Continental Engine AD - Big Troubles? [Archive]

Mach1Muppet

11th Feb 2023, 02:35

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

India Four Two

11th Feb 2023, 08:17

just been reading about Cirrus grounding their entire fleet

Not the entire fleet. As you quoted, just aircraft with engines manufactured between June 1, 2021 and February 7, 2023 and it is currently a "voluntary" grounding.

29_Grass

11th Feb 2023, 09:48

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.

Cyclic Hotline

11th Feb 2023, 11:48

DaveReidUK

11th Feb 2023, 12:07

You might want to read this AD.

https://www.federalregister.gov/documents/2023/02/02/2023-02152/airworthiness-directives-continental-aerospace-technologies-inc-reciprocating-engines-with-a-certain

https://www.regulations.gov/docket/FAA-2023-0027/document

I noticed that, but it refers to a much shorter period of manufacture - only valves produced for a few months of 2022, so it's unlikely (though not impossible) that those could be flying on aircraft built in 2021.

wrench1

11th Feb 2023, 13:47

You might want to read this AD. https://www.federalregister.gov/documents/2023/02/02/2023-02152/airworthiness-directives-continental-aerospace-technologies-inc-reciprocating-engines-with-a-certain

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 (https://www.continental.aero/Potential-Safety-of-Flight-Issue.aspx) 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 (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiPjvvP2o39AhUjk2oFHVAdBLQQFnoECAsQAQ&url=http%3A%2F%2Fwww.tcmlink.com%2Fpdf2%2Fmsb99-3c.pdf&usg=AOvVaw0YQspO7AynH6kCgYVGvN01) 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.

WideScreen

11th Feb 2023, 15:19

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 (https://www.continental.aero/Potential-Safety-of-Flight-Issue.aspx) 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 (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiPjvvP2o39AhUjk2oFHVAdBLQQFnoECAsQAQ&url=http%3A%2F%2Fwww.tcmlink.com%2Fpdf2%2Fmsb99-3c.pdf&usg=AOvVaw0YQspO7AynH6kCgYVGvN01) 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.
The circlip seems to have a "sharp" and a "non-sharp" edge, where the sharp edge needs to be positioned "outwards", according SB 99-3. Mount it the other way around, and it'll probably get some slack, in the long run loosening up the balance weight mounting, in the end, destroying the engine, once one of the balance weights departs its mounting.

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.

wrench1

11th Feb 2023, 16:40

The circlip seems to have a "sharp" and a "non-sharp" edge,
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.
Mount it the other way around, and it'll probably get some slack,
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.

DaveReidUK

11th Feb 2023, 16:46

wrench1

11th Feb 2023, 17:25

While they might possibly exist, I've never encountered a circlip that came with instructions regarding which way round it should face..
The circlip won't have those instructions as they are considered a standard part. Its the aircraft maintenance instructions that will dictate that orientation as it does for this weight pin installation as shown below. Most clip installs are not direction specific in my experience. Even standard washers may have an install requirement by the OEM whether the smooth or sharp side faces one specific direction. There's also no mark on the clip as one can tell by feel or sight which side has a sharp edge or round edge quite easily.

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/487x397/clipx_3b86f238e6d3eef869645ef27b136f3af90dcae5.jpg

MechEngr

11th Feb 2023, 17:32

Is it just me or does that diagram make it look like the rounded side is outboard?

WideScreen

11th Feb 2023, 17:43

Is it just me or does that diagram make it look like the rounded side is outboard?
Looks like, though, I think, that "rounded thing" visible is part of the balance weight "behind" the plain of the diagram. To give it a kind of 3D appearance.

wrench1

11th Feb 2023, 17:59

Is it just me or does that diagram make it look like the rounded side is outboard?
We thought the same. But if that was the case then it should have been black below the "diagonal" line. However, it could have been mistaken by the person installing the clips?? The larger picture associated with this close up doesn't show that line. The full diagram is in the SB 99-3 link above.

WideScreen

11th Feb 2023, 18:07

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.
Yes, maybe, this is a special spec circlip. I could even imagine, the "rounded" side is extra rounded to match (or to avoid damaging) a rounded edge on the inner-inside of the groove. A rounded inner-side edge to avoid a sharp edge and a potential fatigue starting point.

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.
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.
When you have mating mechanical parts like the groove/circlip, these either have some play, or are tightly connected. And, when there is (a little, microns) play and a lot of force, eventually, the play will get bigger.

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.

wrench1

11th Feb 2023, 19:46

Yes, maybe, this is a special spec circlip.
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.

ShyTorque

11th Feb 2023, 21:53

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.

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.

WideScreen

12th Feb 2023, 02:37

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.
Probably, though the mechanic might have applied "general" knowledge (nothing special) and now, we do have panic, including ac/incidents, around these engines, focusing on the circlips.
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.
For this engine, it got explicitly specified. Probably not to nag the mechanics, but because of genuine reasons, which could be the reasons you specify or maybe additional ones. I've seen so many detailed instructions, thinking "why the hell do like that", though sometimes finding out later, there were genuine reasons to do so. So, for me, manufacturer instructions are the leading instructions.

EDLB

12th Feb 2023, 20:28

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.

hans brinker

13th Feb 2023, 00:11

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.

ShyTorque

13th Feb 2023, 09:02

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.

EDLB

13th Feb 2023, 11:20

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.

wrench1

13th Feb 2023, 16:44

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.

wrench1

13th Feb 2023, 19:05

MSB 23-01, Crankshaft Counterweights (http://www.tcmlink.com/pdf2/MSB23-01.pdf) has been released.

MechEngr

13th Feb 2023, 22:44

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.org-vbulletin/460x480/snap_ring2_27174df07e4e6bb061ee97b6d45b15ce4789f499.png

wrench1

13th Feb 2023, 23:09

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 groove won't be uniform depth if a beveled ring/clip is called for. The groove would require a matching chamfer/bevel and is the reason a specific orientation is called for. I can find no cross-reference to see if the TCM ring P/N is beveled. Non-bevel rings normally use a uniform groove.

I believe the line you refer to is part of the weight itself as shown in SB picture. The pin is not that wide.

MechEngr

13th Feb 2023, 23:27

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.

wrench1

13th Feb 2023, 23:44

I have never seen an offset depth in any snap ring application guide for any type of snap ring.
Here's one reference. As I mentioned, if the ring is reversed it will not match the groove and will not meet its minimum engage measurement which was also missed during the assembly. The fact they are using Go-No Go gages to check that engagement measurement shows this point.
https://www.rotorclip.com/cat_pdfs/vho.pdf
Perhaps they need to hire someone with drafting experience.
Keep in mind these are not engineering diagrams but maintenance work aids. The written note to orientate the ring takes precedent. If you look hard enough you'll find this issue to be a "feature" of many maintenance diagrams.

MechEngr

13th Feb 2023, 23:54

Here's what I think it should look like -

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/460x480/snap_ring3_e87268c461c64531113a7e67073c9185d881577d.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

EXDAC

14th Feb 2023, 00:07

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.

"How to Install Internal Circlips
The following steps outline the process for installing internal circlips:

Begin by choosing a pair of internal circlip pliers which fit into the circlip end holes
You should then fit the plier tips into the holes on the ends of the retaining ring to be installed
Squeeze the handles to close the circlip plier handles and contract the circlip to the desired size
Guide the ring into the circlip groove and release the pliers

Once again, it is important to take the smooth and rough sides of the circlip into account when completing the installation. Internal circlips should always be installed with the smooth side facing the part and the rough side facing outwards in order to help guard against the possibility of damage."

ref - https://uk.rs-online.com/web/content/discovery/ideas-and-advice/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.

wrench1

14th Feb 2023, 13:20

Notice in that snap ring dimension chart that depth is uniform even though the ring section isn't.

I guess it depends on your point of view. Uniform depth to me is same groove depth across the thickness of the ring, i.e., the ring can be installed to same depth regardless of orientation.

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.

Once installed the ring ear gap measurement comes into to play and the face position is moot at that point. The "sharp" face is simply a means to tactilely determine which ring face is which prior to install. 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.

EXDAC

14th Feb 2023, 14:28

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.

I see no reason to assume that. If the circlip groove/register has a rectangular section I would expect the circlip to seat just the same with either face towards the weight. Is there any suggestion that the groove/register is not rectangular section?

MechEngr

14th Feb 2023, 14:32

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.

EXDAC

14th Feb 2023, 15:33

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.

That is my assumption too but I have never worked on this crankshaft assembly.

wrench1

14th Feb 2023, 18:02

I have never seen a tapered groove for a snap ring. .
They're not common, but there are beveled snap ring applications out there. As I recall they were used mainly where the retained part was submerged in oil, fuel, or other lubricants. I don't know if this specific installation uses them but if you have access to MIL-SPEC cross-reference tables for TCM parts we can put this topic to rest. TCM P/N: 62104 retaining ring. The applicable spec will be MS16625 internal ring, basic or MS16631 internal ring, beveled.
Is there any suggestion that the groove/register is not rectangular section?
Don't know. As noted above if a beveled ring is used in this installation the groove will have a 15 deg taper to match the ring, i.e., the bottom of the groove will be narrower than the top. Just a guess as to why the ring didn't seat. Regardless, if the minimum ear gap wasn't checked by the installer doesn't matter what the groove profile is.

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/141x169/untitled_9862a3cca4d79b36fe49e028cca1005b6d66f706.jpg

wrench1

23rd Feb 2023, 14:51

FAA AD has been issued.
AD 23-04-08 (https://drs.faa.gov/browse/excelExternalWindow/FR-ADFRAWD-2023-03796-0000000000.0001)

MechEngr

23rd Feb 2023, 20:09

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.