Civil Airframe Structural Integrity—Some Probabilistic Aspects of Risk Assessment

Abstract

Fatigue is the mechanism of progressive damage which may ultimately limit the economic life of an airframe. However, there is an intrinsic variability in the life of nominally identical structures subjected to alternating loads. Currently, the uncertainty in the estimated fatigue lives is accounted for in design by applying ‘scatter factors’ to the results of full-scale fatigue tests or to deterministically calculated lives. An alternative approach is to perform a reliability analysis to ensure that the weaker members of an aircraft fleet will meet the design aims with a pre-defined level of reliability. This paper aims to develop and apply analytical models required to: determine the safe-life or inspection threshold for a given fleet size with a prescribed reliability and review and revise the inspection programme based on the results of in-service inspections.