Research On Application Of Time-limited Dispatch Technology In FADEC System

Aeroengine control system is the core of engine safety control.In ccar33.28,airworthiness authorities strictly limit the frequency of loss of engine thrust control events caused by the aeroengine control system.For transport aircraft meeting the requirements of ccar25,ccar33.28 stipulates that the loss rate of thrust control caused by a single engine shall not be higher than 10-5 / FH.Based on the in-depth study of the regulations on time limited dispatch technology in arp5107 and the FAA policy letter ane-1993-33.28tld-r1,the application process of time limited dispatch technology is summarized.In view of the difficulties and future trends in the application of time limited dispatch technology,the following research is carried out:First,the fault tree analysis of the actual FADEC system is carried out,and the basic failure rate data required for TLD analysis and the system lotc after failure are obtained.For the mature system,the loss rate of thrust control is kept unchanged as the constraint condition,and the system mtbr is taken as the optimization objective.By analyzing the relationship between the short-time dispatch interval and mtbr,the method to determine the short-time dispatch interval is given.Secondly,because single fault mm is used for TLD analysis,it is necessary to analyze the accuracy of single fault mm according to the requirements of policy letter.By analyzing the principle of time limited dispatch method,the source of precision error is obtained,and the best precision analysis method is obtained through simplified model and numerical analysis.The analysis shows that the accuracy of single fault MM model is affected by dispatch interval and system complexity.The longer the dispatch interval is,the more complex the system is and the lower the model accuracy is.Then,according to the conclusion that the increase of system complexity in accuracy analysis method will increase model error,it is not enough to rely on Markov model analysis only for the increasingly complex trend of Aeroengine Design in order to meet more functions.In order to solve this problem and quantify the impact of maintenance strategy on lotc rate,TLD analysis is carried out by using improved Monte Carlo simulation model.Compared with Markov model,the result of Monte Carlo simulation is correct.The results show that under different maintenance strategies,the difference of maintenance interval is 11.99%,which indicates that different maintenance strategies have great influence on the analysis results.Finally,in order to simplify the analysis of time limited dispatch and improve the efficiency,a time limited dispatch auxiliary analysis system is developed.The system integrates the functions of time limited dispatch analysis,quantitative expression of dispatch interval relationship,Monte Carlo simulation of time limited dispatch,and it can adapt to different FADEC systems.