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NTSB letter and flutter.

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psm(at)att.net
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Posted: Thu Oct 29, 2009 8:42 am Post subject: NTSB letter and flutter.

After the last round of heated discussion over the NTSB letter regarding flutter I decided to check the language in the actual letter.  The first paragraph of the letter in question is copied below.



 The letter itself says:  "It appears . . .flutter . . . likely source".  This is a country mile away from a statement that flutter caused the accidents.  It is merely a conjecture that is presented for further consideration and testing.



 Paul

 XL awaiting engineering changes



 --------------------------------------------------------------------------------------

  The National Transportation Safety Board has investigated a series of in-flight structural breakups of Zodiac CH-601XL airplanes designed by Zenair, Inc., that occurred in the United States in the last 3 years. The Safety Board is also aware of several in-flight structural breakups of CH-601XLs that have occurred abroad. It appears that aerodynamic flutter is the likely source of four of the U.S. accidents and of at least two foreign accidents. The Safety Board believes urgent action is needed by the Federal Aviation Administration (FAA) to prevent additional in-flight breakups. 

 ---------------------------------------------------------------------  

    [quote][b]

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Fri Oct 30, 2009 5:31 am Post subject: Re: NTSB letter and flutter.

 	  psm(at)att.net wrote: 	
		  



 The letter itself says:  "It appears . . .flutter . . . likely source".  This is a country mile away from a statement that flutter caused the accidents.  It is merely a conjecture that is presented for further consideration and testing.



 Paul

 XL awaiting engineering changes



 - 	




Well the same letter also said this, "There is substantial circumstantial evidence that flutter occurred in some, if not all, of the above-cited accidents." Which about a city inch from saying flutter was the cause.

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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

psm(at)att.net
Guest

Posted: Fri Oct 30, 2009 6:24 am Post subject: NTSB letter and flutter.

It is an unfortunate truth that there are many different ways to 

interpret complex statements in our language.  For people whose 

reading is primarily entertainment/literature or newspaper articles 

it is useful to ignore many of the words in each sentence to get the 

core meaning.  In technical writings this will lead you down the wrong path.

If you ignore the qualification that the "Evidence" is substantial 

and circumstantial in "substantial circumstantial evidence" and you 

already hold the belief that flutter is behind the accidents then 

that statement can be comforting.  However, if the writer really 

believed there was enough evidence to establish the fact he would not 

have used the qualifications of "Substantial" and "Circumstantial" in 

his statement.  This removes his assertion two different times from a 

direct statement..  He is really saying (in technical jargon) flutter 

is a candidate for the cause of the accidents.  However there is no 

actual evidence but there is circumstantial suggestion that supports 

this notion.  In addition, the circumstantial evidence isn't really 

consistent but only somewhat supporting the notion which means it is 

substantial rather than convincing.  He further reduces the 

confidence by referring to "Some" of the accidents instead of "All" of them.

Just like the opening paragraph of the letter, the writer uses two 

qualifying phrases to limit his confidence in the statement that 

flutter is behind the accidents.  Once again the statement is an 

argument for further study rather than a definitive assertion.

I have heard comments that the ZBAG group reached the conclusion that 

flutter was the cause of all the problems with Zodiac XLs and somehow 

got the NTSB to consider this conclusion.  For them, the NTSB letter 

can provide support for their conclusion.  For someone who carefully 

reads the NTSB letter without already being convinced of the flutter 

argument the letter says just the opposite thing.  It allows for the 

possibility that flutter is the cause but carefully refrains from 

actually supporting that conclusion.

What the NTSB letter is crystal clear about - with no qualifying 

language at all - is that there have been a lot of fatal accidents 

and the fleet should be grounded.

Paul

XL awaiting engineering changes

At 06:31 AM 10/30/2009, you wrote:

 	  Quote: 	
		  psm(at)att.net wrote:

 >  The letter itself says:  "It appears . . .flutter . . . likely 

 source".  This is a country mile away from a statement that flutter 

 caused the accidents.  It is merely a conjecture that is presented 

 for further consideration and testing.

 >

 >  Paul

 >  XL awaiting engineering changes

 >

 >  -

Well the same letter also said this, "There is substantial 

circumstantial evidence that flutter occurred in some, if not all, 

of the above-cited accidents." Which about a city inch from saying 

flutter was the cause.

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