Abstract: An actuator for raising and lowering aircraft landing gear in accordance with the extended and retracted state of the actuator includes a cylindrical casing, a piston assembly slidable along the axis of the casing, a fluid pressure source, a sealed chamber containing gas, a free piston forced by fluid pressure along the casing axis to compress the gas, latching devices for locking the piston assembly to the casing, a locking mechanism for holding the free piston in position on the pressure tube when the gas is compressed and hydraulic passages interconnecting the chamber containing pressurized gas and the space containing pressurized hydraulic fluid. A mechanism is provided for initiating automatic retraction of the actuator due to the effect of a self-contained perpetual source of compressed gas if hydraulic pressure is lost. A compression spring stores a force while the piston assembly moves between retracted and extended positions.