Purpose of this Order.

a. We've written this order to supplement RTCA/DO-254, and give you guidance for approving both simple and complex custom micro-coded components. This guidance applies to airborne systems and equipment, and the airborne electronic hardware of those systems when you work in a certification project (type, supplemental, amended, and amended supplemental) or technical standard order authorization. This order accepts RTCA/DO-254 as the means by which an applicant can seek FAA approval. If an applicant proposes another means, including achieving acceptable design assurance for these components by using verification and/or architectural strategies at the system or equipment level, we may need to develop more guidance (such as issue papers) on a project-byproject basis.

b. If an applicant follows RTCA/DO-254 for level D components, we don't need to review the life cycle data. However, we will review it if the applicant chooses to use their existing design assurance practices, as allowed by Advisory Circular (AC) 20-152, RTCA, Inc., Document RTCA/DO- 254, Design Assurance Guidance For Airborne Electronic Hardware, Paragraph 1.b. Refer to FAA part- specific policy for exceptions.