Enhancing Airworthiness Through Dynamic System Reliability Modeling For Complex Military Aircraft Systems

摘要

In System Reliability one constructs a "System" model from component models. In other words in system reliability analysis we are concerned with the construction of a model (life distribution) that represents the times-to-failure of the entire system based on the life distributions of the components, subassemblies and/or assemblies ("black boxes") from which it is composed. A system is a collection of components, subsystems and/or assemblies arranged to a specific design in order to achieve desired functions with acceptable performance and reliability. The types of components, their quantities, their qualities and the manner in which they are arranged within the system have a direct effect on the system's reliability. To accomplish this, in addition to the reliability of the components, the relationship between these components is also considered and decisions as to the choice of components can be made to improve or optimize the overall system reliability, maintainability and/or availability. This reliability relationship is usually expressed using logic diagrams, such as Reliability Block Diagrams (RBD) and/or Fault Trees. The reliability of components varies depending on the failure rates for the different types of components, e.g. electrical, mechanical, etc. For instance, the typical bathtub curve has been used for electronic components with constant failure rates used after initial burn in until wear-out. Mechanical components and structural components experience aging over time, so the constant failure rate doesn't apply. In addition, software failure rates have almost a continuing burn-in rate as changes and up-dates are made. Finally, the reliability of the human, or "liveware", has only been subjected to limited reliability analysis. This paper will describe an overall systems approach for system safety and airworthiness. It will address system reliability of complex systems using a safety case or target level safety approach. It will introduce dynamic system modeling techniques, such as stochastic petri nets, that can account for gaining and not constant failure rates