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Understanding DO-254 and Solutions to Facilitate Compliance wwww.mentor.com 3 WHEN DID IT BECOME POLICY? DO-254 was written to apply to all levels of hardware design and finalized as an industry document in 2000. Eventually, the FAA invoked DO-254 as policy with Advisory Circular (AC) 20-152, which changed the scoping. This policy document, issued on June 30, 2005, states that "This AC recognizes the guidance in RTCA/ DO-254 applies specifically to complex custom micro-coded components with hardware design assurance levels of A, B, and C, such as ASICs, PLDs, and FPGAs." Prior to this, the FAA and airframe integrators had used compliance to similar requirements that were defined by special documents such as Issue Papers (IPs) or Certification Review Items (CRIs) for specific aircraft programs. In some cases this meant following DO-178B, which is the complementary standard for software design assurance. Today IPs and CRIs still do influence how DO-254 must be complied with on aircraft programs. The interpretation of DO-254 has been clarified and influenced by two FAA documents: Order 8110-105 and the "Conducting Airborne Electronic Hardware Design Reviews," otherwise known as the Job Aid. Order 8110- 105 clarifies a number of ambiguities in the original invocation of DO-254 from AC 20-152. The Job Aid is an internal FAA document used by DO-254 auditors as they perform their "Certification Liaison" tasks. Both of the documents are public and can be found on the FAA web site (www.faa.gov). Figure 1 shows DO-254 as a means of compliance to the CFRs, along with the other types of policy documents that influence its interpretation. Figure 1. Regulation, DO-254, and Related Policy It's important to have a big picture understanding of why DO-254 compliance is necessary and all of the related policy documents and regulations that influence its interpretation. Thus, complying with DO-254 is not as simple as reading the document and following what it says. The document itself was written with a different scoping than it is currently applied, and subsequent policy documents and opinions have influenced its interpretation and today's common compliance practices.

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