re: Perfect Software
ams6110: I'm not a commercial pilot but I do have 25+ years in software. It's not so much "wishful thinking" about perfect software but the cost of attaining it. The Space Shuttle flight control software team was one group that was famous for attaining near zero defects, but they did so with incredible rigour and an associated slow pace.
Can anyone shed some light on the language used in the GCU's system? Was it Ada or C/C++? Regardless, it's pretty common to do "what happens when this value hits its maximum + 1" testing. Even in simple web systems I often do that in unit tests to verify that nothing breaks in an unexpected way.
The difference in this case is probably that it's an internal counter rather than a parameter being passed about. A parameter would probably be subjected to boundary value tests, but perhaps not a global counter. There are also tools for what's called "fuzz testing" that will inject invalid values to catch just these sorts of problems. Again, though, that may have been done but just not in the right place.
One hope I do have, though, is that Boeing treats this like a mechanical issue and does proper root cause analysis and deals with the human aspects as much as the technical ones. That doesn't happen very often at all in the software world.