Carry-thru spar corrosion

[mirobot200]

Oh boy. I think I put the first nail on my plane's coffin... Looking to fix a tare in the headliner zipper today, I noticed what looks like pitting corrosion on a section of the rear carry-thru spar. Some of the other parts of the structure and skin don't look good either. I can't believe this was not caught during the annual a few months ago.

I'm going to get an AME to look at it next week. Does anyone here have any experience with corrosion such as this, and what the prognosis could be? Being primary structure with pitting corrosion, I have a feeling I'll be parting out a Cessna 150 very soon.

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[photofly]

Find an airframe specializing AMO.

[Heliian]

you would think that they could have at least put some primer on the structure, geez that looks rough. Also, that white pulley looks to not be in safety.

The corrosion will have to be removed, which may remove too much material to keep it serviceable.

[photofly]

Alternatively, there’s always Scotchbrite

[mirobot200]

Find an airframe specializing AMO.

There happens to be an AMO at the airpark that rebuilds airframes, so I'll be talking to them next week.

you would think that they could have at least put some primer on the structure, geez that looks rough. Also, that white pulley looks to not be in safety.

No kidding about the lack of primer. Thanks for pointing out that pulley, added that to the list.

Thanks for the replies.

[boeingboy]

Doesnt look too bad.....see it all the time on older Cessna. It needs to be blended and inspected, but not necessarily a death sentance

[mirobot200]

Doesnt look too bad.....see it all the time on older Cessna. It needs to be blended and inspected, but not necessarily a death sentance

Fingers crossed. I took the headliner and some interior trim off today so they can inspect the whole carry-thru structure. There was water dripping from the anchor nuts in the front spar, where the visors bolt through... Not sure how they could clean and inspect the inside of the spars, maybe take a wing off.

[boeingboy]

Ideally the wings come off and you pull out the spar bearing blocks. I think your getting to carried away with yourself right now though.

You could get a borescope in there without taking off the wings but if you don't see corrosion on the outside where it rivets to the ceiling - your more than likely ok.

And GET RID OF THAT FIBERGLASS INSULATION!!!!
That is what hold moisture against the skin and causes problems.

[mirobot200]

Ok thats good to know. At least it will be a good peace of mind to have that whole area inspected. It looks like the headliner hasn't been off in decades. I was curious if that insulation was even needed. It was very damp and disgusting in there when I took it out.

[Dash8-400]

this doesn’t look so bad! Just needs to be blended with scotch brite and do a measurement after. Check the manuals there must be a pile of generic blended repairs for this section of spar. You’ll get a new measurement and then serviceable measurement. Hopefully your between . Then alodine and prime, your in business.

[PilotDAR]

Two thoughts:

Check the manuals there must be a pile of generic blended repairs for this section of spar.

"The manuals" are not explicit, nor provide quantitative tolerance for this type of corrosion damage. I agree that the corrosion in the photo does not appear serious, and probably needs only clean up and corrosion protection as mentioned, rather than part replacement. Though finding "data" to permit such repair, may not be quite so easy....

AC43.13-1B, Chapter 6 contains good information, though may not be in, and of itself, the required data for the return to service.

And,

Though not a factor in flight safety, this reader appreciates the effort put into posting with good grammar....

[Dash8-400]

PilotDAR. Once again, the poster is looking for feedback on solutions to solve his issue about corrosion not pilot commentary.

Manuals/ repair data come in a few forms:

Approved, acceptable and specified as per cars 571.

Once again you want to check the AMM, SRM ECT first before using the AC43.13. Also you can contact Cessna and get RDS and ect.

There are many many generic repairs orders over the years as thjs is a common issue. There’s verbage many times in chapter 50s how much you can blend of a thickness.

Pilot dar my apologies that my grammar offends you and hope you can carry on driving bus with out my grammar effecting your career or the autopilot flying the plane safely!

[groncher]

Dash8-400. If i were the original poster, I would heed any advice given by PilotDAR, his feedback is quite accurate.
He has proven to be one of the most knowledgeable and informative posters here, time and time again, in both maintenance (thus the DAR portion of his name) and flying topics. You should go and look at some of his posts.
Your points for references are valid provided you are working on a larger aircraft... not sure you have seen an AMM or SRM for a C150...not a lot of info there.

[PilotDAR]

Thank you Dash8-400, I appreciate your courtesy. To each their own with the style of posting, I know that there is a new style, where whole words and precise grammar are less the focus. I still appreciate the effort of those who put the extra effort in to writing, just as they would put the effort toward a smooth landing every time. But... thread drift, I admit it...

When I worked for deHavilland back in the day, and was associated with the Dash 8-100, there was of course lots of maintenance information created to enable repairs, including corrosion damage. So, using DHC/Viking manuals as a reference, there would be a good entry point for corrosion repair - for those types. When I worked in the Maldives with Twin Otters, I was very impressed on how TMA handled corrosion - a necessity for them! Corrosion repair data was created as it was required.

Cessna, particularly for the legacy planes, did not provide much structural repair data - some, and more than other manufacturers, but not enough by today's standards. I doubt that Cessna envisioned their legacy models lasting long enough to need quantitative corrosion repair data. I attended a Cessna aging aircraft seminar in Wichita many years ago, Cessna offered updated wisdom on this, though more "watch out for this" as opposed to "here's what to do about it". It's an issue. Recently, I've been called upon to approve C 210 spar repair/replacement resulting from corrosion. Cessna has awkwardly provided data of limited use for this more critical situation, primarily in response to an accident and resulting AD on those spars. Interestingly, in April, Cessna (Textron) commented to the FAA that the 210's were never equipped with the glues on foam (which is a major factor in the corrosion) when the 210's left the factory - yet it's mentioned in the Cessna Service Letter for the 210 spar inspection! The 150 is far back in Cessna's concerns for more detailed repair data - their focus would appear to be on the 172/182/206 next.

The OP has, what appears to me to be, a minor problem, with a not so clear solution, and their question is fair. If there were data directly applicable to this defect on this airplane, I would expect that someone would have presented it by now. I've looked, and I don't see it in the Cessna Service Manual for the 150 - but I agree, in a perfect world, Cessna would have put it there.

Mirobot, which model is your 150?

[Dash8-400]

I have worked on many c150/c152 and c172. I have seen the manuals numerous times and they are lacking information compared to the bigger planes yes.

I always disagree with using the AC43.13 unless it’s last option. Exhaust all options before using that general repair book.

Once again going back to cars 571 :

Check approved data first: AMM if there’s an SRM, ect..

Acceptable data: AC43.13. It’s a great book but very generic.

Specified data: You can always call Cessna and get guidance or see if they have done a generic guideline for this type of corrosion.

There’s a reason they want you to use this flow to do repairs.

Once again if all fails here is a link to chapter 6 AC43.13.13 :

http://raanz.org.nz/techproject/FAA%20A ... r%2006.pdf

This is very generic but can help you evaluate the corrosion and what you can do to treat the corrosion.


Regards ,

Dash8-400

[Dash8-400]

PilotDAR from what I read about you AME experience , you worked on planes in the 1980s / 1990s before the cars were even introduced . When it was okay to sign aircraft fixed instead of corrosion treated IAW .... and have to use references and data to sign aircraft.

The dash market has changed. There’s limits for everything in the SRM, and if not you get go on the website and they have generic repairs for all items. Same with the twin otter market has changed to as mentioned above.

https://support.cessna.com/custsupt/csu ... wlogin.jsp

You can get repair documents on here and if not call Cessna and they will help you find it or guide you to the repair or information.


Once again tread drift, we have came to the same conclusion. It doesn’t look that bad. Will need corrosion removal, then alodine prep paint. Just depth of corrosion will need to be assessed afterward to material left.

[PilotDAR]

After a bit more digging, 'cause I got more curious, I have found in the Cessna SID for the 150 (1969 to 1976) the following corrosion repair criteria:

(6) All the corrosion that you can repair in the allowable damage limits, (less than 10 percent of the
part thickness) is Level 1 corrosion.

Which I interpret as Cessna allowing up to 10% of the material thickness to be removed while dressing out corrosion. However, it would be a good idea to read and entirely understand the SID before invoking it....

PilotDAR from what I read about you AME experience , you worked on planes in the 1980s / 1990s before the cars were even introduced .

Yes, I have worked on GA planes and helicopters since the late '70's, and to this day. My work is not generally maintenance releases, but rather issuing design and repair approvals (STC's and RDA's).

[Dash8-400]

PilotDAR I have done some research and found this inspection criteria for carry-thru spar inspection:

4. INSPECTION INSTRUCTIONS
A. Remove headliner and interior items necessary to gain access to the front and rear carry-thru structure.
B. Visually inspect front spar carry-thru area for loose or missing rivets or corrosion, especially between the spar channel and reinforcement, between the spar channel and upholstery retainer and between the door post bulkhead attachment fittings and the spar channel. Refer to Figure 1.
(1) Clean area before inspecting if grime or debris is present.
C. Visually inspect rear spar carry-thru area for loose or missing rivets or corrosion, especially between the door post bulkhead attachment fittings and the spar channel.
(1) Clean area before inspecting if grime or debris is present.
D. Inspect for corrosion at the wing attachment fittings, lugs, and spar blocks. (1) Clean area before inspecting if grime or debris is present.
NOTE:
3. PURPOSE
5. ACCESS AND DETECTABLE CRACK SIZE ACCESS/LOCATION
Cabin Interior Section
6. INSPECTION METHOD
Visual
7. REPAIR/MODIFICATION
DETECTABLE CRACK SIZE
Not Allowed
A. Clean any corrosion products. The recommended procedure to remove corrosion is by hand sanding, using a fine grained sandpaper.
B. Use 180 or finer grit abrasive cloth to produce a diameter-to-depth ratio of about 10:1. Use ultrasonic methods to determine thickness after removing corrosion. Repairs are required if thickness is less than 90% of uncorroded material.


Like I mentioned before. Guess where I found this? Cessna manuals.


1- will have to figure out metal thickness before
2- grind corrosion
3- figure out thickness post corrosion removal
4- protect and prime if in limits.
5- if not contact Cessna for a repair.

If so work carried IAW Cessna manuals and good to release.

[Dash8-400]

PilotDAR only thing to add to your inspection criteria is that NDT will be required to check thickness post corrosion removal . Also 10:1 aspect ratio for removal of corrosion

[Dash8-400]

Dash8-400. If i were the original poster, I would heed any advice given by PilotDAR, his feedback is quite accurate.
He has proven to be one of the most knowledgeable and informative posters here, time and time again, in both maintenance (thus the DAR portion of his name) and flying topics. You should go and look at some of his posts.
Your points for references are valid provided you are working on a larger aircraft... not sure you have seen an AMM or SRM for a C150...not a lot of info there.

Groncher as you see with many of these posts, and once again I wish I was more active on here to help others with similar issues like this. Unfortunately I am busy a lot. As you see many haven’t touched or delt with manuals in years or have an understanding of the cars as they change a lot. As mentioned before PilotDAR I agree seems to know his stuff and you can tell he works actively on aircraft. As you will notice turning wrench before the cars and post cars lots have changed. How you get data, what data you can use and it’s a lot more regulated then say 30 years ago.

This is where you want you to used approved or specified data before acceptable aka AC4313. Between the both of us we have came with an exact solution for this issue with documents from Cessna to fix this. I respect PilotDAR and he seems to be the only other one commenting on here with knowledge on type and decent information to help this gentleman out.

Mirobot200 so the inspection of this area is called out initial in 2 forms:

Heavy corrosion : 10 years initial
Repeat every 5

Light corrosion: 20 years
Repeat every ten.

So this is why you wouldn’t really look on the annual