A screw actuator 16 comprises a screw shaft 17 for threaded engagement with an actuator output device 21 such that rotation of the screw shaft 17 causes linear movement of the actuator output device 21; and a motor 12 for driving rotation of the screw shaft 17. A no-back device 10; 20; 30 is included for restricting movement of the screw shaft 17 in response to feedback torque applied due to external forces on the actuator output device 21, and the no-back device 10; 20; 30 comprises a brake 104, 108; 314, 308 and a brake controller 22; 212 the brake 104, 108; 314, 308 comprising a no-back device brake member 104; 314 for engagement with a screw shaft brake member 108; 308 connected to the screw shaft 17 in order to generate a braking torque on the screw shaft 17 when the brake members 104, 108; 314, 308 engage with one another, and a biasing device 102; 202; 302 for providing a force to urge the brake members 104, 108; 314, 308 to engage with one another when the motor 12 is not activated, this force hence resulting in a braking torque that resists rotation of the screw shaft 17 under feedback torque; and the brake controller 22; 212 being arranged to provide a force to urge the brake members 104, 108; 314, 308 to disengage with one another, this force being applied upon activation of the motor 12 for rotating the screw shaft 17, in order that the braking torque is reduced when the motor 12 is activated.
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