Abstract: The servomotor outputs of two substantially identical servo channels, are connected through a differential mechanism to position an attitude control surface of an aircraft in response to common or separate command signals applied to the respective channels. The dual channels are continuously monitored in such a manner that if the velocities and accelerations of the two servomotor outputs do not track each other within predetermined ratio limits, appropriate servo brakes will clamp the output of the servomotor with the highest acceleration, or the failed channel. The rapidity with which the failed channel is detected and the servo brakes applied assures that essentially no control surface motion occurs and hence no attitude or flight path transients are evident by reason of the failure. Clamping of the failed servomotor, moreover, assures that the remaining servo channel may remain operative.