Originally Posted by
DozyWannabe
Said by whom?
And no one was talking about software attaining perfection. Merely that the probability of two completely separate pieces of imperfect software prohibited from sharing any common logic coming up with the same computational error is extremely remote.
This is (roughly) the main hypothesis behind NVP (n-version programming). Knight & Leveson famously claimed to have disproved this experimentally
http://sunnyday.mit.edu/critics.pdf. Specifically, they claimed that errors
were correlated between independently developed versions of the software. This might be counterintuitive, but it wouldn't be the first counterintuitive result in the history of science.
Also worth noting that Boeing dropped NVP when developing the 777 flight control software. They engaged a single contractor for triplex development (three separate teams with "chinese walls" between), but changed to one team part way through development, apparently because the teams were asking such similar questions about the spec it was felt independence was compromised anyway ("common culture" perhaps...).
All of which is not relevant to the FADEC software which is a different beast and may well have used a different (but still safety-critical) development methodology.
With regards to this incident, based on the information published so far all the software appears to have functioned correctly, which means we are looking at a different cause (although I take the point that there could have been something going on between sampling intervals or a sensor failure).