An autothrottle system for an aircraft, comprising: a motor configured to impart rotational movement to a shaft extending from the motor, the motor being mounted on a support; an actuator assembly operatively connected to the shaft and to an attachment end of a throttle lever, the throttle lever having a control end, opposite to the attachment end, for application of manual force; an electronic controller configured to control the motor to cause movement of the throttle lever so that the motor moves the actuator assembly along the shaft based at least in part on an engine operating parameter monitored by the controller, wherein the actuator assembly comprises: a bearing assembly having a plurality of bearings configured to contact a surface of the shaft for converting rotational movement of the shaft into linear motion of the bearing assembly along the shaft; and a shuttle arm (34; 34') having a mounting surface at a first end configured to attach to the bearing assembly and at least one linkage arm (52; 52') at a second end of the shuttle arm (34; 34') which is operatively coupled to the attachment end of the lever, and characterised by the shaft surface being smoothly continuous and longitudinally unbroken along its elongation so as to allow the actuator assembly to longitudinally slip along the shaft elongation irrespective of any shaft rotation that may be concurrently imparted by the motor when a thrust force that the bearings apply to and against the shaft is exceeded by a linear force manually applied at the throttle lever to the actuator assembly. a motor configured to impart rotational movement to a shaft extending from the motor, the motor being mounted on a support; an actuator assembly operatively connected to the shaft and to an attachment end of a throttle lever, the throttle lever having a control end, opposite to the attachment end, for application of manual force; an electronic controller configured to control the motor to cause movement of the throttle lever so that the motor moves the actuator assembly along the shaft based at least in part on an engine operating parameter monitored by the controller, wherein the actuator assembly comprises: a bearing assembly having a plurality of bearings configured to contact a surface of the shaft for converting rotational movement of the shaft into linear motion of the bearing assembly along the shaft; and a shuttle arm (34; 34') having a mounting surface at a first end configured to attach to the bearing assembly and at least one linkage arm (52; 52') at a second end of the shuttle arm (34; 34') which is operatively coupled to the attachment end of the lever, and characterised by the shaft surface being smoothly continuous and longitudinally unbroken along its elongation so as to allow the actuator assembly to longitudinally slip along the shaft elongation irrespective of any shaft rotation that may be concurrently imparted by the motor when a thrust force that the bearings apply to and against the shaft is exceeded by a linear force manually applied at the throttle lever to the actuator assembly. a bearing assembly having a plurality of bearings configured to contact a surface of the shaft for converting rotational movement of the shaft into linear motion of the bearing assembly along the shaft; and a shuttle arm (34; 34') having a mounting surface at a first end configured to attach to the bearing assembly and at least one linkage arm (52; 52') at a second end of the shuttle arm (34; 34') which is operatively coupled to the attachment end of the lever, and characterised by the shaft surface being smoothly continuous and longitudinally unbroken along its elongation so as to allow the actuator assembly to longitudinally slip along the shaft elongation irrespective of any shaft rotation that may be concurrently imparted by the motor when a thrust force that the bearings apply to and against the shaft is exceeded by a linear force manually applied at the throttle lever to the actuator assembly.