The contemporary debate on the need for the civil aeronautical industry to reconcile its global warming impact and the continuous air traffic growth is gaining in prominence. While solutions exist to tackle different aspects of this complex problem individually, the core of the response lies in rethinking the conventional aeroplane architecture in order to reach new energy efficiency optima. This paper presents a function-to-form framework used for describing different aspects of architectural design of an aeroplane as technological system. Firstly, a brief overview of different existing ways to improve aeroplane architectures is given. With that background, a preliminary definition of multi-level system composition of an aeroplane is presented. A physics-based framework is then correlated to the Functional, Behavioural, Structural and Experiential requirement framework, in order to characterise the different physical phenomena experienced by an aeroplane for a single operating point. These provide basis for definition of a qualitative Figure of merit dubbed Integration Potential of an architecture, which serves as proxy for describing function-to-form mapping of aeroplane system architectures. Using both the historical, contemporary and projected tendencies of aeroplane technology advances, existence of an asymptotic limit of this parameter is inferred. This limit arguably indicates the extent to which it could still be possible to go in search for energy efficiency gains by virtue of system architecture design.