Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Wed, 09 Jun 2004 19:32:42 -0400
Message-ID: <redirect-146477@logan.com>
From: Hamid Wasti <hwasti@starband.net>
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Subject: Re: [LML] Rutan tries for 100-km. suborbital flight with SpaceShipOne
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Rob Logan wrote:

>     THE INSTRUMENT DISPLAY FAILED on that flight about one-third of
> the way into the burn, but Melvill continued the trajectory by
> referencing the horizon through the windows and was able to reach the
> target apogee.  The problem is believed to be the potentiometer that
> adjusts display brightness - the calculations proceeded correctly but
> the acceleration pulled the wiper off the contact.  Once the motor
> stopped, the display came back on.  The pot has since been hard-wired. 


This why some of us scream when we hear someone post things like "It is 
just a pot.  It works great in my car, so I am going to put it in my 
plane.  It has proven itself in automotive use so it is a proven 
design."  Aaaaarrrrrgggghhhhhh!

This ties in well with the safety discussion.  Sure, you can make 
changes to the design (you are the manufacturer) but can you be sure 
that a "minor" change will not have major consequences in ways that you 
did not anticipate?  A stupid little pot for something as unnecessary as 
controlling the backlight intensity in a display that is used in the 
daytime only, brings down the backlight, which brings down the display 
which could have aborted the test or even brought down the aircraft. How 
many people could have thought through the exact sequence of events when 
they were installing that pot?  Apparently none.  And the caliber of 
people on that project is most probably a bit higher than the caliber on 
this list.

Remember the axiom:  For the loss of the nail, the horseshoe was lost. 
For the loss of the shoe the horse was lost.  For the loss of the horse 
the rider was lost.  For the loss of the rider the battle was lost.  For 
the loss of the battle, the war was lost.  For the loss of the war, the 
kingdom was lost.  Yes, I do mean to tell you that the whole kingdom was 
lost because someone said "It is just a stupid little nail....."

Hamid