Time-limited dispatch technology (TLD) is not only to meet the practical needs of civil aviation to ensure profitability on the basis of safety, but also an important airworthiness verification link of aviation engines. The source and basis of TLD analysis are briefly introduced. At the same time, based on the reliability model of FADEC system of a certain engine, MM and MC methods are used to analyze and derive the average LOTC formula of the system under single fault state and multiple fault state by means of theoretical equation and numerical analysis. By comparing and analyzing the error determination of the two methods under the condition of double fault, the MC method can effectively solve the high-dimensional state space explosion problem in the MM method within the acceptable error range under the condition of multiple faults, the application flow of the simulation analysis method in TLD is determined, and the rationality and applicability of the MC method under the condition of multiple faults is verified. On the basis of simulation analysis, the influence of reliability model optimization iteration on the system is discussed through system reliability distribution analysis, so as to ensure that the system can run in a safe and reliable environment.