Why don't voice radio communications use FM?

Bob Noel writes:

There are versions of VxWorks that are certifiable to DO-178B level A.
Kind of hard to do that while allowing full run of the memory.

Why?

um, not always. the complexity of the OS could dominate the complexity
of the app, especially if the OS provides protection for the app (e.g.,
partitioning).

In mission-critical systems, all of the software works as an
integrated whole; you don't just load arbitrary code off a CD and run
it. If you are running untrustworthy code, you're also running
uncertified/unvalidated code, which is dangerous.

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