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  #11  
Old Yesterday, 02:45 PM
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Thermos Thermos is offline
 
Join Date: Jan 2005
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Originally Posted by JPGrobler View Post
Anyone have an idea of the timeline looks like for an AD like this? What to expect in the near future and how to get into the air again ASAP? This is the first time I’ve been affected by an AD and have no idea what I’m in for...
The FAA’s comment period for this AD closes on 16 March. At that point they will look at inputs from Superior, AOPA and other interested parties and decide to either keep the AD as-is (likely), amend it (possible) or withdraw it (unlikely). If the AD is put into US law, it’s up to the SACAA to determine how it applies to you but most CAAs have reciprocal agreements to recognize other countries’ ADs. So best case, I wouldn’t expect to see anything definite before late March.

Like you, I’m affected (and only a few weeks from being finished and ready to fly ). The shop that built my engine, Unlimited Aero Engines, repaired one of the failed engines that led to the AD and Superior was very good about sending replacement parts at no charge and paying for labor. I hope they’ll be as responsive in this case.

Unlimited is communicating with Superior this afternoon and I’ll pass on what I find out.

Dave
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Last edited by Thermos : Yesterday at 02:52 PM.
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  #12  
Old Yesterday, 02:48 PM
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JPGrobler JPGrobler is offline
 
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Originally Posted by Thermos View Post
The FAA’s comment period for this AD closes on 16 March. At that point they will look at inputs from Superior, AOPA and other interested parties and decide to either cancel, amend or keep the AD as-is. If the AD is put into US law, it’s up to the SACAA to determine how it applies to you but most CAAs have reciprocal agreements to recognize other countries’ ADs. So best case, I wouldn’t expect to see anything definite before late March.

Like you, I’m affected (and only a few weeks from being finished and ready to fly ). The shop that built my engine, Unlimited Aero Engines, repaired one of the failed engines that led to the AD and Superior was very good about sending replacement parts at no charge and paying for labor. I hope they’ll be as responsive in this case.

Dave
Thanks for the feedback Dave. Exactly what I wanted to know. Let’s hope for the best!
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  #13  
Old Yesterday, 09:12 PM
sblack sblack is offline
 
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Originally Posted by Tandem46 View Post
Yes, its in the AD.

...”gaseous nitrocarburization resulted in excessive residual white layer forming on the assemblies. This white layer is brittle and can lead to spalling or fatigue cracking of the crankshaft assembly as a result of the normal mechanical loads during engine operation. ”
Does anyone know if this gaseous nitro carburization occurred during mfg, like during nitriding etc, or is it something that occurs during operation? I have never heard this term before.
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  #14  
Old Yesterday, 10:54 PM
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rv6ejguy rv6ejguy is offline
 
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Does anyone know if this gaseous nitro carburization occurred during mfg, like during nitriding etc, or is it something that occurs during operation? I have never heard this term before.
White layer formation can only happen during the manufacturing process. Nitro carburization is an intentional, surface steel hardening process used similarly to gas nitriding but at lower temperatures to minimize part distortion.

My understanding is that quench oil vapor contamination during part heating is thought to be a likely cause of white layer formation but someone with more real-world knowledge of heat treating, hardening and quenching processes could say more on the subject.

White layer formation is often hard to detect, say optically, without an actual hardness (ball) test. I know some machinists have run into the problem where high temps induced by the machining process can cause a white layer to form which kills the tool pretty fast.

It would appear to be a process control defect or oversight here to cause this issue as is usually the case where some cranks fail while the majority of them live for thousands of hours. We have seen process control issues at Lycoming also before as well as alloy recipe changes, resulting in crank failures. Nobody is immune. This stuff is all really critical to get consistently reliable cranks. A tiny change in the established and validated processes or material can cause premature failure.

I learned a bit about hardening and quenching steel decades ago from a old and wise gunsmith friend. My memory maybe isn't correct on some details here so someone with intimate knowledge of this subject, please correct any errors.
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Last edited by rv6ejguy : Today at 09:37 AM.
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