Theoretical and practical investigation of complex systems has become important in several fields of technical and social sciences. One of the most important questions is the sensitivity of these systems. The main aim of this paper is to show adaptation of mathematical diagnostic methodology of aircraft systems and gas turbine engines to determine sensitivity of reliability of finite Systems with Complex Interconnections. These proposed analogous methods are named Linear Sensitivity Model of system reliability and Linear Sensitivity Model of System Unreliability. The paper shows the proposed methods theoretically and their applicability to investigate Systems with Complex Interconnections sensitivity by a simple example.