During last years, structure of flight commands is becoming complex and complex and diagnostic and prognostic methods are the most important instruments to save time and money. The structure of the considered flight command is composed by an electric motor that receives the pilot input and actuates a flapper-nozzle valve; successively, obstruction of one nozzle leads to the movement of the spool, opening two passageways that actuate the jack. This permits to modify the surface of the aircraft wings. The aim of this thesis is to model in a satisfying way this structure; in particular, two models are present: a High-Fidelity model, more accurate but too complex, used as a reference and a Low-Fidelity model that is less accurate but very useful to perform the prognostic algorithm.