Re: Boeing 777 - Totally Irresponsible?

Date:         04 Jan 97 03:55:52 
From:         Bill Chivers <Bill@chivcons.demon.co.uk>
Organization: Chivers Consultants
References:   1 2
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In article <airliners.1996.3056@ohare.Chicago.COM>, MegaZone
<megazone@livingston.com> writes
>
>See, it's called redundancy.  Most of the time there are at least 3, usually
>4 or more, systems for each task.  And on critical cases different software
>is run on the different systems.  So that you can *never* have a single
>point of failure in the code cause a crititcal failure.  You would have to
>have *all* systems fail in the same way at the same time, despite the
>different code.  The odds of that are incomprehensible.

>Take the Space Shuttle.  It has 5 main computers.  To my knowledge there
>has never been a simultaneous failure that threatened a mission due to
>software.
>
>No one is stupid enough to fly an airfraft with FBW without redundant systems
>and with the possibility of universal code failure.
>

Hmmm. I'm sure someone will correct me if I'm wrong, but I'm sure I have
a recollection of reading (in 'Flight') that the 777 has 3 sets of
identical FBW software, and I think that this is the point which is of
concern, i.e. that if a combination of inputs which causes a 'crash'
(software I mean) occurs, all the systems will go down together.

Whereas Airbus employ code written by different teams, and it could
therefore be argued that the chances of total failure are less, because
a combination of inputs which will simultaneously crash *different* sets
of software should be vanishingly unlikely.

The counter argument is that different software teams still come from
the same industry, with the same way of thinking, working from the same
specification, and are therefore likely to make similar mistakes.

As for myself, I don't know, not being a software expert. And as I don't
know enough to make an informed judgement, it concerns me. Still, I
don't suppose I'll fly in a 777 for a few years - no prospect of a job
on one and I don't earn enough to jet around the world!

One things for certain - come New Years Eve 1999, I'm not planning on
being on, in or near anything computer controlled. I'll be hiding deep
underground with my savings (in cash) stuffed underneath my mattress ;-)

Bill Chivers
'my other signature file has something funny at the bottom of it'