scope:

PURPOSE.

This notice provides guidelines to Aircraft Certification Office (ACO) engineers and Designated Engineering Representatives (DER) regarding the application of RTCA/DO- 178B, "Software Considerations in Airborne Systems and Equipment Certification," to previously developed software (PDS) that has been categorized to contribute to at most a minor failure condition on the aircraft. Advisory Circular (AC) 20-1 15B recognizes DO-178B as an acceptable means of compliance for the evaluation of software in airborne systems and equipment. DO-178B assigns a software level of D to any software that can cause or contribute to no more than a minor aircraft failure condition. However, the application of the objectives associated with Level D software are frequently misinterpreted, especially when applied to software that was not originally approved using DO-178B (i-e., PDS). This notice should be used to apply DO-178B to PDS that is categorized as Level D.