When testing gas turbine engines, a variety of flow parameters must be monitored. The precise measurement of total pressure and total temperature values is critical for evaluating the performance of the entire engine as well as individual engine components. Moreover, these parameters are used to define the control law and the engine health monitoring in an installed engine in operation conditions. The actual sensor design is often challenging due to the high temperatures and flow velocities within a gas turbine. This study's approach is based on separating the contributions of each component in the chain to the inaccuracy of the two systems, allowing for, first, a deeper understanding of the contributions of different parameters involved in defining the system's inaccuracy and, second, the formulation of inaccuracy forecast highlighted in a modern engine.