Continental Engine AD - Big Troubles?
Hey again all, just been reading about Cirrus grounding their entire fleet until further notice due to an upcoming Continental AD. The part that got me was:
'Continental Aerospace Technologies is working with the FAA on possibly developing an Airworthiness Directive (AD) on aircraft powered by late models of several of its engine models. These include 360-, 470-, 520- and 550-series engines. Continental is urging owners of planes with any of these engines with a manufacturing date between June 1, 2021, and February 7, 2023, to voluntarily ground their planes “until further information is available.' This is an enormous call, particularly as it will ground most aircraft with an engine less than 200 hours old. Keen to see what you all think. Cheers, Mach1 |
just been reading about Cirrus grounding their entire fleet |
Currently dates between June 1, 2021 to February 7, 2023 and with less than 200hrs on the engine. Also applies to OH engines with a new Crankshaft between said dates. The issue is centered around Crankshaft counterweight pins and the circlips that hold them.
looks like a two day mx input to pull a few cylinders and inspect. Brought on by three in service engine failures (not Cirrus airframes). Cirrus were the first manufacturer to break cover and start to ground (or pause, as they called it) their own fleet that fell between the initial dates. The AD will probably give five hours grace to ferry with “essential crew” crew only to a mx shop for checks and rectification. probably those caught up in this already know everything mentioned above. Took a while to tease the actual issue out of Continental. |
You might want to read this AD.
https://www.federalregister.gov/docu...with-a-certain https://www.regulations.gov/docket/F...-0027/document |
Originally Posted by Cyclic Hotline
(Post 11384020)
You might want to read this AD.
https://www.federalregister.gov/docu...with-a-certain https://www.regulations.gov/docket/F...-0027/document |
Originally Posted by Cyclic Hotline
(Post 11384020)
You might want to read this AD. https://www.federalregister.gov/docu...with-a-certain
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Originally Posted by wrench1
(Post 11384059)
FYI: this is not the AD in question for the OP issue. There is no AD currently in the works but an SB in the works which will contain S/Ns. TCM came out with a notice yesterday. Word is supposedly the retaining rings/circlips for the crankshaft dampener bushings/pins were orientated opposite of the installation requirements. If you want to see the area in question look in the old SB 99-3 which addressed a different issue. Given they have it narrowed down to less than 200 hrs TIS engines they probably have a good idea of what is the cause. Regardless, my guess there more to this than a reversed circlip as most have no specific orientation requirements.
So, it could be, one specific mechanic did install the circlips consequently the wrong way around, and it seems to be known from experience, that the engine destroys itself within 200 TIS, when the circlip(s) is/are mounted wrongly. Retrieve the engine serials this mechanic worked on, follow the delivery trail, and it is known which engines need to be opened up and potentially will need a crankshaft rebuild/revision. A complication can be, that crankshafts might be prebuilt/assembled, leaving the challenge, which crankshaft ended up in which engine. An issue is to reliable reach all aircraft owners/users with affected engines. |
Originally Posted by WideScreen
(Post 11384086)
The circlip seems to have a "sharp" and a "non-sharp" edge,
Mount it the other way around, and it'll probably get some slack, |
While they might possibly exist, I've never encountered a circlip that came with instructions regarding which way round it should face.
Presumably if they do, they would have to feature some unambiguous marking on one face, or have some other asymmetry so that the correct orientation could be guaranteed. Sounds a tad unlikely to me. |
Originally Posted by DaveReidUK
(Post 11384137)
While they might possibly exist, I've never encountered a circlip that came with instructions regarding which way round it should face..
https://cimg7.ibsrv.net/gimg/pprune....3af90dcae5.jpg |
Is it just me or does that diagram make it look like the rounded side is outboard?
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Originally Posted by MechEngr
(Post 11384156)
Is it just me or does that diagram make it look like the rounded side is outboard?
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Originally Posted by MechEngr
(Post 11384156)
Is it just me or does that diagram make it look like the rounded side is outboard?
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Originally Posted by wrench1
(Post 11384135)
It does and is a result the stamping manufacture process. Common AN/NAS steel washers have the same feature. Supposedly the weight pin retainer plate is stamped also. One theory is the sharp side of the clip and the sharp side of the retainer plate may cause interference and prevent complete seating of the clip. However the clip ear dimension check should have caught that, if it was checked.
The important aspect in this is, the manufacturer documentation explicitly mentions the way the circlip needs to be mounted. I think, the clip ear dimension check/spec is there to have an extra check, whether the circlip is mounted correctly. Though, a precise mechanic might have used "force" to enforce the proper clear ear size.
Originally Posted by wrench1
(Post 11384135)
The groove dimension is spec to the clip thickness. Either way there should be no play unless not seated. Plus theres a note that the retainer plate should not have any play at the pin. Perhaps when the SB is released it will provide more on the reason.
The no-play remark for the retainer pin suggests, the mounting of the circlip creates maybe a somewhat spring-loaded construction, to have the whole in the normal situation "without play". Another argument, to have the sharp edge of the circlip on the outside and being forced somewhat into the groove, together with the clip ear spec to check on this. Temperature effects to be seen, though. The SB/AD would be an interesting one. |
Originally Posted by WideScreen
(Post 11384175)
Yes, maybe, this is a special spec circlip.
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Originally Posted by DaveReidUK
(Post 11384137)
While they might possibly exist, I've never encountered a circlip that came with instructions regarding which way round it should face.
Presumably if they do, they would have to feature some unambiguous marking on one face, or have some other asymmetry so that the correct orientation could be guaranteed. Sounds a tad unlikely to me. |
Originally Posted by wrench1
(Post 11384210)
These clips are standard and cost about $0.70 USD each. Nothing special about them. The ring grooves and retainer plates are checked as part of overhaul with the bushings changed as well. Usually one buys a ring kit for OH and gets new circlips for this application.
Originally Posted by ShyTorque
(Post 11384265)
I’ve been rebuilding engines (mainly air cooled motorcycle types) since the early 1970s and have always been aware that the side of a circlip with the sharp edge should be the thrust bearing side. They don’t come with instructions! A good example is those holding gudgeon (wrist) pins in pistons. The last thing you need is a loose clip and the end of the pin scraping the bore. The rounded edge of the circlip can ride up the (square edged) groove and pop out the same way it was incorrectly put in. Wire circlips are different in that they have rounded grooves.
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For decades mechanics knew how to install circlips the right way. And a FAA approved SB drawing from 1999 shows it in the wrong direction.
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Just a pilot, fix a lot of things around the house. Having a clip that fits both ways, no obvious markings or instructions what the correct way is, and the engine blows up within 200 hours if you do it wrong sounds like an unacceptable risk.
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Maybe it’s just that some less experienced engineers/mechanics these days (possibly a very small number) don’t have certain basic “nouse” about what’s right and what’s not.
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Yes but if this makes a SEP quit in the first 200h then there is something serious wrong with the construction or the mechanic education. My view is that the construction is flawed and they kicked for 50 years the can down the road, The SP is from 1999 and described the same problem as they have now.
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FWIW: its more than just a single mechanic failure as there is a QA system that failed also. So it will be interesting to see if the forthcoming SB will explain what happened.
That said, all rings/clips have a sharp side and a round side. However, some have an additional 10 deg bevel on the round side and fall under different specifications and part numbers. The beveled rings need a corresponding beveled/chamfered groove to be installed hence the specific direction. In general, non-beveled rings/clips have no specific install orientation as the grooves are uniform. But all are still considered standard parts. Regardless, if the ring was beveled and installed backwards then it would have also failed the minimum ear gap check of .179 “ as well. So not one but 2 failures in the system. And with 50+ years of no ring/clip failures its not a design issue but unfortunately a human issue. FYI: the SB 99-3 I linked above has zero to do with this issue. The SB corrected a bushing install problem not a ring problem which was causing cracks in the crank. I used it strictly because it had pics of the same area. |
MSB 23-01, Crankshaft Counterweights has been released.
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Really confused - is the snap ring groove really not uniform in depth all the way around? Also, is there a line that should not be there? The pin should also block the view of the far side of the counterweight in the gap.
https://cimg9.ibsrv.net/gimg/pprune....ce4789f499.png |
Originally Posted by MechEngr
(Post 11385346)
Really confused - is the snap ring groove really not uniform in depth all the way around? Also, is there a line that should not be there?
I believe the line you refer to is part of the weight itself as shown in SB picture. The pin is not that wide. |
I have never seen an offset depth in any snap ring application guide for any type of snap ring. Even if one did, the ring isn't guaranteed to be locked into position so any offset preference could be disaster.
That part of the weight is slot. That horizontal line segment should bridge where the two horizontal segments are separated above the pin. I know the pin isn't that wide; that's why I think it's wrong. In vertical order there are are two large top flats, two smaller slot flats, the top edge of the bushing bore, which is below the two smaller slot flats, and then the top edge of the pin. Because of the slot, there is not a complete bore where the bushings are set, so there is no horizon line in that gap. I looked at the old notice - the slot goes all the way through - there should not be material sectioned in the middle. This matches the hidden lines in the overall face view. Perhaps they need to hire someone with drafting experience. |
Originally Posted by MechEngr
(Post 11385362)
I have never seen an offset depth in any snap ring application guide for any type of snap ring.
https://www.rotorclip.com/cat_pdfs/vho.pdf Perhaps they need to hire someone with drafting experience. |
Here's what I think it should look like -
https://cimg8.ibsrv.net/gimg/pprune....85d881577d.png Seems like large (any) errors in maintenance diagrams should be a huge concern. Notice in that snap ring dimension chart that depth is uniform even though the ring section isn't. Example the -165 has a bore diameter of 1.653, a ring groove diameter of 1.773, and a depth of .060 = (1.773-1.653)/2 |
Originally Posted by ShyTorque
(Post 11384265)
I’ve been rebuilding engines (mainly air cooled motorcycle types) since the early 1970s and have always been aware that the side of a circlip with the sharp edge should be the thrust bearing side. They don’t come with instructions! A good example is those holding gudgeon (wrist) pins in pistons. The last thing you need is a loose clip and the end of the pin scraping the bore. The rounded edge of the circlip can ride up the (square edged) groove and pop out the same way it was incorrectly put in. Wire circlips are different in that they have rounded grooves.
The following steps outline the process for installing internal circlips:
ref - https://uk.rs-online.com/web/content...circlips-guide Not clear to me if there is agreement here or disagreement. I've worked on a few motor cycle engines (mostly BSA 650) and a few car engines and gear boxes. I don't think I ever paid any attention to circlip facing direction but I always ensured they were fully seated. The TCM mandatory service bulletin does not require removal of circlips to check face orientation. It only requires a check for seating and angular orientation. They don't seem to think face orientation is important. |
Originally Posted by MechEngr
(Post 11385375)
Notice in that snap ring dimension chart that depth is uniform even though the ring section isn't.
Originally Posted by EXDAC
(Post 11385378)
The TCM mandatory service bulletin does not require removal of circlips to check face orientation. It only requires a check for seating and angular orientation. They don't seem to think face orientation is important.
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Originally Posted by wrench1
(Post 11385678)
My guess is if the ring was not facing the proper way it will fail the gap test which does require removal and replacement of the ring per the SB.
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I have never seen a tapered groove for a snap ring. I have seen semi-circular grooves for formed wire retainers.
The main problem that appears to be this case is if the person installing the ring thinks that just because they have pushed the ring into full flat contact with the item being retained that the ring must be in the groove. Given the spring load the ring will be wedged into the bore and appear to be secure, but if one doesn't look to see then this situation can certainly occur. |
Originally Posted by MechEngr
(Post 11385713)
The main problem that appears to be this case is if the person installing the ring thinks that just because they have pushed the ring into full flat contact with the item being retained that the ring must be in the groove. Given the spring load the ring will be wedged into the bore and appear to be secure, but if one doesn't look to see then this situation can certainly occur.
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Originally Posted by MechEngr
(Post 11385713)
I have never seen a tapered groove for a snap ring. .
Originally Posted by EXDAC
(Post 11385708)
Is there any suggestion that the groove/register is not rectangular section?
https://cimg6.ibsrv.net/gimg/pprune....5b6d66f706.jpg |
FAA AD has been issued.
AD 23-04-08 |
OK - Now I've seen one. Interesting. Google finds no cross reference to the TCM number.
I found the MS16631 document on quicksearch.dla.mil ; still Active. INTENDED USE- TO PROVIDE SHOULDERS FOR POSITIONING AND RETAINING MACHINE COMPONENTS IN HOUSINGS. TAPERED DESIGN PRINCIPLE PERMITS RINGS TO MAINTAIN PRACTICTICALLY (sic) CONSTANT CIRCULARITY. THE RINGS WITH BEVEL ON OUTER CIRCUMFERENCE WHEN SPRUNG INTO GROOVE WITH TAPERED OUTER WALL CORRESPONDING TO RING BEVEL WILL SELF ADJUST AND PROVIDE SECURE PRESSURE FIT AXIALLY TO TAKE UP END PLAY. THE USE OF THE FOLLOWING FORMULAS ARE BASED ON THE FACT THAT THE RING MATERIAL WILL NOT FAIL IN COMPRESSION I think the instructions would mention a taper as 100% in the axial pressure application a backwards ring would not seat, while a regular ring can partially seat either way. It would be nice to see that cross reference. I can understand why the engine company would "hide" an underlying number. The company I worked for did this with commercial parts; the cynical view is that we got to sell parts with some markup, but the practical side is our internal document also included the exact companies that the parts could be sourced from. Yeah, there were trust issues that limiting to certain vendors made manageable. Too many ways for counterfeit items to get into the supply chain. It was also useful to see what the user (DoD) was up to - they start ordering a lot of some part and we know exactly what it goes into and try to figure out if something has gone wrong - usually a problem with maintainers (like this situation) but possibly some other design or manufacturing issue. Edit: Looking closer, the smallest MS16631 is for a 1.00 inch ID, which is far larger than this application. |
FYI: FAA has decided to supersede the original AD 2023-04-08 with AD 2023-05-16. The "new" AD adds several more engine models, clarifies the SFP requirement, adds a flow chart, and a few other minor changes. The AD will be published tomorrow but here is a final draft version: AD 2023-05-16
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