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Aerospace Recommended Practice (ARP) 4754 Revision A (ARP4754A), Guidelines for Development of Civil Aircraft and Systems [1], and ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment [2], together describe a complex set of intertwining processes which comprehensively prioritize development activities for a product's systems based on their safety criticality. These processes work at specific levels of detail (aircraft and system) and interact with a set of processes at lower levels of detail (item) defined by Radio Technical Commission for Aeronautics (RTCA) standards. The aircraft and system development process (ARP4754A) supplies functions, requirements, and architectural definitions to the System Safety process (ARP4761), which in turn supplies Development Assurance Levels back to the development process and on to the RTCA processes.

The Systems Engineering (SE) “Vee” is generally recognized as one of the primary identifying features of Systems Engineering processes. While there are many specifications which include SE in their titles and show a version of the “Vee” in their process descriptions, there are other specifications which make no claim to be an SE standard but show a “Vee” describing the processes in the specification. There are also specifications which appear to be completely unrelated to SE but describe processes which are very much SE. This wide variety of documents points to the possibility of identifying the common core which composes SE (the soul of Systems Engineering). To search for the soul of SE, the words in two recognized SE standards along with the National Aeronautics and Space Administration (NASA) SE standard and multiple Federal Aviation Administration (FAA) standards have been analyzed for alignment of and differences between the models.

The Safety Assessment Process, defined by SAE ARP4761 and associated regulatory guidance, is described in the context of conventional, crewed civil aircraft. While this material has been used for decades to evaluate airplanes and rotorcraft, the evolution of technology challenges it. As new entrants venture into aviation, they bring perspectives, which may not clearly align to those conventional concepts. For those skilled in the art of aviation safety assessment, the approach to new technologies might appear straight forward. Such an individual might easily perceive the accommodations for unconventional applications. Once accommodations are made, and failure conditions are established and classified to those new architectures, the rest of the process is somewhat mechanical -they flow out of these conditions. However, the context of their experience betrays the reality of the process description in the ARP and guidance.