the actuator of the invention is described herein in an application to moving a flight control surface relative to the structure of an aircraft . the flight control surface is movable between a deployed position and a neutral or retracted position . with reference to the figures , the electromechanical actuator comprises a body 1 and an electric motor 2 having a stator fastened to the body 1 and a rotor rotatably connected to a motion transmission element . the body 1 has conventional means for fastening it to the structure of an aircraft . the electric motor 2 is powered by a control unit ( not shown ) that is connected to the electricity network of the aircraft for its own power supply and for powering the actuator , and that is connected to the cockpit of the aircraft to receive orders therefrom for deploying or retracting the flight control surface . in this example , the motion transmission element is a shaft 3 pivotally mounted in the body 1 and connected to the flight control surface via a motion transmission assembly ( not shown ). by way of example , the motion transmission assembly comprises a stepdown device and / or a motion transformation device such as a screw - and - nut assembly , and has an inlet element rotatably connected to the shaft 3 and an outlet element e . g . connected to the free end of a lever that is connected to the flight control surface . the shaft 3 is guided in rotation relative to the body 1 by bearings ( not shown ) and it is connected to the body 1 via a unidirectional transmission member , specifically in this example a freewheel given overall reference 4 , a torque limiter given overall reference 5 , and a brake device given overall reference 6 . the freewheel 4 comprises an inner portion 4 . 1 secured to the shaft 3 , an outer portion 4 . 2 pivotally mounted on the inner portion 4 . 1 , and a ratchet assembly allowing the outer portion 4 . 2 to turn in only one direction of rotation . the torque limiter 5 is a magnetic torque limiter having a first plate 5 . 1 provided with a first series of magnets 7 . 1 and a second plate 5 . 2 provided with a second series of magnets 7 . 2 . the first plate 5 . 1 is fastened to the outer portion 4 . 2 of the freewheel 4 , and the second plate 5 . 2 is connected to rotate with an inner ring 6 . 1 of the brake device 6 . the first series of magnets 7 . 1 extends substantially facing the second series of magnets 7 . 2 and is spaced apart therefrom by an airgap 7 . 3 . the magnetic field produced by the magnets and the width of the airgap 7 . 3 define a maximum torque that can be transmitted from the first plate 5 . 1 to the second plate 5 . 2 . sealing means are provided to prevent particles collecting on the magnets and interfering with the operation of the torque limiter 5 . in addition to the movable ring 6 . 1 , the brake device 6 has an outer ring 6 . 2 that is rigidly fastened to the body 1 ( more precisely , the outer ring 6 . 2 in this example is a portion of the body 1 ) and an outer ring 6 . 3 fastened to the body 1 with axial clearance . the inner ring 6 . 1 is fastened with axial clearance to the second plate 5 . 2 ( the inner ring 6 . 1 is more precisely engaged in a fluted portion of the second plate 5 . 2 ) and has a portion with faces that are each provided with a friction lining and that extend between friction linings carried by the outer rings 6 . 2 and 6 . 3 . springs 6 . 4 extend between the body 1 and the outer ring 6 . 3 to clamp the inner ring 6 . 1 between the outer rings 6 . 3 and 6 . 2 . the brake device 6 also has an electrical activator member 6 . 5 in the form of a solenoid dimensioned so that when it is powered it attracts the outer ring 6 . 3 and moves it away from the inner ring 6 . 1 against the force exerted by the springs 6 . 4 . in operation , when the activator member 6 . 5 is powered , the shaft 3 can pivot in both directions of rotation ( it should be observed that in the direction passed by the freewheel 4 , the motor 2 delivers little or no drive to the inner ring 6 . 1 and the torque limiter 5 ) and , when the activator member 6 . 5 is not powered , the freewheel 4 opposes rotation of the shaft 3 in one of the two directions of rotation . thus , when the activator member 6 . 5 is powered , the electric motor 2 , which is also powered , drives the shaft 3 to turn in either of its directions of rotation . when the activator member 6 . 5 is not powered , the electric motor 2 is likewise not powered so that only aerodynamic forces acting on the flight control surface can cause the shaft 3 to pivot . because of the freewheel 4 opposing turning of the shaft 3 in one of the two directions of rotation , the shaft 3 prevents the flight control surface from moving away from its neutral position towards its deployed position , whereas the flight control surface is left free to move towards its neutral position . nevertheless , if the aerodynamic forces acting on the flight control surface exert a torque on the shaft 3 that is greater than the maximum torque that can be transmitted between the plates 5 . 1 and 5 . 2 of the torque limiter 5 , the first plate 5 . 1 will pivot relative to the second plate 5 . 2 , thus allowing the shaft 3 to turn and allowing the flight control surface to move towards its deployed position . as a result , the torque limiter 5 limits the torque that can be transmitted to the structure of the aircraft and to the body 1 via the shaft 3 , the freewheel 4 , and the brake device 6 when the activator member is not powered . with reference to fig1 , and in the first embodiment , the airgap 7 . 3 extends in a plane perpendicular to the axis of rotation a of the shaft 3 . in this example , the first plate 5 . 1 is in the shape of a disk that is perpendicular to the axis a and that is pierced at its center to be fastened on a bushing secured to the outer portion of the freewheel 4 . the second plate 5 . 2 is also in the form of a disk that is perpendicular to the axis a and that is pierced at its center so as to be fastened to a bushing pivotally received in a bearing fastened to the body 1 . the end portion of the bushing remote from the second plate 5 . 2 is fluted to receive the inner ring 6 . 1 in axial sliding . in the variant of fig2 , the second plate 5 . 2 has the same shape as above . in this variant , the first plate 5 . 1 is in the form of an annulus centered on the axis a . the first plate 5 . 1 has an inner edge that extends around the bushing of the second plate 5 . 2 leaving a space that is occupied by a sealing gasket , and an outer edge that is fastened to the collar of a bushing secured to the outer portion of the freewheel 4 . a bearing is mounted between the bushing of the second plate 5 . 2 and the bushing of the first plate 5 . 1 . the second plate 5 . 2 is also in the form of a disk that is perpendicular to the axis a and that is pierced at its center in order to be fastened on a bushing pivotally received in a bearing fastened to the body 1 . the end portion of the bushing remote from the second plate 5 . 2 is fluted for receiving the inner ring 6 . 1 in axial sliding . with reference to fig3 and in a second embodiment , the airgap 7 . 3 extends in a cylindrical surface centered on the axis of rotation a of the shaft 3 . in this embodiment , the first plate 5 . 1 is in the form of a tube centered on the axis a and fastened to the outer portion of the freewheel 4 . the second plate 5 . 2 is also in the form of a tube centered on the axis a : the second plate 5 . 2 surrounds the first plate 5 . 1 and is pivotally received in a bearing secured to the body 1 . the end portion of the second plate 5 . 2 is fluted to receive the inner ring 6 . 1 in axial sliding . sealing gaskets are mounted between the plates 5 . 1 and 5 . 2 to oppose particles penetrating into the airgap 7 . 3 . in the variant of fig4 , the second plate 5 . 2 has the same shape as above . the first plate 5 . 1 is likewise of annular shape centered on the axis a , but it extends around the second plate 5 . 2 . the first plate 5 . 1 has one end carried by a collar secured to a bushing secured to the outer portion of the freewheel 4 . a bearing is mounted between the bushing of the second plate 5 . 2 and the bushing of the first plate 5 . 1 . naturally , the invention is not limited to the embodiments described but covers any variant coming within the ambit of the invention as defined by the claims . in particular , the magnetic torque limiter may be mounted downstream from the one - way transmission member or between the brake device and the body . the one - way transmission member may make use of pawls , rollers , or of chocking elements .