By Bill StClair, Director, LDRA Certification Services

Welcome to my inaugural edition of a quarterly series of RTCA blog posts, featured as part of the LDRA blog. These RTCA blog posts will consider plans and activities pertaining to safety critical software (ED-80C/DO-178C, et al) and airborne electronic hardware (ED 21/DO-254) standards. The series will quickly expand to include other impactful standards such as Software Tool Qualification Considerations ED-215/DO-330, and ED-124/DO-297, Integrated Modular Avionics Development Guidance and Certification Considerations.

This first RTCA blog post will focus on the long overdue revision of ED-21/DO-254. The Working Group WG-128 and Special Committee SC-243 will be the organizing bodies for EUROCAE ED-80(A) and RTCA DO-254A joint standard. The reopening of ED-80/DO-254 kicked off on February 26/27 at Joby Aero, Inc, in Santa Cruz, CA USA. Attendees are captured in this pic:

ED-80A/DO-254A Revision Principles

The principals that guide the ED-80/DO-254 revisions are similar in many ways to those that were applicable to WG- 80/SC-205 in the development of ED-12/DO-178C.

• Keep the standard objective-oriented (as was heavily emphasized in DO-178C). Do not compromise the current understanding of the standard (keep the same philosophy).
• Merge and maintain safety aspects and objectives of A(M)C 20-152A, and predecessor guidance material.
• Ensure it will be easy to identify objectives for devices, boards, LRUs.
• When introduced, new objectives should contribute to the safety of equipment.
• Check for consistency of safety aspects with ARP4754B (for verification, for example).
• Keep ED-80/ DO-254 technology independent as much as possible.
• Reuse best practices from other standards (including the use of common definitions) and harmonize definitions across standards.
• Avoid significant changes to current structure.
• Minimize impact on current development.
• Limit component management to Design Assurance aspects, allowing other standards to take precedence for other considerations.
• Minimize the introduction of prescriptive additional guidance. Create separate documents rather than compromise the structure of ED-80/DO-254.

In general, the aim is to achieve the harmonization and alignment of activities and dependencies between hardware, software, system, and safety, and to address overlapping activities between them. This includes the clarification of the relationship between ED-80/DO-254, and ARP4754B and ARP4761A.

WG-80/SC-205 will also consider a rewrite to:

• Replace references to Functional Failure Path Analysis (FFPA) in DO-254 Appendix B with references to ARP4761A (and ARP4754B) as appropriate.
• Replace hardware safety assessment with hardware contributions to, and outputs from, the system safety types of analyses.
• Address the interfaces between system, safety and software.
• Maintain sections for the interfaces to the other subjects.
• Minimize duplication of content from ARP4754 and ARP4761 within ED-80/DO-254.

Level of Effort

The intent is to keep a reasonable target (2-3 years) for the first update (revision A of ED-80/DO-254. Then, a dynamic process should be launched to propose further revisions. To maintain that target, the members of the Committee agree to park subjects when consensus is not able to be reached. That said, the committee has deferred addressing cybersecurity considerations to a future revision…is that a stretch?

References

ED-80 / DO-254 Design Assurance Guidance for Airborne Electronic Hardware
A(M)C 20-152A Development Assurance for Airborne Electronic Hardware (AEH)
AC 00-72 Best Practices for Airborne Electronic Hardware Design Assurance
ED-215/DO-330, Software Tool Qualification Considerations
ED-80C/DO-178C Software Considerations in Airborne Systems and Equipment Certification
ED-124/DO-297 – Integrated Modular Avionics (IMA) Development Guidance and Certification Considerations
SAE ARP4754B/ED-79B Guidelines for Development of Civil Aircraft and Systems
SAE ARP4761B/ED-145B Guidelines for Conducting the Safety Assessment Process on Civil Aircraft, Systems, and Equipment
RTCA/EUROCAE committee SC205/WG-71 (aka, “DO-178C committee”)
Working Group WG-128/Special Committee SC-243 (aka, “DO-254 committee”)