Abstract: A system for assisting the maintenance of an aircraft is configured for implementing the following steps in an iterative manner determining a spectral power density of the position of a control surface over a time window; when the spectral power density corresponds to an amplitude of oscillations of the control surface upwardly crossing this predetermined threshold, storing an excess amplitude start time; and when the spectral power density corresponds to an amplitude of oscillations of the control surface downwardly crossing this predetermined threshold: determining a time interval between the excess amplitude start time and an excess amplitude end time, during which the amplitude of oscillations of the control surface has remained above the predetermined threshold; and determining an indicator representative of the energy corresponding to these oscillations during the time interval.