CAST-15
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CAST-15, Merging High-Level and Low-Level Requirements is a Certification Authorities Software Team (CAST) Position Paper. It is an FAA publication that "does not constitute official policy or guidance from any of the authorities", but is provided to applicants for software and hardware certification for educational and informational purposes only.
Abbreviation | CAST-15 |
---|---|
Year started | 2003 |
Organization | Certification Authorities Software Team |
Domain | Avionics, type certification |
As established by the FAA advisory circular AC 20-115, the RTCA publication DO-178B/C defines an acceptable means of certification of airworthy software. Unique among development standards, DO-178B introduced a distinction between High-Level Requirements and Low-Level Requirements as formal products of software requirements analysis and design when developing airworthy software.[1][2][3]
DO-17B/C assigned different sets of objectives to these two levels of requirements. To accomplish compliance, the Applicant needs to fulfill both sets of objectives with their requirements. However, under narrow conditions, that standard's guidance permits combination of these two levels into just one level of requirements, but warns against the practice in general.[4]
This position paper is concerned with observed misuse of this guidance; some applicants were combining High-Level and Low-Level Requirements for "simple" products, but were not accomplishing all of the related objectives for both levels of requirements.[5]
This position paper is also an example of Certification Authorities using their "what" versus "how" distinction[6] between high-level and low-level requirements[7][8][9] that DO-178B/C does not clearly explain.