Re: 777 engine imbalance (Business Week, 1/29)

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         08 Feb 96 03:21:08 
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>The January 29th issue of Business Week has a pretty long article
>on how the FAA certified the 777 without properly looking into
>the issue of individual blade failures in the new engines.

Interesting article, though I couldn't decide if I thought it had some
merit or if it was mostly journalistic sensationalism.  I'd love to see
some more informed opinions on the article.

>Are thse allegations as serious as the magazine make them out to be?
>It talks about a 1993 incident where a Cathay Pacific 747 almost made
>a water ditching after such a blade separation...

I read this and scoffed, as I did when they talked about instruments
on the 777 being unreadable due to engine vibrations.  Sounds pretty
absurd, right?  Just shut the engine down!

Then, nearly at the end of the article, they mentioned windmilling
engines and it dawned on me that just shutting the engine down isn't
good enough, since it will still windmill and thus still produce a
pretty decent vibration if it's massively out of balance.

It still seems like they ought to be able to simulate the situation
reasonable well, since they have vibration data from test-stand runs
of the engines with intentionally failed blades.  This information
could be used to appropriately shake an airframe on the group, or so
it would seem.  Perhaps someone can enlighten me on this point in the
same way that the windmilling comment finally opened my eyes.

--
Karl Swartz	|Home	kls@chicago.com
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