In avionics domain, currently most engineering efforts and costs come from integration, verification and validation activities. Each error found on requirements during product verification or validation requires a full engineering cycle to manage the change: impact analysis, design, realization, integration, verification and validation again. Hence, ensuring early and continuous validation of requirements in the engineering life cycle, becomes more and more crucial. In this paper, a Model-Based Systems Engineering (MBSE) approach is proposed. The proposed approach relies on SysML models and is composed of modelling tasks to capture requirements and to structure functional interfaces and functions. This approach has been applied in the frame of SAE ARP4754A aerospace recommended practices. This paper also provides feedback about the application of the proposed approach on an industrial avionic case study known as the Onboard Maintenance System by a team mainly used to document centric approach until recently. The feedback concerns the practical use of models to support functional part of the following processes: requirements capture, requirements validation, and top-level part of development of system architecture. After presenting the pilot case, results are given and discussed on several points: the lessons learned during and after application of the MBSE approach to identify use cases, to define black box scenarios, and to build the top-level functional architecture. Comments about the approach are given, e.g. use cases granularity, modelling stop criterion, communication between systems. Then, measured advantages and drawbacks of this modelling approach are discussed. The paper finally describes the challenges identified for wider adoption in the company and the remaining points of attention when extending the approach on a larger project.