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A Dynamic Fault Tree Approach for Time-Dependent Logical Modeling of Autonomous Flight Systems

Cobham Mission Systems Inc-John Wang
Published 2019-03-19 by SAE International in United States
This paper addresses the urgent need for adequate methodologies to use in analyzing autonomous flight systems, including Unmanned Aircraft. These systems are inherently dynamic and require analysis that is explicitly time dependent. Autonomous flight systems are becoming more commonly used, especially for Part 23 aircraft including Business (Corporate) and Regional Jets or Unmanned Aircraft deployed in hazardous environment/situation. Such systems are expected to make their own decisions under uncertain conditions caused by potential system structure changes when entering a new flight phase or switching to a new system configuration due to system degradation or failure(s) [1]. This paper highlights significant modeling errors that can arise in analyzing dynamic scenarios where these time dependencies are ignored. Model-based solutions are provided by incorporating a time-dependent algebraic formalism into Fault Tree Analysis (FTA) and Dependency Diagram (DD) with updated descriptions in SAE ARP4761A and ARP4754B (Note: These are currently under development). A Dynamic Goal Tree (or alternatively, a Dynamic Dependency Diagram) provides an effective implementation of the time-dependent logic for dynamic system analysis analyzing autonomous flight systems which…
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Complexity as a Measure of the Difficulty of System Diagnosis in Next Generation Aircraft Health Monitoring System

Cobham Mission Systems Inc-John Wang
Published 2019-03-19 by SAE International in United States
To develop the Next Generation Aircraft Health Monitoring System (NGAHMS), complexity as a measure of the difficulty of diagnosis, or troubleshooting, of a system is explored in this paper. The results presented can be applied to significantly improve safety and human factor design as an important as aspect of risk engineering and management. This is accomplished in system architecture design by quantifying the system structure’s effect on system complexity as well as the number of components which make up the system. For developing the NGAHMS to make flying even safer, more fuel efficient, and more predictable, model-based safety assessment methods such as Fault Tree Analysis (FTA) and Dependency Diagram (DD) with updated descriptions in SAE ARP4761A and ARP4754B can be used to minimize the average number of airborne inspections to find the Minimal Cut Set (MCS) causing an aircraft failure. Since, based on previous research, this average number of airborne inspections is proven to be lower-bounded by the entropy of cut set importance, the system complexity measure can be used to efficiently estimate how difficult…
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