Purpose -Maintenance disassembly that involves separating failed components from an assembly or system plays a vital role in line maintenance of civil aircraft, and it is necessary to have an effective and optimal sequence planning in order to reduce time and cost in maintenance. The purpose of the paper is to develop a more effective disassembly sequence planning method for maintenance of large equipment including civil aircraft systems. Design/methodology/approach -The methodology involves the following steps: a component-fastener graph is built to describe the equipment in terms of classifying components into two categories that are functional components and fasteners; interference matrix is developed to determine the removable component, and a disassembly sequence planning of functional components is proposed based on Dijkstra's algorithm; the disassembly sequence planning including fasteners is presented based on particle swarm optimization. Findings -An application case, which takes the nose landing gear system of a regional jet as a study object, shows that the disassembly sequence planning method proposed in the paper can reduce the calculation complexity greatly, and its effectiveness is greater than that of a genetic algorithmbased method, in most situations. Practical implications -The method proposed herein can acquire the optimal maintenance disassembly sequence, which can reduce the cost and time for maintenance of large equipment. Originality/value -A novel and effective disassembly sequence planning solution for maintenance of large equipment is presented, which can be applied to the line maintenance of civil aircraft.

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Background: In the interest of improving aircraft performance, studies have highlighted the benefits of Box wing configurations over conventional cantilever aircraft configuration. Generally, the greater an aircraft's average thickness to chord ratio (τ), the lower the structural weight as well as volumetric capacity for fuel. On the other hand, the lower the ., the greater the drag reduction. A review of patents related to the Box-wing aircraft was carried out. While methodologies for optimizing wing thickness of conventional aircrafts have been studied extensively, limited research work exist on the methodology for optimizing the wing thickness to chord ratio of the Box wing aircraft configurations. Methods: To address this gap, in this work, a two stage optimization methodology based on gradient search algorithm and regression analysis was implemented for the optimization of Box wing aircrafts wing thickness to chord ratio. The first stage involved optimizing the All Up Mass (AUM), Direct Operating Cost (DOC) and Zero Lift Drag Coefficients (CDO), with respect to the aft and fore sweep angle for some selected τ values. At the second stage, a suitability function (γ) was optimized with respect to the aft and fore sweep angle for some selected τ values. A comparative study was further carried out using the proposed methodology on similar size cantilever wing aircraft. Results: From the result, an optimal τ value was reached. Also the τ value for the cantilever aircraft found based on the proposed methodology was similar to the true τ value of the adopted aircraft, thereby validating the methodology. Conclusion: Based on the optimal τ value reached from this work, the Box wing aircraft are suitable for thin airfoils.