By Rafael Montero, Quality Manager, Avionyx

D-178C is a set of guidelines on what must be done to develop safety-critical airborne software, but it offers very little in explaining how to do it. One example is in the area of independence.DO-178C's glossary states that independence in verification tasks is achieved when the verification activity is performed by individual(s) who did not develop the items under verification, but it does not define the boundaries that should exist between the personnel that perform the various software development and verification activities.

Fortunately, additional guidance on this subject was provided from the Certification Authorities Software Team (CAST), an international group of certification and regulatory authority representatives from North and South America as well as Europe, in the form of a document called CAST-26 - Verification Independence. The guidance clarifies independence boundaries, including some of these major clarifications:

While CAST papers are not considered official guidance from any authorities, adherence to them generally will avoid independence compliance issues with your DER. And although independence is not required for all deliverables for all DO-178C assurance levels, some level of independence is strongly recommended as a good engineering practice to reduce defects and the cost of re-work and ultimately to improve safety.

For your copy of CAST-26 you may download it from the FAA website or directly for our website here Download