From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Avionics:  Black Art or Science
To: lml
Date: Wed, 19 Apr 2006 22:56:02 -0400
Message-ID: <web-1073998@logan.com>
In-Reply-To: <17E9FE5945A57A41B4D8C07737DB60720372569C@PDX-MX6.stoel.com>
References: <17E9FE5945A57A41B4D8C07737DB60720372569C@PDX-MX6.stoel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 8bit

Posted for "Halle, John" <JJHALLE@stoel.com>:

  Brent writes (below) that electrons follow rules that can (sooner or later)
be understood through the use of reason.  Reminds me of the story about the
lawyer who wrote a one-page legal document and sent a bill for $500 with a
single item: "draft document: $500."  The client objected that it could not
have taken more than a half hour to write the document.  The lawyer sent back
a revised bill with two items: 1. "draft document: $50"; 2. "knowing what to
write: $450."
  
  Having just finished replacing my panel, I must, at least superficially 
agree
with Brent.  The problem is that, as anyone who has ever looked at the back of
a modern instrument panel knows, there are electrons going through hundreds of
wires.  Some of them are carrying digital data (whether the electrons are
analog or not) that may be AIRINC, RS232 or something else, some are carrying
a simple current that is used to power something; some are carrying a current
that is used to transmit data. A huge number of them are going to something
called "ground", a simple concept until you try to actually do it right.  They
go to and from various boxes that have unbelievebly complex circuits etched
onto chips and other devices.  These boxes either do or don't talk to each
other using protocols understood only by software engineers.  In theory we
don't have to understand how all this works because all we have to do is
follow the installation and setup directions, 100% of which are wrong or
incomplete in some respect and many of which are almost totally wrong or
incomplete.  If something is not working properly, there are usually at least
ten possible explanations that occur even to a non-engineer, to say nothing of
the fifty explanations that occur to engineers.  Each one of these
explanations involves the assumption that electrons follow simple rules that
can be understood through the use of reason.  The black art is knowing which
explanation to investigate first.