Re: AIRBUS vs. BOEING (cont...)

From: (ExpAero)
Organization: America Online, Inc. (1-800-827-6364)
Date:         22 Jun 95 03:07:36 
References:   1
View raw article
  or MIME structure

>>Use of a single design of computer and software to drive the FBW - the
>>possibilities of common mode failures must be obvious.

The theoretical possiblity of common mode failures in complex systems may
seem obvious but determining the probabity of simultanious occurrence of
such failures it not.   I assume you would prefer not to have two pilots
on the same flight who are identical twins since they may have a "common
mode failure" at the same time?  Granted at this stage humans are a more
complex system that a simple 777 flight control system but the issue is
really the same.  Further, in order to get redundant, asychronous,
processors to operate together properly, the software requirements must be
so detailed as to result in almost the same software (and errors) even if
multiversions are developed.  This issue could provide fodder for a whole
string on it's own.  I've not seen any literature that purports to prove
that redundant system designs with multiversion software actually result
in a lower probability of simultanious common mode errors of any kind.
Some academic investigations into the subject have actually indicated

>>As I understand it,no protection against low energy (windshear)

I'm confused by this statement.  Are you referring to some autothrottle
feature that would automatically advance the throttles based on some
signal from the windshear warning system?  The 777 does have a windshear
warning system with associated flight director cues.  This is required for
all commercial aircraft of its type operated in the U.S.  Is there
something more that you believe the 777 lacks?