These last two decades, many companies have grabbed the benefits of lean manufacturing in order to ease the flexibility of production workshops and enhance the global performance. However, when attempted to be implemented, the lean issue becomes less straightforward due to a lack of a clear understanding of the undertaken steps for achieving successful improvement. The main objective of this paper is to lead an analysis on the main inducers implying the aeronautic industry to commit in lean manufacturing practices, following by a first attempt to build up a strategic model providing gradual and relevant Lean implementation starting from VSM converging towards the Leanness achievement. A Leanness degree measuring the progression of Lean could provide a significant indicator to position the company in its global strategy and help evaluating the remaining efforts. Our findings are called to be applied in aeronautic companies to state their usefulness and get feedbacks from the direct practitioners.