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  #11  
Old 02-20-2020, 01:45 PM
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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 : 02-20-2020 at 01:52 PM.
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  #12  
Old 02-20-2020, 01:48 PM
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Originally Posted by Thermos View Post
The FAAís 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, itís up to the SACAA to determine how it applies to you but most CAAs have reciprocal agreements to recognize other countriesí ADs. So best case, I wouldnít expect to see anything definite before late March.

Like you, Iím 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 theyíll be as responsive in this case.

Dave
Thanks for the feedback Dave. Exactly what I wanted to know. Letís hope for the best!
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  #13  
Old 02-20-2020, 08:12 PM
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Yes, its in the AD.

...Ēgaseous 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. Ē
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 02-20-2020, 09:54 PM
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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 : 02-21-2020 at 08:37 AM.
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  #15  
Old 02-22-2020, 11:59 PM
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Quote:
Originally Posted by rv6ejguy View Post
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.
This sounds quite accurate compared to what I was taught in engineering school.

Does anyone here know at what engine hours these crankshaft failures occurred? Is there a trend or was it random high/low hours? Itís not going to make me fly if all failures were at high engine times, but Iím curious and might as well make up some time while waiting for answers from FAA/Superior...(sigh)
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  #16  
Old 02-26-2020, 04:56 AM
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Article on Avweb from yesterday. Superior's response. Not really new news though.

https://www.avweb.com/aviation-news/...rankshaft-nprm
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  #17  
Old 02-26-2020, 06:32 AM
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Originally Posted by JPGrobler View Post
Does anyone here know at what engine hours these crankshaft failures occurred? Is there a trend or was it random high/low hours?
IIRC from the conversation with my engine builder, the crankshaft he replaced (one of the three failures that triggered the AD) had a little under 700 hours on it.

Dave
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Last edited by Thermos : 02-26-2020 at 06:39 AM.
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  #18  
Old 02-28-2020, 07:31 AM
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Unlimited is communicating with Superior this afternoon and I’ll pass on what I find out.
I just got off the phone with my engine builder, who had just finished a conversation with Bill Ross from Superior.

Bill Ross and Superior claim that the crankshafts that failed had all been tested by an "independent" (Superior's words) organization who verified that each crankshaft met its ASTM materials standards. Nothing new here, they've already said as much in a press release.

They also claimed in this morning's call that these crankshaft failures were the result of abuse - one due to an engine overspeed, another due to a previous prop strike, and the third due to the throttle being advanced to full power on an engine that hadn't warmed sufficiently. I don't know the conditions surrounding the first two failures, but the third is sending up some BS flags for me as I live in New England - if firewalling the throttle on a cold engine is enough to fail the crankshaft, then we'd have engine failures galore around here every Winter.

Unfortunately, this AD could drag on for awhile after the comment period closes if the FAA and Superior can't come to an agreement on root cause and methods of compliance.

Dave
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Last edited by Thermos : 03-01-2020 at 05:55 PM.
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  #19  
Old 02-28-2020, 09:52 AM
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Previous prop strike-valid cause, overspeed- valid cause, Revving up when cold- I hope the design is not that marginal...
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  #20  
Old 03-01-2020, 11:23 AM
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Previous prop strike-valid cause, overspeed- valid cause, Revving up when cold- I hope the design is not that marginal...
I wholeheartedly agree with you. Sounds like their grasping at straws here...

I hope the wait doesnít have to continue much longer after 16 March. And I do hope the best decision is made to get everyone safely back in the air again. I donít want to fly behind an engine I donít trust...been there, done that, got the T-shirt!
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