Abstract: An actuator for a thrust reverser is disclosed which will prevent retraction of the thrust reverser door from its open, reverse thrust position should there be a malfunction in the locking system which locks the thrust reverser door in its closed forward thrust position. Upon deployment of the thrust reverser during a normal aircraft landing, should there be a malfunction in the thrust reverser door locking system, the actuator holds the thrust reverser doors in their opened positions so as to provide a positive, visual indication of such a system malfunction. The actuator has an internal device in the actuator head which, in cooperation with the control rod of the secondary mechanical locking system prevents hydraulic fluid from retracting the actuating piston and rod assembly from their extended positions and thereby prevents retraction of the thrust reverser door from the reverse thrust positions.