Abstract
<jats:p>Objectives: This study develops a certification-informed analytical framework for the preliminary structural design of an under-wing box-beam engine pylon representative of a twin-engine wide-body civil aircraft. The objective is to link airworthiness-derived loading requirements, engine–pylon reactions, structural architecture and geometry-based mass assessment within a traceable early-design workflow. Methods: Three aircraft mass states, five characteristic speeds and nine altitude conditions define the baseline design space. Gust, gyroscopic, engine failure, engine seizure, and emergency loading are evaluated to establish six-component reaction envelopes. These loads are transferred through an idealised closed box-beam representation to derive internal shear-force, bending-moment and torsional distributions and to support preliminary structural sizing of skins, ribs, stiffeners, spar caps and attachment lugs. Results: The final configuration contains 12 ribs and transitions from integral blade stiffeners in the central box to four L-section spar caps in geometrically constrained tapered regions. The CAD-based structural mass is approximately 596 kg per pylon, with the Ti-6Al-4V primary structure contributing approximately 85%. Conclusions: The methodology provides a transparent analytical route from certification-informed loading to preliminary structural architecture and mass assessment. No finite-element stress, displacement or buckling results are used as validation evidence; higher-fidelity numerical and experimental verification remains necessary.</jats:p>