Within the aviation regulatory system the current system safety assessment requirements have been around for 30 years or so and have made significant improvements in overall systems integrity, reliability and safety. However, these requirements are underpinned by some simple assumptions on system design whose continued use may no longer be regarded as appropriate given the highly integrated and complex systems in modern aircraft and the ever more integrated total aviation system that is currently being developed. This paper discusses some potential implications of this and questions what should we be considering for the future.