Hello msbbarratt,
Excellent post !
In which case the spec was junk
In the case of Ariane501 somebody said the spec said that in case of double IRS failure stop the trajectory calculation... So that spec was not very smart !
And we often read on PPRuNe "It worked as designed".
The difficult for the IT analyst is to guess where something could be missing or wrong in the specification ! And we have to warn the people who is building the spec : "That could happen, do you want to accept that ?" because we know the hidden side of the system and architecture that the final boss is not aware with (like DeafOldFart suggesting to replace the B787 overflowed 32 bits integer by a 64 bits integer or modify the frequency
)
Let us hope it is the cheapest case for Boeing but probably it will not be the case as certifiers did jump over the bug too..
