Abstract:

To address the flight safety risks posed by faults in aircraft control systems, a composite framework for fault risk assessment based on IRPN was proposed. This framework comprehensively considered four key risk factors: fault probability, severity, detectability, and risk damping. First, system fault modes were deduced bidirectionally using FMECA-FTA method. Second, human and environmental factors were incorporated, and a Bayesian network approach was employed to construct a hybrid probability model for calculating fault probabilities. Third, fault severity was categorized into three evaluation parameters, which were comprehensively assessed using the Analytic Hierarchy Process and Fuzzy Comprehensive Evaluation methods. Next, utilizing resources such as pilot quick reference manuals and aircraft type design manuals, a criterion-based reasoning method was applied to establish detectability scoring criteria, allowing for a more scientific evaluation of fault mode detectability levels. Finally, the FRAM was introduced to define risk damping coefficients, characterizing the propagation of risk during the evolution of fault risks. The computational validation was carried out with the case of jamming failure mode of aircraft flap seam wing actuation system. The research results show that its IRPN assessment result is 158, which is in perfect agreement with the actual operation. The validity and accuracy of the failure composite risk index calculated by the IRPN composite risk assessment framework are confirmed by the failure mode example simulation and the real verification of unsafe events.

Key words: aircraft control systems, fault risk assessment, hybrid probability model, improved risk priority number (IRPN), failure mode, effects and criticality analysis(FMECA)-fault tree analysis(FTA), functional resonance analysis method (FRAM)