Re: Boeing and Dreamliner

[Marin David Condic <nobody@noplace.com>]

Precisely. The designers had looked at the range of possible inputs and 
concluded that if an input were to get beyond some point, this would 
indicate a sensor failure because the flight envelope could never 
contain that as valid data. That is the Failure Detection part. They 
further designed the unit to shut down the channel that had the presumed 
bad sensor. That was the accommodation part. It worked *exactly* as it 
was designed to work doing *precisely* what it was supposed to do. The 
software didn't fail. It didn't have a bug. It worked 100% according to 
plan. The problem was that in a different set of circumstances, this was 
not the desired behavior and nobody bothered to check.

Its a little like these lawsuits against gun manufacturers when 
criminals use their products to kill someone. The argument from the gun 
manufacturer ought to be "Look, you pointed the thing at someone, 
squeezed the trigger and that person died. It worked exactly as designed 
and there was no manufacturing flaw. What's your problem???" :-)

MDC



Mike Silva wrote:
> 
> 
> The difference is that the Ariane 4 software behaved *exactly* as
> designed and intended for *all* ranges of inputs, for the Ariane 4. 
> Raising an exception was not "failing catasrophically" but was the
> correct behavior, triggering the correct shutdown of the unit, for the
> data in question.  What data limitation is there to document, when the
> software performs correctly for all data?
> 
> Then the Ariane 5 people came along, and they had an unstated, and
> apparently even unrecognized, requirement for *different* behavior
> over a certain range of data.  That certainly does not mean there was
> a bug in the Ariane 4 software.
> 
> Mike


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Marin David Condic
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