The progressive industrialisation of composite-built aircraft is putting manufacturing engineers on a steep learning curve. An opportunity exists to use knowledge management tools to capture, share and reuse knowledge over multiple aircraft programs and maintain the constant flow of learning gained during aircraft program delivery. This article reports on research to develop a knowledge-based cost modelling capability for composite part concept evaluation. The approach integrates a knowledge management environment with a process-based cost estimation tool encoded in very large spreadsheets. To achieve this, the complexity of the cost model is managed by modularising it into simple, re-useable components. The knowledge management environment is then used to manage the knowledge life cycle, knowledge exploitation and knowledge visibility of those components. The result is a flexible cost modelling tool composed of traceable, verifiable and reliable knowledge elements that provides through-life knowledge support for cost engineering. Validation is achieved through functional application of the solution for composite wing top cover cost modelling.