Cracks in 3 cylinders IO-550

[RH Galyen]

19 hours ago, Robert C. said:

thanks for input so far, pls keep it coming!

I implicitly trust my shoIp. They haven't tried to rip me off ever, and have a well deserved reputation for competence. The charter operation they are a part off got rid of their Barons because of the frequent cylinder cracking they experienced on those, so they have experience with the issue.

I just authorized them to take those jugs off so they could look at the cams/lifters/etc.

Robert

I worked on 402 Cessnas, used on short hop flights. We always thought the cracked jugs came from shock cooling. We changed out 13 cylinders in one week, 4 different aircraft.

[GeeBee]

3 hours ago, M20Doc said:

Continental seems to take the issue seriously.

In Canada non destructive testing is to be completed by an AMO (CRS) with personnel certified to Mil STD 410.  I’ve never seen one of them use red dye, it’s always been fluorescent penetrant and UV light.

Clarence

I guess I would have to ask. What is the harm in doing an NDT inspection to verify that it is indeed a crack? 

 

[Guest]

2 hours ago, GeeBee said:

I guess I would have to ask. What is the harm in doing an NDT inspection to verify that it is indeed a crack? 

 

None.  We follow up visual inspection with NDT inspection to confirm or deny the finding, but it is done by qualified personnel.

Clarence

[GeeBee]

How often is the visual overturned by NDT in the case at hand?

 

 

[cferr59]

7 hours ago, GeeBee said:

I guess I would have to ask. What is the harm in doing an NDT inspection to verify that it is indeed a crack? 

 

I believe these are the instructions for MSB09-1B which is guidance for the EQ3 cylinders that TCM wanted to replace.   It wouldn't be a good idea to forgo such an inspection if you are on the hook to pay for the cylinders given that it may not be a crack at all!

[Robert C.]

Update: Dye Penetrant Inspection was done and no cracks were found....phew

Thanks everyone for sharing your experiences and recommendations!

Robert

[kmyfm20s]

1 hour ago, Robert C. said:

Update: Dye Penetrant Inspection was done and no cracks were found....phew

Thanks everyone for sharing your experiences and recommendations!

Robert

Nice!

I’m curious did they do it as a result of your inquiry or was it part of their standard procedure? Hopefully it was done before pulling the cylinders. 

[Robert C.]

It was done as the result of a direct request. He'd already made up his mind (based on his past experience) that the cracks were real.

Waiting to hear whether he pulled the cylinders - certainly wouldn't want to pay for that since that could have been prevented if he's done the DPI without my prompting.

[GeeBee]

Yep. Three cylinders cracked in the exact same spot was just a little too weird. Glad you were spared the expense. Happy New Year,

This episode goes straight to the article from Mike Busch I posted. Trust, but verify. The IA in that article was sure it was a crack too, pulled and replaced the jug.. If I may quote:

"I asked whether the shop had performed a DPI to verify the crack before yanking the jug. My friend said he’d requested that, but the IA demurred, claiming it would be a waste of time and adding, “I know a head crack when I see one.” "

Epilogue, the jug was retrieved, tested and found to be crack free. Money had to be refunded.

I learned to verify cracks back in 1980 when a shop told me the spar on the horizontal stab of a T310 was cracked. They refused my request to go further. I pulled the airplane into another hangar, called out an NDT firm who performed an eddy current and guess what? No crack!

 

 

 

[Guest]

I’d be curious what an eddy current inspection would reveal?

Clarence

[PT20J]

1 hour ago, M20Doc said:

I’d be curious what an eddy current inspection would reveal?

Clarence

I don’t know much about NDT. In your experience does eddy current often find real cracks that DPI misses? Just want to make sure I order the appropriate test if the need arises. Thanks.

[Yetti]

6 hours ago, Robert C. said:

Update: Dye Penetrant Inspection was done and no cracks were found....phew

Thanks everyone for sharing your experiences and recommendations!

Robert

It would seem that if it were cracked the crack would start at the base of one of the holes then spread inline to the other hole.   Also seems like there is no oil under there to come up through the crack.   Like someone said was a sharpy or something used to make them black?   Eddy current would seem like a good idea.  But may show the top line.

[GeeBee]

Certainly, eddy current would be the "gold standard" in this case, however you have three cylinders, with three identical "cracks". You would then have to conclude that a DPI failed in all three cases to detect the crack. That seems highly improbable. I would still keep an eye on them for a while, if you see blue stains stop flying it immediately. 

NDT can be problematic even in the best of circumstances. United 232 and Delta 1288 both proved the point, but think how rare the events that occurred in those cases. This can make for good reading on NDT.

https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9801.pdf

Cliff Notes version: 

The Safety Board recognizes that all necessary probability of detection data and crack propagation rates may not be immediately available, and may have to be developed for some components. Therefore, the Safety Board believes that the FAA should require, as an interim measure, pending implementation of Safety Recommendation A-98-19, that critical rotating titanium engine components that have been in service for at least 2 years receive an FPI, eddy current, and ultrasonic inspection of the high-stress areas at the engine’s next shop visit or within 2 years from the date of this recommendation, whichever occurs first.

 

IOW, nothing is guaranteed. Wash, rinse, repeat.

 

 

 

[EricJ]

14 hours ago, PT20J said:

I don’t know much about NDT. In your experience does eddy current often find real cracks that DPI misses? Just want to make sure I order the appropriate test if the need arises. Thanks.

Generally DPI only tells you about the surface condition, i.e., there is a crack at the surface.   Eddy Current testing can characterize cracks below the surface, so is a more informative test for assessing things like this.   Eddy Current Inspection requires not only the expensive equipment, but a reasonably skilled operator to get the full benefit of the testing.

[GeeBee]

I would agree, however if the DPI is triggered by a visual assessment of crack existence, then the crack is sufficient to be evaluated by DPI.

 

[tmo]

18 hours ago, Robert C. said:

It was done as the result of a direct request. He'd already made up his mind (based on his past experience) that the cracks were real.

On a total tangent - amazing how much money, downtime and outright waste (binning three good cylinders) a community such as MS can help save.  Not to mention possible "infant mortality", run-in costs, and aggravation associated with the ordeal.  Go Mooneyspace!

[Robert C.]

18 minutes ago, tmo said:

On a total tangent - amazing how much money, downtime and outright waste (binning three good cylinders) a community such as MS can help save.  Not to mention possible "infant mortality", run-in costs, and aggravation associated with the ordeal.  Go Mooneyspace!

Amen!

[cferr59]

Interesting article from Mike Busch about a similar situation with a much less happy outcome and some comments on the use of eddy current inspections on cylinders.  Makes sense to me that if you can see the crack, then it should fail dye penetrant inspection.

https://www.aopa.org/news-and-media/all-news/2016/july/pilot/savvy-maintenance

"...there’s no guidance from Cirrus or Continental suggesting that eddy current inspections should be performed on cylinder heads. The standard procedure is to inspect the heads visually for cracks, and if a suspected crack is found, to verify that it has significant depth (and is not simply a superficial surface flaw) by performing a dye penetrant inspection. "

"It seemed to me that the much more sensitive eddy current inspection was inappropriate for use on a rough sandcast cylinder head, and was very likely to produce false positives"

[kmyfm20s]

9 hours ago, EricJ said:

Generally DPI only tells you about the surface condition, i.e., there is a crack at the surface.   Eddy Current testing can characterize cracks below the surface, so is a more informative test for assessing things like this.   Eddy Current Inspection requires not only the expensive equipment, but a reasonably skilled operator to get the full benefit of the testing.

We would all get MRI’s for our routine physical exams with that rational.