are supposed to bend, the way tall buildings sway. If they didn´t, they´d break. But when the plane runs into turbulence and the wings start to flutter — you wonder. How much is too much? After ail, metal fatigue is real.
