15AC ACS - Spar Intergranular Corrision

Aeronca Sedan Airplanes
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bwmatz
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15AC ACS - Spar Intergranular Corrision

Post by bwmatz » Mon Dec 15, 2008 15:05

The following communication from the FAA was forwarded to us by H.G. Frautschy with the EAA/Vintage Aircraft Association.

--------------------------------------------------------------------------------
From: Della.Swartz@faa.gov [mailto:Della.Swartz@faa.gov]
Sent: Monday, December 15, 2008 2:27 PM
Subject: Airworthiness Concern Sheet for 15AC


Hello,

I am attaching an Airworthiness Concern Sheet requesting information on
Aeronca Sedan wing spar corrosion. Please disseminate as widely as
possible among sedan owners. We are requesting a response by 1/16/09.

Feel free to contact me at the number below, or by replying to this
email.

Thanks for your assistance, and have a great holiday season.

(See attached file: Sedan ACS.doc)

Della Swartz
Anchorage ACO
voice: (907) 271-2672
fax: (907) 271-6365
-------------------------------------------------------------------------------

The Sedan ACS.doc referred to above has been posted in PDF format at http://www.aeroncapilots.com/SedanACS.pdf
Brian Matz
1946 11AC NC9485E
S/N 11AC-1121
Based @ Barber Airport, Alliance, OH (2D1)
bwmatz11ac@yahoo.com

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Post by joea » Mon Dec 15, 2008 15:39

Had heard that this was coming but was asked to not say anything until it came out.

It would be very interesting to find out how many of those 34 wings that needed spar cap parts were used in harsh conditions, ie on floats in salt water areas. Salt water spray gets almost everywhere on most float planes IMHO and its never good for metal. You can try to wash it off but in my experience you never get all of it out.

Would strongly recommend every Sedan owner inspect your wings as well as you are able for this and if there is any sign of corrosion report it. As well if there is no sign report this as well to get some sort of baseline.

I have already looked at the spars in my wings and found no issues with them. Take the bolt out of the aileron and swing it up and out of the way to gain access to the inside of the wing. If you have a borescope you can snake it forwards to the front wing spar area and inspect part of the area. Also talked with another Sedan owner who used a long inspection mirror in this area in the same manner.

A third Sedan owner told me about removing the forward wing cap next to the windshield and inspecting this area in this manner. He had done this while removing his fuel tank bladders.

We have about 200 Sedans flying in the world right now. Thats 400 wings in the air and the FAA ACS mentions that 34 spar cap angles have been sold and that the seller "estimates that 90-95% of them of them were replaced for corrosion." Would really like to find out how many of these were operated on floats in salt water to see if this is a major part of the problem. If we had to start carving inspection holes in our wings to check this it would be a MAJOR undertaking, somewhat like the "7/11 Aeronca wooden spar inspection" that has been such a debacle to the Chief/Champ owners group.

Joe A

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Spar Cap Intergranular Corrosion

Post by esandberg » Mon Dec 15, 2008 19:31

Hi all,

I'm restoring one of the 15AC projects Brian Safran had, and since I had to replace the skins on my right wing anyway, had a good look at the capstrips with penetrant dye. Nothing is known about this wing's history.

The upper/lower capstrips were pretty bad and I'm not sure I'd have seen the smoking gun with a borescope. Before I used the dye, I thought the little bulges were just quaint little imperfections in the 1940's era metal extrusions. After I started picking at the little bulges with an icepick where the dye was going nuts, it flaked up like splintery, rotten wood.

I still have the capstrips; if anybody wants a chunk I can send you a piece. It might make the borescope process easier if you can compare a known culprit to what you're seeing on the screen.

I also have some good close-up pictures, but it doesn't look like pictures can be posted here. Email me and I'll send you what I have.

Eric
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Post by joea » Mon Dec 15, 2008 19:35

Eric,

Is it only on one wing, and any idea if this plane was ever on floats?

Thanks for the info. You can post photos here but its probably faster to email them to me and I will do it for you. Would love to see them and get them up for everyone to look at.

Thx,

Joe

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Spar Cap Corrosion

Post by bsafran » Tue Dec 16, 2008 06:58

I'm really glad this Airworthiness Concern Sheet came out. Nobody wants an AD issued on their airplane, especially one that requires as much work as installing all of the required inspection holes.

However, it's a simple fact that the Sedan was built with just too few of these inspection accesses. Try getting a birds nest out a wing with just two inspection holes! Their thinking was right at the time of manufacture about not corrosion proofing anything inside the wings. They had no idea that we would still be flying their planes 60 years after they rolled off the assembly line.

While all of the Sedan owners are probably singing the blues right now, how would they feel if we didn't have someone supporting the 15AC type certificate and making the parts that will be needed for this repair? If it wasn't for Burl, this AD would likely kill the Sedan. I am sure that when people start looking into their brand new inspection holes, there are going to be a few guys crapping their pants at what they find. I have four sets of wings here. Two are on saw horses with no wing tanks installed so it is easy to confirm that they are okay. I am removing another set to pull out the metal tanks and install them properly.

I am reasonably sure that those spars will be just fine. But I do have a set of spare wings with cap corrosion that is awful and will require a complete tear down and repair. That makes a 25% failure rate. Burl has led me to believe that once you confirm that your spars are fine and you spray them down with a good corrosion proofing, you have solved the problem. The one time wooden spar inspection on the Champs and Chiefs fixed their problem. (I had a cracked spar!)

If anyone has to replace the spar caps in their Sedan wings, that would be the perfect time to upgrade to metal tanks if you still have the bladder type. Then you would have the perfect 4 place taildragger. Don't forget, the 15AC series has one of the fewest number of AD notes of any four place aircraft built.

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Post by joea » Tue Dec 16, 2008 07:57

Brian,

Thanks for the input.

You have 8 wings there and 2 of them have corrosion? Any history on them or where they have been flying?

Bill in Homer has his wings off right now putting new fuel tanks in them and said that his has no issues at this time, but the plane spent much of its life in the Mid-West and from that he knows has never been on floats.

Agree about the inspection ports, but really, really hope that we do not end up having to do what some Chief/Champ people did and put a port in every other wing bay.

Joe

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Post by Grumps » Tue Dec 16, 2008 10:25

I would check the history and see if they had been in or around salt water. Without the history of the wing I wouldn't make any rash decisions.

Doug
Keep the pointed end forward--
The dirty side down.....
And the blue skies on top....

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Post by Matt » Tue Dec 16, 2008 13:53

Maybe just as a reference for a Sedan that, to my knowledge, has never even been on floats and that was based in Minnesota and North Dakota for 53 years. Hangared, most of its life. Still, there are some clear signs of corrosion in a few areas. Mainly where an impressive mouse home was found! But also along the rivet lines of some skin panels and only very slightly on the spar caps. We had the wing open for restoration, replaced the concerned skin panels, brushed the metal clear where only slight surface corrosion was found and treated these spots with a corrosion stopper.

Matt

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Last edited by Matt on Tue Dec 16, 2008 13:56, edited 1 time in total.

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Post by aeroncafan » Tue Dec 16, 2008 13:56

Beechcraft Musketeers had/have a similar problem and it affected the complete section of the spar, not just the caps.
Last edited by aeroncafan on Wed Jan 21, 2009 17:51, edited 1 time in total.

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Post by joea » Tue Dec 16, 2008 18:03

Sorry for the delay, here are Eric's photos.

Image

Removing top cap from the spar. 15AC-253, right.

Image

Top capstrip. Cosmetically about a 6. Didn't scotch-brite anything before dye. Some vestiges of zinc chromate, but nothing substantial. Fair amount of powdery surface oxide.

Image

Applying penetrant dye

Image

After applying developer and waiting, typical trouble spot.

Image

Yes that is aluminum crumbling off of the spar.

Image

After giving the developer 30min. Bulges were just barely visible before dye+developer.

Image

Crumbles/shreds easily. Used an icepick, but could have used fingernail

Image

Icepick rips it up like a popsicle stick

The comments are Eric's. He did say that he purchased the wings used and had no idea if they had ever been on a floatplane or not.

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Post by esandberg » Tue Dec 16, 2008 20:00

Thanks Joe!

Correct, nothing is known about the wings I got with this project, other than they were piled up in a storage unit near Toledo for several years, and I removed both wasp and mouse nests from the insides (although not a Trophy Nest, like Matthias...)

They very well could have come from somebody's back yard in Florida, been on floats in San Diego or been sitting on a beach for all I know.

Encouraging for everybody else, perhaps, is how good Matthias' capstrips looked, even with the Mouse Mansion.

Eric
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Post by joea » Tue Dec 16, 2008 20:48

From another Sedan owner:

~~~~

Hi Joe, I inspected the wings today with a bore scope that projects images on a small screen, it has about a 30" reach with a good magnification, I was able to reach almost all of the rear of the front spar, both top and bottom of the spar caps, and stiffeners.

Our wings do not show any sign of corrosion, in fact they seem to be in better condition as far as color and general condition of aluminum related to above subject areas, than a 1968 182 that a friend had for a number of years, the C-182 wings were showing signs of discoloration and pocking, that was arrested by a treatment of ACF.

Now our sedan has almost never been out of the high desert environment
for the last fifty plus years, no floats etc . I will send this information on
to the FAA up in Alaska.

I believe as you do that this is related to the sedans on floats and moisture / salt etc. While the 15AC sedan is new to me I am a A&P and perform all of my own work, our sedan seems to be in good condition, but then of course it has always been hangared.

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Post by Paul Agaliotis » Wed Dec 17, 2008 11:34

I looked into the SDR's and found 1 in CA from 2002. Has there been any accidents related to this problem? If there hasn't I would say that the inspection process currently in place is working. I think a Maintenance Alert is all that would be required.
Paul
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Post by joea » Wed Dec 17, 2008 11:46

Paul,

From what I was told, this was found ONLY after a wing was ripped open while being moved on the road, so no accidents that I know of.

That said, there clearly are some Sedan wings that have problems that need addressing, like those on Eric's photos. I have no problem with a preliminary inspection to check on the wings, but a blanket "drill holes in the wings and put inspection covers on every one" is IMHO a bit much at this stage.

Joe

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15AC wings

Post by 49_sedan » Sun Dec 21, 2008 09:42

I replaced the cap angles on the left wing on #367. Initial inspection through the rear spar holes showed a lot of corrosion throughout the wing. The steel fitting that attaches the strut to the spar was badly corroded. When I got the wing apart the spar did not look as bad as Erics, but the upper angle did have a bad bulge about 1/3 of the way out. As soon as I saw this I realized that the whole angle had to be replaced. The right wing did not have nearly as much corrosion in general and the cap angles appear to be fine. The aircraft was based within 1/2 mile of the Maine coast for at least 15 years. I dont know of the history before that. It seems that the wings were from two different airplanes, the way one was so much more corroded than the other. The fuselage also showed sign of corrosion throughout.

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