Abstract: A positive cable derailment sensing apparatus and method for use with pulley means having a cable carried thereby to detect derailment of the cable from the pulley means is disclosed. The sensing apparatus includes a flexible tendon secured to a low inertia component of the pulley means, usually a pivotally mounted yoke carrying a pair of pulleys, and secured to spring biasing means to bias the low inertia component for movement upon derailment of the cable from the pulleys. The flexible tendon normally extends from the pulleys to a remote position which is protected or shielded from adverse environmental conditions. Sensing means is located at the remote protected location and formed to sense movement of the flexible tendon and stop the advancement of the cable over the pulley means upon derailment. A switch construction particularly well suited for sensing the derailment of either side of the looped cable of the type found on chairlifts or the like is also disclosed.