Research On Safety Analysis Method Of Aircraft Brake System Based On MB-STPA

The aircraft braking system is a typical complex system.The relationships of the risk factors are not simple linear causality,but complex non-linear interactions,which put forward new requirements for hazard identification methods.At the same time,the operation phase is affected by a variety of uncertain factors and system performance degradation.The control operations determined during the design may not guarantee the continuous safe operation,so it is necessary to conduct a risk assessment at the operational phase.For the operational unsafe events at the new situation,more scientific and effective methods should be adopted to identify risk factors,assesse and monitor the risk level to ensure the ongoing safety.To solve this problem,the System Theory Process Analysis method(STPA)and Model-Based Safety Simulation Analysis(MBSSA)are deeply integrated to form a new system safety analysis method,named MB-STPA.Aiming at the problem that the STPA method cannot be quantitatively evaluated,the MBSSA method is introduced to deepen the analysis results of the STPA method.For the unsafe event,the STPA was firstly used to construct the control-feedback structure diagram of the system to identify the unsafe factors,including unsafe control activities and their causes.Then,under the guidance of the Model-Based Safety Simulation Analysis,the system and the fault model were established to analyze the impact of the fault on the control activities and the control activities on the safety of the system by simulating the control activities and fault.Next,in order to further quantify the uncertainty of the risk,the operating parameters obtained from the model simulation were as the data samples.And the Monte-Carlo method and the improved multiparameter Copula extreme value theory were used to construct the risk probability assessment and prediction model,which could determine the risk level of the unsafe events and the overall of the system and predict the number of remaining flights during the faulty operations.Finally,the effective risk control measures could be formulated based on the results of sensitivity analysis.To verify the feasibility and effectiveness of the MB-STPA,the aircraft brake system was taken as an example to compare the results with the FTA.The risk factors of operational unsafe events can be effectively identified by the system safety analysis method,which is based on the system theory and model simulation;The risk probability assessment model can be used to evaluate the risk of the complex system and its unsafe events,which has some guiding significance for fault flight and design improvement in the operational phase.