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Propellor falls off Rex Saab 340 in NSW Australia

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Propellor falls off Rex Saab 340 in NSW Australia

Old 21st Mar 2017, 17:17
  #21 (permalink)  
 
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In my perusal of the data, that is extremely rare in powerplant related failures.

Such things as gun-drill tool marks, unchamfered oil holes, and quench cracks come to mind.

Barret1 probably has some more in mind
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Old 21st Mar 2017, 17:21
  #22 (permalink)  
 
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Parallel thread

http://www.pprune.org/australia-new-...highlight=saab

And yes, I've seen a raw material defect or two - foreign material inclusions, a forging lap so blatant it failed on the first engine runup, sharp-corner stress riser, crack originating from the p/n marking area. . .

Highly engineered materials that must be properly manufactured, or they are guaranteed to fail!

Last edited by barit1; 21st Mar 2017 at 17:38.
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Old 22nd Mar 2017, 07:49
  #23 (permalink)  
 
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That leads to the prop-torque inducing a prop separation.
The discolored section of the shaft does not indicate a sudden, prop-toque induced event...
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Old 22nd Mar 2017, 21:08
  #24 (permalink)  
 
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Prop/fan shafts can fail for a variety of reasons. I recall a fan shaft failure on a nearly new turbofan engine a few years back that was traced to the wrong anti-seize assembly lube being used.
I don't recall the details (and metallurgy isn't exactly my area of expertise), but IIRC the assembly lube promoted stress corrosion on the threads that lead to the shaft failure.
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Old 23rd Mar 2017, 03:07
  #25 (permalink)  
 
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A previous 340 event where the prop was lost, in an identical manner to this, was found to be caused by a slag inclusion in the shaft. DC-10 had a similar event where a fan disc contained inclusions and let go with eye watering results.
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Old 23rd Mar 2017, 11:53
  #26 (permalink)  
 
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A very big difference in (slag-inclusion) detectability between a thin wall shaft and a very thick fan disk both during manufacture and in-service shop visits.
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Old 13th Apr 2017, 04:35
  #27 (permalink)  
 
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Prelim Report

Well here's the prelim report, seems the PPRuNe aib got it more or less right; Investigation: AO-2017-032 - In-flight propeller malfunction involving SAAB 340 VH-NRX, 19 km SW of Sydney Airport, NSW, on 17 March 2017
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Old 14th Apr 2017, 07:23
  #28 (permalink)  
 
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Originally Posted by spinex View Post
Indeed

Of note
This is the first known critical failure of this type
Really curious if they will be able to pinpoint the root cause.
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Old 14th Apr 2017, 14:13
  #29 (permalink)  
 
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Straight forward metallurgical techniques/examinations. including possible abusive machining. Typically this kind of stuff is batch related and a get well plan already in progress.

No doubt the ATSB or equiv is involved in the precise details of the cause and they will probably close out their invest when satisfied that the regulator has addressed the findings.
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Old 14th Apr 2017, 18:17
  #30 (permalink)  
 
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Classic helical torsional stress fracture. Will be interesting to see what the underlying cause was.
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Old 14th Apr 2017, 18:25
  #31 (permalink)  
 
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Sounds like corrosion may be a factor.
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