Current design methods used within the aviation industry include the Systems Engineering (SE) methodology. Many products produced using this approach experience both scheduling and financial overruns resulting in a loss of value for the design. Recent developments in design have seen the introduction of the Value Driven Design (VDD) methodology which is an enhancement on the traditional SE approach. As this methodology is still in its infancy, many issues need to be clarified and developed before VDD can be fully implemented within the industry. One such issue is the development of subsystem value functions. To date, these local value functions only look at each individual subsystem in turn which results in an isolated design procedure as per SE. The main results from this work see the introduction of a Value Influence (VI) factor which enables interactions between these low level subsystems to be accounted for, thereby moving away from the current isolated approach. Further work will be required to fully develop these VI factors across multiple subsystems to ensure reliable, accurate calculations of value can be undertaken.