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From: MRE <Marc.Enzmann@web.de>
Newsgroups: comp.lang.ada
Subject: Re: OT?: AF 447 and avionics software
Date: Sun, 7 Jun 2009 01:33:50 -0700 (PDT)
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Date: 2009-06-07T01:33:50-07:00
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On 6 Jun., 12:38, sjw <simon.j.wri...@mac.com> wrote:
> On Jun 5, 8:22=A0am, MRE <Marc.Enzm...@web.de> wrote:
>
> > The rocket scientist that came to this brilliant conclusion seems to
> > be a real expert in the field of complexity theory.
> > Thing is: even if you use analog electronics 50's style you can not be
> > sure that you have checked all possible combinations of events.
>
> I think the difference is that analog systems tend to break in much
> less complex ways than digital ones. A run-time exception is likely to
> result in catastrophic and unpredictable misbehaviours. Who would have
> thought that buffer overflows could lead to botnets overloading the
> net with spam?

The issue in flight-systems is: we are using digital systems to
control
analog behaviour. Therefore the level of complexity (is hopefully)
not
determined by the solution but by the problem.

Why would you think that a faulty OpAmp in a complex control circuit
has
less than unpredictable behaviour than a crash in a software system?

The problem is definitely NOT digital flight controls, whatever the
self-proclaimed pundits state. It has been universally acknowledged
wisdom in
the aerospace industry, that accidents / incidents rarely occur due to
one
single failure but due to a combination of problems. If you look at
the
statement quoted here http://www.time.com/time/world/article/0,8599,1902421=
,00.html
this is however stated to be true only for digital systems. And
that's
rubbish.

Regards,

Marc