A self-locking actuator for moving a flight control surface of an aircraft and for self-locking in response to an external load applied to the actuator. The actuator includes a motor, a screw, and a drive gear that is rotatably driven by the motor to rotationally couple with the screw. A pawl support is coupled to and rotatable with the screw, and a swivel assembly is coupled to the pawl support for rotational movement with the screw and pivoting movement relative to the screw. The swivel assembly engages a cage that is fixed relative to the rotating screw, drive gear, and swivel assembly. Pivoting of the swivel assembly about a pivot axis engages the swivel assembly with the cage to positively lock with the cage and to prevent rotation of the screw in each of first and second opposite rotational directions of the screw about a rotational axis of the screw.