An electromechanical linear actuator includes a pneumomechanical back-up system to ensure extension of retractable landing gear for landing an aircraft. Structurally, the linear actuator includes a stator forming a channel for receiving a ball screw. Further, the actuator includes a ball screw housing forming a chamber for receiving the ball screw. Specifically, the ball screw and the housing are in threaded engagement to translate rotation of the ball screw into axial extension of the housing. To power electromechanical extension of the actuator, the ball screw is selectively engaged to a motor with a gear train. Importantly, fluid communication between the ball screw housing and a pressurized fluid is selectively provided by a valve. If electromechanical extension of the actuator fails, the gear train is disconnected from the ball screw and the pressurized fluid is introduced into the chamber to drive pneumomechanical extension.