Abstract: A method and a device for fault detection in the load path of a spindle actuator which is provided for actuating an aerodynamically active surface, in particular a high-lift flap of an aircraft, wherein the spindle actuator has a redundant load path which is formed by a spindle and a secondary connection which are connected rotationally fixedly to one another on the driven side and are coupled to the surface to be actuated and which are assigned separate load paths on the drive side, whereof the primary load path contains a primary spindle which is driven by a motor and can be fixed in its rotational movement by a primary brake, and the secondary load path contains the secondary inner connection, which is in particular arranged concentrically in the primary spindle, which can be fixed in its rotational movement by a secondary brake, in which output signals representing the turning position of the spindle, which are generated by means of at least one turning position sensor which is coupled to the primary spin