Linear actuators

A linear actuator comprising:

• rotary motion producing means;
• linear motion producing means coupled with said rotary motion producing means for converting said rotary motion to linear motion, said linear motion producing means comprising a threaded shaft and nut arrangement;
• a driven member movable linearly by said linear motion producing means between a first position and a second position, said driven member being coupled to one of said shaft and nut arrangement;
• and
• back-drive means for returning said driven member to said first position in the event of a fault;
• characterised in that:
• said linear motion producing means includes torque reaction means which, in normal operation, is in an activated condition and provides a torque reaction path to enable the driven member to be reversibly moved between said first and said second positions, the driven member being restrained from rotating, but which, in the event of a fault, is in a de-activated condition so that it no longer provides said torque reaction path and said back-drive means can move the driven member to said first position, without disengaging the rotary motion producing means.