From: AFE12@aol.com
Message-ID: <74.6917942.27865a12@aol.com>
Date: Thu, 4 Jan 2001 17:58:26 EST
Subject: Re: FADEC redundancy?
To: ericparlow@hotmail.com, lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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<< Questions???
 ERic-- >>

The wealth of information provided was impressive.  I understand how each 
cylinder has its own control circuitry and how a failure of one cylinder's 
control circuitry is taken up by the controller of the opposing cylinder.  
These paired cylinder controllers are called ECU's and it takes three of them 
to run the 550.  Each of the three appears to be tied to just two cylinders.  
I have just one yes-or-no question:

On the IOF-550 (not the four cylinder), if we lose or unplug one whole ECU do 
all six cylinders keep running?

It appears that if the two cylinder controls in each ECU are electrically 
separate and fed from separate voltage sources, then the "6 computer / 3 ECU" 
system does have individual computer redundancy, but not redundancy in the 
event of one ECU box or it's cable going down as a unit.  It also seems that 
the engine cannot run on one computer, but takes at least three evenly 
distributed between the cylinders (two for the 240).  Obviously, the terms 
"ECU" and "computer" are not synonymous in this case and this is confusing.  
The reliability calculation becomes more complicated, but is still less than 
it would be if one computer could run all 6 cylinders.  Again, this is not 
everyone's definition of redundancy.  I'm asking what that is, and that 
admittedly diverse answer can only come from the customer base.  TCM, 
Lycoming, and all other engine control vendors could consider the answers on 
this list to be an uncontrolled market survey.  I know I'm curious.

Eric Ahlstrom
Star Aerospace LLC
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