A dual redundant control system whose fault-tolerant policy is capable of removing the failed controller is proposed. The heuristics of detecting failures of a controller and changing the time weight take the form of a set of linguistic decision rules in fuzzy logic. This detection method based on performance measure enables the detection of a failed controller without relying on mathematical model and failure assumptions. It can handle gradually degrading failures as well as catastrophic failures by introducing the concept of failure measure and time weight. The failed controller is smoothly removed by reducing the time weight of the failed controller.