Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Tue, 08 Jun 2004 09:42:56 -0400
Message-ID: <redirect-144117@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: Re:  Safety
MIME-Version: 1.0
Content-Type: text/plain;
	charset="Windows-1252"
Content-Transfer-Encoding: 7bit
Importance: Normal

<<That rudder cable is not going to break no matter how hard you apply the
brakes.
By the way, obviously non-structural, non-aerodynamic changes are fine.  If
you aren't sure you know the difference vs. changes that affect aerodynamics
or the structure's performance (or any other aspect of function like fuel
delivery), just stick to the plans.

Ed de Chazal>>

I certainly agree with most of Ed's points.  However, statements like "is
not going to break" are hard to accept.  Anything can fail.  Just because a
design has been around a while and generally successful doesn't mean it is
perfect and can't be improved.  And just because it isn't perfect doesn't
mean it is "faulty."  It does behoove us to consider any failure mode and
the ramifications of that failure mode.  If the failure mode induces other
failures then the severity of that failure mode is higher than if it
doesn't.  The rudder control/brake system/nose wheel steering is an example.
Our planes, of course, don't have nose wheel steering and we have accepted
that, although the lack of it creates potential problems, notably the
severity of a brake failure.  The plane can probably be landed without
rudder control, as the brakes will steer it on the ground.  It can also be
successfully landed without one brake, at least to limit the result to an
low-speed crash.  However, if the rudder control failure makes the brakes
unusable and there is no nose wheel steering to back it up, then a single
failure could lead to an unpleasant outcome and the idea that the brake
system is a backup for the rudder control is faulty.  However, I agree that
adding complexity to solve one problem can create others.  The goal is to
solve single-point failure modes WITHOUT adding more systems.  I'm not
convinced that "just sticking to the plans" will automatically result in an
aircraft that is the best that can be made.  The real trick, as Ed implied,
is to know when to change and when not to change.

Gary Casey