Non-Destructive Testing of aircraft structures is of paramount relevance leading to key information regarding the structural characteristics and the residual life of a component. This paper is focused on the experimental and modeling activities related to vibrational analysis carried out on a typical aeronautical composite sample. A flap section of a regional aircraft has been studied applying the conventional tools of the modal analysis. The aeronautical component has been at first characterized in terms of natural frequencies and normal modes. Then it has been damaged using a drop tower that induced a controlled impact in the structural component. The vibrational analyses have been repeated and the normal modes in the two conditions have been compared. Then other approaches based on vibrational properties of the structures have been investigated to detect defect and damage.