Systems designers have to cope with the ever growing complexity of nowadays systems. This issue becomes dramatic in the aeronautics domain, due to the huge number of functions the systems have to support, the significant number of sub-system elements required to implement these functions and their inter-connections. Although requirements engineering is a good answer to the issue of system specification, as it enables the definition of a contract specifying the constraints the system architecture has to take into account, it does not scale very well when the size and the complexity of the systems increase significantly. Model Driven Engineering (MDE) approaches are currently used by software engineers to enhance software quality and increase capitalization in product line delivery for complex systems, but are not yet widely used at the system architecture level. As such, there is still a big gap between the system engineering world and the software engineering world, that is particularly obvious in requirement processing, leading to misreadings and misinterpretations of the system requirements by software engineers, with important consequences at the software architecture level. In this paper, we propose an MDE approach to address this issue at the system architecture level, contributing to bridge the gap between system and software architectures. In particular, we will describe an approach to deal with the expression of requirements in a MDE context, which relies on the notion of system conceptual modeling.