Abstarct: An fault is an integral part of any industrial system. In order to achieve a high level of safety in the system, as well as to improve the performance and reliability of the control processes, it is important to recognize and isolate the fault. In this thesis, the error detection is performed with the help of designing an adaptive threshold baxsed on parity equations. The reason for applying the adaptive threshold baxsed on parity equations in comparison with the normal threshold is that in the design of the normal threshold by defining the threshold level for the remaining amount, in most cases the residuals that are obtained are much smaller than the threshold, and the system can not detect or fix these faults, which during long time cause failures and disruptions in the system. Due to this, we use the adaptive threshold baxsed on parity equations. This design features the ability to detect near-zero faults and isolate other signals in the output. In the simulation the linear model of the aircraft pitch is considered. In order to evaluate the proposed method, sensor and actuator faults are applied to the system. The results are examined in different conditions. In each case, the simulations for the fault estimation are considered with a threshold design and no threshold. The results show that in this design, the accuracy of fault detection has been increased and the isolation of very small faults has been well done.