As DO-178B was updated to DO-178C it was decided  that the increasingly popular model-based development should be  made available to compliant appl i cations , and that they should be  addressed by  a supplement, DO-33 1 ,  “ Model-Based Development and Verification Supplement  to DO-178C and DO-278A ”.  

​ DO-331 takes the approach that  specification model s  or design models  take the place of high-level and  low - level requirements  respectively .  Textual requirements may   be linked  to models  upstream or downstream  ( Figure  1 ).  

Figure  1 :  Model Usage Examples ,  b ased on table MB.1.1 from RTCA DO-331  

Popular tools such as MathWorks ®  Simulink ® , IBM ®   Engineering Systems Design  Rhapsody ® , and ANSYS ®  SCADE can generate code automatically. DO-331  MB. 5.0 (Software  D evelopment  P rocesses) addresses traceability, model standards and more for both software requirements and design processes  where such tools are used .   MB. 5.3 (Software  C oding  P rocess) is  merely a cross-reference  the  equivalent  section in DO-178C ,  underlining the fact that best-practice c oding -related  process activities  still apply whether code is hand-coded based on a set of textual requirements, hand-coded based on design models, or auto-generated from a tool.    

​ Projects using auto - generated code almost always contain some hand - code  too , and often include legacy hand - coded components.   It is possible to apply different coding  standards  to  these different code subsets , such as  MISRA-C 2012 for hand - code, MISRA-C 2012  Appendix E  for auto -generated  code,  and a  custom coding standard for legacy code.    

​ DO-331 MB  6.0 (Software verification process)  expands on how best practice applies  to MBD , with DO-331  MB.6.8.2  (Model Simulation for Verification of Executable Object Code )  expanding upon  which verification objectives can be partially satisfied at the model level ,  and wh ich  must be performed at the target level.