DO-178B
| Latest version | December 1, 1992 |
|---|---|
| Organization | |
| Domain | Aviation |
| Abbreviation |
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DO-178B, Software Considerations in Airborne Systems and Equipment Certification is a guideline dealing with the safety of safety-critical software used in certain airborne systems. Although technically a guideline, it is (or was) a de facto standard for developing avionics software systems.
The FAA applies DO-178B as the document it uses for guidance to determine if the software will perform reliably in an airborne environment, when specified by the Technical Standard Order (TSO) for which certification is sought. In the United States, the introduction of TSOs into the airworthiness certification process, and by extension DO-178B, is explicitly established in Title 14: Aeronautics and Space of the Code of Federal Regulations (CFR), also known as the Federal Aviation Regulations, Part 21, Subpart O.
It was jointly developed by the safety-critical working group RTCA SC-167 of RTCA and WG-12 of EUROCAE. RTCA published the document as RTCA/DO-178B, while EUROCAE published the document as ED-12B.
The Software Level, also known as the Design Assurance Level (DAL) or also '"Item Development Assurance Level"' (IDAL)is determined from the safety assessment process and hazard analysis by examining the effects of a failure condition in the system. The failure conditions are categorized by their effects on the aircraft, crew, and passengers.
DO-178B alone is not intended to guarantee software safety aspects. Safety attributes in the design and as implemented as functionality must receive additional mandatory system safety tasks to drive and show objective evidence of meeting explicit safety requirements. Typically IEEE STD-1228-1994 Software Safety Plans are allocated and software safety analyses tasks are accomplished in sequential steps (requirements analysis, top level design analysis, detailed design analysis, code level analysis, test analysis and change analysis). These software safety tasks and artifacts are integral supporting parts of the process for hazard severity and DAL determination to be documented in system safety assessments (SSA). The certification authorities require and DO-178B specifies the correct DAL be established using these comprehensive analyses methods to establish the software level A-E. Any software that commands, controls, and monitors safety-critical functions should receive the highest DAL - Level A. It is the software safety analyses that drive the system safety assessments that determine the DAL that drives the appropriate level of rigor in DO-178B. The system safety assessments combined with methods such as SAE ARP 4754A determine the after mitigation DAL and may allow reduction of the DO-178B software level objectives to be satisfied if redundancy, design safety features and other architectural forms of hazard mitigation are in requirements driven by the safety analyses. Therefore, DO-178B central theme is design assurance and verification after the prerequisite safety requirements have been established.
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