Inspection policies in service of fatigued aircraft structures

Abstract

Fatigue is one of the most important problems of aircraft arising from their nature as multiple-component structures, subjected to random dynamic loads. For guaranteeing safety, the structural life ceiling limits of the fleet aircraft are defined from three distinct approaches: Safe-Life, Fail-Safe, and Damage Tolerance approaches. The common objectives to define fleet aircraft lives by the three approaches are to ensure safety while at the same time reducing total ownership costs. In this paper, the damage tolerance approach is considered and the focus is on the inspection scheme with decreasing intervals between inspections. The paper proposes an analysis methodology to determine appropriate decreasing intervals between inspections of fatigue-sensitive aircraft structures (as alternative to constant intervals between inspections often used in practice), so that risk of catastrophic accident during flight is minimized. The suggested approach is unique and novel in that it allows one to utilize judiciously the results of earlier inspections of fatigued aircraft structures for the purpose of determining the time of the next inspection and estimating the values of several parameters involved in the problem that can be treated as uncertain. Using in-service damage data and taking into account safety risk and maintenance cost at the same time, the above approach has been proposed to assess the reliability of aircraft structures subject to fatigue damage. An illustrative example is given. © 2011 Springer Science+Business Media B.V.