In modern industries, standard and well-known product development strategies require customization and dedicated methods to effectively conceive and manufacture complex products. The present research work aims at solving new challenges in product development targeting the aeronautical sector, specifically for the purpose of designing seat systems to be assembled and installed into commercial aircraft cabins. Basic Seat Assembly Concept Assessment (BSACA) design approach has been developed to assess seats assembly complexity in aircraft assembly line and to provide design guidelines in the early stages of product design. BSACA comprises four steps, starting from gathering the company’s knowledge to identify all the attributes characterizing the Seat Installation process. A series of scoring matrices is built, serving as a tool to translate the qualitative data gathered from design experts into quantitative values. Those matrices are used to create a software tool to help designers judge the goodness of new seat conceptual variants from an assembly viewpoint. Finally, the effectiveness of both the methodology and its stemming tool has been proven through a validation process carried out on four case studies. In essence, this research contributes a structured and rigorous framework to assess the ease and complexity of installing aircraft components, with a specific emphasis on seats, resulting in an improved assembly process of the whole aircraft.