Aircraft comprising a fuselage a first and a second wing (1, 3) extending away from the fuselage on opposite sides thereof, each wing (1, 3) being provided with at least one movable flap element (7, 9) arranged on the wing (1, 3) and being movable relative to the wing (1, 3) between a retracted position and an extended position, wherein each of the at least one the flap element (7, 9) comprises a flap (7, 9), drive means having a movable driven output (21, 23), an actuation assembly (25, 27, 47, 49) connecting the output (21, 23) of the drive means with each of the at least one flap element (7, 9) on the wings (1, 3), the actuation assembly (25, 27, 47, 49) being configured such that a movement of the output (21, 23) of the drive means effects a movement of each of the at least one flap element (7, 9) between the extended and the retracted positions, wherein each of the flap elements (7, 9) is provided with a sensor element fixedly mounted on it, wherein each sensor element is capable of providing a sensor signal which corresponds to the vibrations at the position of the sensor element on the flap element (7, 9), excitation means capable of exciting vibrations of the output (21, 23), the vibrations being in a defined frequency interval, and a control unit connected with the excitation means and each sensor element, wherein the control unit is adapted to compare for each sensor element during operation of the excitation means the amplitude of the vibrations in the defined frequency interval detected by that sensor element with a predetermined threshold of that sensor element and to provide a failure signal when for at least one sensor signal the amplitude is below the threshold of that at least one sensor signal. a fuselage a first and a second wing (1, 3) extending away from the fuselage on opposite sides thereof, each wing (1, 3) being provided with at least one movable flap element (7, 9) arranged on the wing (1, 3) and being movable relative to the wing (1, 3) between a retracted position and an extended position, wherein each of the at least one the flap element (7, 9) comprises a flap (7, 9), drive means having a movable driven output (21, 23), an actuation assembly (25, 27, 47, 49) connecting the output (21, 23) of the drive means with each of the at least one flap element (7, 9) on the wings (1, 3), the actuation assembly (25, 27, 47, 49) being configured such that a movement of the output (21, 23) of the drive means effects a movement of each of the at least one flap element (7, 9) between the extended and the retracted positions, wherein each of the flap elements (7, 9) is provided with a sensor element fixedly mounted on it, wherein each sensor element is capable of providing a sensor signal which corresponds to the vibrations at the position of the sensor element on the flap element (7, 9), excitation means capable of exciting vibrations of the output (21, 23), the vibrations being in a defined frequency interval, and a control unit connected with the excitation means and each sensor element, wherein the control unit is adapted to compare for each sensor element during operation of the excitation means the amplitude of the vibrations in the defined frequency interval detected by that sensor element with a predetermined threshold of that sensor element and to provide a failure signal when for at least one sensor signal the amplitude is below the threshold of that at least one sensor signal.