Lycoming Connecting Rod Bushing AD 2024-21-02

[ArtVandelay]

I found in the paperwork the part number AEL-11750-S.  That is different than the Lycoming part number LW-11750.  For all you smarter than me folks…would my part with that part number still fall under the AD?

I have parts with SL, AEL, LW, and no prefix at all, I assume AEL and SL are different manufacturers (superior, continental, etc).

[EricJ]

2 hours ago, Greg Ellis said:

I found in the paperwork the part number AEL-11750-S.  That is different than the Lycoming part number LW-11750.  For all you smarter than me folks…would my part with that part number still fall under the AD?

If it was me, I'd contact Hyfast and see if those rods contained the affected bushing.

[DCarlton]

Update.  I'm no expert; just trying to connect the dots.  It looks like AD 2024-21-02 is an expansion of AD 2017-16-11 which points to LYC SB 632B for action.  SB 632B provides Table 1 with serial number of affected engines.  For overhauled engines, Table 2 provides shipment dates for suspect bushings.  IAW para 1.B, I've consulted with my overhaul shop to determine if I may have suspect bushings.  

Again.   I'm not a mechanic or an expert.  Just an owner trying to get ahead of a potentially painful problem.  My engine has less than 200 hours.  

[AndreiC]

@N201MKTurbo: just out of idle curiosity, assuming one would want to do the bushing replacement (which I hope never to have to do, just to monitor). How many hours would you estimate it takes for an experienced engine shop to take the cylinders off, remove the connecting rods, replace the bushings, and reinstall everything? Is it something that, say, Poplar Grove could do in one full day of work (so one could fly in and out the same day), or is this a several day project? I assume the parts would add up to about $1200 (rod bolts and nuts, and all the gaskets that would have to be replaced), I am trying to estimate labor cost.

[PT20J]

From the FAA Docket FAA-2024-1695 https://www.regulations.gov/document/FAA-2024-1695-0001

Background

The FAA received five reports of uncontained engine failures and IFSDs due to failed connecting rods on various models of Lycoming reciprocating engines that were overhauled or repaired using any replacement part listed in Table 2 of Lycoming Mandatory Service Bulletin (MSB) No. 632B, dated August 4, 2017 (MSB 632B), which was shipped from Lycoming during the dates listed in Table 2 of MSB 632B. As a result, the FAA issued AD 2017-16-11, Amendment 39-18988 (82 FR 37296, August 10, 2017) (AD 2017-16-11), which required an inspection of connecting rods and replacement of affected connecting rod small end bushings.

Since the FAA issued AD 2017-16-11, a manufacturer investigation determined that affected connecting rod small end bushings may be installed on additional populations of Lycoming engines. The manufacturer also determined that degradation of the connecting rod small end bushings is detectable during oil change inspections. This condition, if not corrected, could result in connecting rod failure with consequent uncontained engine failure, total engine power loss, IFSD, and possible loss of the airplane.

https://www.lycoming.com/sites/default/files/attachments/SB632B%20Connecting%20Rod%20Identification.pdf

[MikeOH]

I can't help but think there will be far more maintenance induced engine failures after many have their engines torn apart to check the bushings!

IIRC, Mike Busch is not too wild about inadvertent pulling of a cylinder...let alone ALL four at the same time!  I didn't think it was a good idea to rotate the crankshaft after pulling a cylinder; how are you going to pull ALL four AND the rods without moving the crank?

But I'm not an A&P, so WTHDIK?

[PT20J]

1 minute ago, MikeOH said:

I can't help but think there will be far more maintenance induced engine failures after many have their engines torn apart to check the bushings!

IIRC, Mike Busch is not too wild about inadvertent pulling of a cylinder...let alone ALL four at the same time!  I didn't think it was a good idea to rotate the crankshaft after pulling a cylinder; how are you going to pull ALL four AND the rods without moving the crank?

But I'm not an A&P, so WTHDIK?

The AD does not require any tearing apart of engines. It simply requires inspection of the filter element and suction screen at routine oil changes. The only time you need to remove cylinders is if you find bronze chips.

[DCarlton]

38 minutes ago, PT20J said:

The AD does not require any tearing apart of engines. It simply requires inspection of the filter element and suction screen at routine oil changes. The only time you need to remove cylinders is if you find bronze chips.

That’s not the way I read the 2017 AD.  Although I would prefer your interpretation.  

[MikeOH]

Just now, DCarlton said:

That’s not the way I read the 2017 AD.  Although I would prefer your interpretation.  

I did note that the inspection required by the 2017 AD (if you and I are correct) does NOT require the removal of the connecting rod.  It requires a special tool that puts a known pressure on the bushing; if the bushing moves out of the connecting rod then it is defective and must be replaced (which then requires removal of the rod). 

[PT20J]

3 minutes ago, DCarlton said:

That’s not the way I read the 2017 AD.  Although I would prefer your interpretation.  

I was referring to the new AD. The 2017 AD should have been complied with by now.

[N201MKTurbo]

4 hours ago, AndreiC said:

@N201MKTurbo: just out of idle curiosity, assuming one would want to do the bushing replacement (which I hope never to have to do, just to monitor). How many hours would you estimate it takes for an experienced engine shop to take the cylinders off, remove the connecting rods, replace the bushings, and reinstall everything? Is it something that, say, Poplar Grove could do in one full day of work (so one could fly in and out the same day), or is this a several day project? I assume the parts would add up to about $1200 (rod bolts and nuts, and all the gaskets that would have to be replaced), I am trying to estimate labor cost.

It will take about 8 hours to R&R all the cylinders. For most shops, they will need to send the rods out to have the bushings changed. This will, take about two weeks. 
 

I would plan on having your plane down for 3 - 4 weeks at a minimum.

[jetdriven]

9 hours ago, N201MKTurbo said:

It would be the one in the rod. The ones that are on the ends of the pin are aluminum.

 

But the newest ones now are some kind of phosphor bronze again. I don’t know if they’re the same alloy as the small end rod bushing but they’re not aluminum.

[jetdriven]

3 minutes ago, N201MKTurbo said:

It will take about 8 hours to R&R all the cylinders. For most shops, they will need to send the rods out to have the bushings changed. This will, take about two weeks. 
 

I would plan on having your plane down for 3 - 4 weeks at a minimum.

Maybe if it’s on an engine stand, you can R&R all cylinders in  8 hours but on the plane by the time we take the baffling and everything else apart it’s quite a bit more than that. And then you still have to end up honing the cylinders and putting new rings on it and you gotta file fit the rings to the right end gap and then you still got to check the dry tappet clearance too. Then reassemble the whole airplane with the exhaust, the induction tubes, the baffling, spark, plug leads, plugs, valve train,  and everything else.

[N201MKTurbo]

1 minute ago, jetdriven said:

Maybe if it’s on an engine stand, you can R&R all cylinders in  8 hours but on the plane by the time we take the baffling and everything else apart it’s quite a bit more than that. And then you still have to end up honing the cylinders and putting new rings on it and you gotta file fit the rings to the right end gap and then you still got to check the dry tappet clearance too. Then reassemble the whole airplane with the exhaust, the induction tubes, the baffling, spark, plug leads, plugs, valve train,  and everything else.

If I was just pulling the cylinders to inspect the bushings, I wouldn’t do most of that unless there were other problems. No need to hone and re-ring or check the valve lash, unless something changed. I wouldn’t even change the rod bearings unless they re-machined the rod. What’s the point? They were all working fine before. R&R ing the cylinder won’t change any of that stuff.

If the owner wanted all of that stuff changed, I would, but I wouldn’t require it.

[DCarlton]

27 minutes ago, PT20J said:

I was referring to the new AD. The 2017 AD should have been complied with by now.

Yep.  Everyone with an engine overhauled in late 2015 to late 2016ish needs to take a close look at their paper trail.  However not clear now why compliance requirements are different on the two ADs.  

[PT20J]

18 minutes ago, DCarlton said:

However not clear now why compliance requirements are different on the two ADs.  

It was explained in the excerpt from the Docket I posted earlier.

3 hours ago, PT20J said:

The manufacturer also determined that degradation of the connecting rod small end bushings is detectable during oil change inspections.

 

[MikeOH]

Do we know what the underlying defect actually is?

Speculation based solely on the inspection in the SI which requires a special tool to try and push out the bushing, I'm guessing the bushing OD was out of spec on the low side (insufficient interference fit).

[MB65E]

Back in on the 2017 rod AD, 
I was asked to do a few of the inspections. I researched it a bit. At the time to my knowledge there was a tooling kit to replace the bushings with the rods on the crank. I ended up not doing the inspections/replacements.  I’m also sure the work can be done with out splitting the case. I think this AD is going after some of the those same failure modes. 
I found my Aircraft engine specialties invoice from 2012. It has the affected rod end bushings listed on the invoice. What’s also entertaining is that LW-10646 rod assembly also has another PN associated with it. LW13756 is the Rod casting number. Maybe it was an installation issue at Lycoming. The Service instructions speak of burnishing the bushing once installed. Maybe those from lycoming missed that process. 
But really, all we need to is watch for the chips of bronze in the oil at this time. 

-Matt
 

[DCarlton]

10 hours ago, MB65E said:

Back in on the 2017 rod AD, 
I was asked to do a few of the inspections. I researched it a bit. At the time to my knowledge there was a tooling kit to replace the bushings with the rods on the crank. I ended up not doing the inspections/replacements.  I’m also sure the work can be done with out splitting the case. I think this AD is going after some of the those same failure modes. 
I found my Aircraft engine specialties invoice from 2012. It has the affected rod end bushings listed on the invoice. What’s also entertaining is that LW-10646 rod assembly also has another PN associated with it. LW13756 is the Rod casting number. Maybe it was an installation issue at Lycoming. The Service instructions speak of burnishing the bushing once installed. Maybe those from lycoming missed that process. 
But really, all we need to is watch for the chips of bronze in the oil at this time. 

-Matt
 

I'm planning to reread the two ADs again today along with the SBs, but I'm stumped from a process standpoint as to how to rectify the compliance requirement differences between the 2024 and 2017 ADs.  I believe the 2017 AD requires bushing visual inspection and/or replacement and the 2024 AD (based on more data) only requires oil particulate inspection.  I haven't seen where the 2024 AD supersedes the 2017 AD.  Even if the FAA assumes, the 2017 AD has been complied with by now, most certainly there have been escapes.  

[EricJ]

31 minutes ago, DCarlton said:

I'm planning to reread the two ADs again today along with the SBs, but I'm stumped from a process standpoint as to how to rectify the compliance requirement differences between the 2024 and 2017 ADs.  I believe the 2017 AD requires bushing visual inspection and/or replacement and the 2024 AD (based on more data) only requires oil particulate inspection.  I haven't seen where the 2024 AD supersedes the 2017 AD.  Even if the FAA assumes, the 2017 AD has been complied with by now, most certainly there have been escapes.  

The 2017 AD applies to a smaller subset of engines than the 2024 AD.    You only need to comply (or assure compliance has been done) on your engine for that AD if it is covered by the 2017 AD.   If it is, then you need to comply with the 2017 AD.   You only need to comply with the 2024 AD if it is covered by that, which is a broader category (and a bit more ambiguous), than the 2017 AD.    If you engine is covered by both, you need to comply with both.   Compliance with the first (2017) may be terminating for the 2nd if parts were installed that are not covered by the 2024 AD.  

[DCarlton]

5 minutes ago, EricJ said:

The 2017 AD applies to a smaller subset of engines than the 2024 AD.    You only need to comply (or assure compliance has been done) on your engine for that AD if it is covered by the 2017 AD.   If it is, then you need to comply with the 2017 AD.   You only need to comply with the 2024 AD if it is covered by that, which is a broader category (and a bit more ambiguous), than the 2017 AD.    If you engine is covered by both, you need to comply with both.   Compliance with the first (2017) may be terminating for the 2nd if parts were installed that are not covered by the 2024 AD.  

Makes complete sense from a process perspective.  From a practical perspective though, it appears that they both address the exact same part with the exact same problem; but based on more data, they've relaxed the compliance requirement.  I'm guessing it would be hard for the FAA to now say, the first AD based on limited data was overkill. 

[PT20J]

9 minutes ago, EricJ said:

The 2017 AD applies to a smaller subset of engines than the 2024 AD.    You only need to comply (or assure compliance has been done) on your engine for that AD if it is covered by the 2017 AD.   If it is, then you need to comply with the 2017 AD.   You only need to comply with the 2024 AD if it is covered by that, which is a broader category (and a bit more ambiguous), than the 2017 AD.    If you engine is covered by both, you need to comply with both.   Compliance with the first (2017) may be terminating for the 2nd if parts were installed that are not covered by the 2024 AD.  

I agree with your analysis. But, since the 2017 AD was issued, Lycoming has determined that physical inspection of the bushing(s) can be replaced by inspection of the filter and suction screen. It is difficult to determine what parts are in a field overhauled engine from the “ship date” effectivity used in both ADs. So, it would seem reasonable for the new AD to “supersede” to 2017 AD. 

Unfortunately, no one made that point when the NPRM was issued (how many of us even knew about it?), and now that it is a final rule, the FAA isn’t likely to want to change it. But, I wonder if the FAA might accept the new AD as an alternate means of compliance with the 2017 AD? 

[EricJ]

6 minutes ago, PT20J said:

Unfortunately, no one made that point when the NPRM was issued (how many of us even knew about it?), and now that it is a final rule, the FAA isn’t likely to want to change it. But, I wonder if the FAA might accept the new AD as an alternate means of compliance with the 2017 AD? 

There's a section on ADs that describes whether other ADs are affected, and, unfortunately, 2024-21-02 says "(b) Affected ADs  None".  

Edit:  Petitioning for the 2024 AD as an AMOC for the 2017 AD might be a reasonable strategy.

 

[PT20J]

Interesting comment to FAA from Mike Busch included in the Docket for the original 2017 AD:

FAA-2017-0788-0017_attachment_1.pdf

EDIT: Link to AOPA letter Mike referenced in the above comment.

https://download.aopa.org/advocacy/0803_MSB_letter.pdf

Edited November 3 by PT20J

[MikeOH]

I knew I smelled a rat in this whole debacle; after reading the documents that @PT20J posted I have confirmed that my sense of smell is intact.