If control cables are properly adjusted but control surfaces vibrate, what is the likely cause?

When control surfaces vibrate despite properly adjusted control cables, the issue is often associated with worn attachment fittings. Over time, attachment points and fittings can wear down due to continuous movement and stress, leading to play or slack in the control surfaces. This excess movement can result in vibrations as the surfaces do not remain stable during operation.

Vibrations initiated from worn fittings can significantly affect aircraft stability and control because the control surfaces must remain rigidly connected to function correctly. Addressing worn attachment fittings often involves inspecting and replacing them to mitigate any lost rigidity and ensure smooth operation of the control surfaces.

While loose connections or incorrect cable tension could lead to similar issues, they typically would manifest in different ways and are less likely to be the sole contributors to sustained vibration under the condition described. Misaligned control surfaces could also be a contributing factor, but if adjustments are made and the vibrations persist, it indicates deterioration at the attachment points is more probable.