Abstarct: Fault detection and diagnosis form one of the most important concerns in industrial processes. Timely fault detection and correction can contribute to the prevention of fault progression and further damage. Acquisition of accurate fault information only through fault detection is not easy due to the effects of the model uncertainties, noises, and disturbances. Therefore, more accurate fault information can be obtained through fault estimation. One of the conventional fault detection methods involves the use of observers. The research topic is the actuator fault detection in a Three-axis Gyro-stabilized camera mount (remote sensing system) with disturbanc. First, the