I think many people fail to understand that safety critical software can't rely on "highly competent programmers". No matter how competent, programmers can't be trusted to write safety critical code.

Safety critical software is all about the process and organization. The process must be so good that you can hire total newbie to write code and none of his sloppy work would get into the final product.

What you need is software engineer who writes 20 lines of code and can then justify each of the 100 lines in a resulting spreadsheet that is full MC/DC code coverage in processor instruction level. Then you need two testing engineers who can do the same for code that others have written. Then you need everyone to go trough every change, justify them, rewrite tests and provide reports.