A linear electromechanical actuator with a main screw-nut assembly driven by a main motion device and having a hollow screw with an abutting surface; an anti-jamming piston arranged coaxially within the screw and shiftable between an engaged position in which locking dogs interfere with the abutting surface and a disengaged position in which the piston is free to slide within the screw; and actuating elements configured to shift the piston from the engaged to the disengaged position upon electrical or mechanical failure of the actuator. The actuating elements include a key axially movable between the engaged and disengaged positions and having a locking section, configured to bias the locking dogs into interference with the abutting surface in the engaged position, and an unlocking section, configured to allow free sliding of the piston within the screw in the disengaged position. An anti-jamming device for operating a critical flight control surface.

A subsea electric actuator includes an electric motor and a telescopic drive connection from the motor to a drive unit that can be moved to and fro and converts rotary motion of the connection to linear motion of an actuating stem. A return spring is operable on the drive unit to urge the actuating stem towards a datum state. An electromagnetic latch is operative when set to maintain the drive unit in a predetermined position so as to decouple the action of the return spring whereby the stem can be advanced and retracted relative to the drive unit free from the action of the return spring. De-energization of the latch allows the return spring to operate on the drive unit to return the actuating stem to the datum state. Various forms of electromagnetic latches are described.