Methodology for an integrated definition of a system and its subsystems: the case-study of an airplane and its subsystems

A modern airplane is without any doubts one of the clearest and most convincing example of “complex system”. A modern airplane consists in fact of various types of elements of different technologies (structures, mechanics, electric, electronics, fluids, etc.). Each element has specific tasks to perform and all elements are harmonically integrated to constitute the whole system. Moreover the airplane is a particularly critical system because of quite obvious safety reasons, because of the relevance of its mission, because of high costs and eventually because of its long Life Cycle. Figure 1 shows an example of a modern transport aircraft. Let us consider the case of such an airplane, whose mission statement sounds like: “To transport in flight a certain payload from point A to point B”. At a first glance the airplane can be seen as a single entity able to perform a well defined function but, getting more into the details, the airplane appears as consisting of various parts, all harmonically integrated and concurrently working to accomplish the same mission. For instance, taking into account Figure 1, different items, like the wing, the fuselage, the horizontal and vertical tails, the engine nacelles with propellers and the wheels of the landing gear (when the aircraft is on ground), can be easily individuated. By looking at the whole aircraft more into the details, other items can be identified or at least imagined, like the structural elements, the engines and many mechanical, electronic and fluidic installations, referable to the numerous and various technologies present onboard the aircraft.