Treat minor filiform corrosion

DesertNomad

DesertNomad

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DesertNomad
I noticed this on the belly today... could well have been there since I bought the plane two years ago. What is the best way to treat this... or should I do anything at all? I assume it is filiform corrosion but I guess it could be just a paint bubble.

The plane was in central Texas and now it is in Nevada... very low humidity here.

As you can see, it is not much bigger than a rivet head.

IMG_2881.jpg
 
Filiform has a worm like appearance under the paint. You can't leave it like that, even if it's just bubbled paint it will invite corrosion which it appears has already begun. Follow manufactures manual, which will be: corrosion removal, determine if remaining material thickness is within limits, treat, prime and paint.
 
I looked at some pictures from last annual (October) and it was there then as it is just a few inches from where an antenna was removed. My A&P said nothing about it. In this picture the light make the relief seem thicker than it really is. I'll have another shop look at it.
 
If it were mine, I'd carefully remove the bubbled paint (preferably with a sharp nonmetallic scraper) and see what ya got. I've seen spots like that, that were corrosion and on the rare occasion not corroded.
 
DesertNomad said:
I looked at some pictures from last annual (October) and it was there then as it is just a few inches from where an antenna was removed. My A&P said nothing about it. In this picture the light make the relief seem thicker than it really is. I'll have another shop look at it.
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He may not have noticed it, thus no mention of it. Or he might not have known what it was, if he has only worked in an area of the country with few corrosion concerns.

Regarding your situation. It looks like the corrosion is next to a joint where two pieces of material overlap. Removal of the corrosion you can see may not be enough. It may extend into the joint. Is this possibly in the exhaust trail area?

I'd address the situation now rather than letting it fester. It isn't going to get any better by ignoring it.
 
mondtster said:
Regarding your situation. It looks like the corrosion is next to a joint where two pieces of material overlap. Removal of the corrosion you can see may not be enough. It may extend into the joint. Is this possibly in the exhaust trail area?
Click to expand...

It is quite a ways back - rear of the baggage door, and forward of the round hatch on the right side. It is of course directly aft of the exhaust. The left side is clean as is the area on the right side forward of this picture.
 
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DesertNomad said:
I noticed this on the belly today... could well have been there since I bought the plane two years ago. What is the best way to treat this... or should I do anything at all? I assume it is filiform corrosion but I guess it could be just a paint bubble.

The plane was in central Texas and now it is in Nevada... very low humidity here.

As you can see, it is not much bigger than a rivet head.

IMG_2881.jpg
Click to expand...
The picture you show is typical of filiform corrosion, that is what we see on small aircraft in our GA fleet.
What you show is very typical of what happens when the strippers and other chemicals get driven into the seams of the fuselage during a re-paint. now they creep out under the new layer of paint, and cause what you are seeing, this is the environment that the microbes love, it is their excrements that cause the acid that etches the aluminum.
First. Do not scrape the paint away, (Like has been suggested), use a small dab of epoxy stripper and remove about a dime sized area of paint. wash clean, wipe dry, that will allow you to see how deep the corrosion is.
Using a stainless steel platers brush remove the black corrosion products by a circular scrubbing motion and clean with a product called alum-prep sold at AS&S. continue that cycle until all black deposits are removed.
then wet with Aldine 1201 (from spruce also). then rinse and dry.
Once clean, and alodined, touch up with any paint you like.

Remember -- there is a very thin coating of pure aluminum over the base metal, you go scraping with any thing that is hard enough to remove paint and you will remove the aluminum layer and make your corrosion problem worse.

when you see his starting on your aircraft, it will soon get worse, keep a close eye on it. don't allow this to get ahead of of you.

When I see this on an annual inspection I get worried about how much corrosion is in the seam from which this spread.

Your clean metal should look like this, the lower left corner of the picture, next to the access panel.
 

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My metal looking into the tail is mostly coated with a coffee colored Corrosion X or some such coating. It was definitely there at the last annual but was not mentioned. It was painted in 2010 by Lancaster Aero in Pennsylvania.

"Soon get worse..."

How soon is soon? I am taking it up to Oregon for a new engine monitor in the next month as my shop here is no longer doing work for non-medical aircraft.

All the rivets on the seem seem ok, but there is that white line of residue... not sure if that came from the seam, the exhaust (that I was cleaning) or both. How would you tell how much corrosion could be in the seam?
 
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DesertNomad said:
My metal looking into the tail is mostly coated with a coffee colored Corrosion X or some such coating. It was definitely there at the last annual but was not mentioned. It was painted in 2010 by Lancaster Aero in Pennsylvania.

"Soon get worse..."

How soon is soon? I am taking it up to Oregon for a new engine monitor in the next month. My shop here is no longer doing work for non-medical aircraft. All the rivets on the seem seem ok, but there is that white line of residue... not sure if that came from the seam, the exhaust (that I was cleaning) or both.
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Every one of the four Cherokee derivatives I've owned had a couple spots of corrosion just like your picture. Always adjacent to a lap seam.
There was never any evidence that the lap seam had been compromised. My mechanic made the repairs pretty well as Tom described. It's one of those things you just need to stay on top of, but the plane isn't suddenly going to have dozens of these popping up like measles - especially if it's hangared or in the dry climate where you are. If you can't get it done before the plane goes to Oregon then have someone repair it properly up there.
 
The correct answer: If that's the only corrosion you have, sigh in relief. You can go another 50 years without any problems.
 
Worried about corrosion now, I gave it a really good looking over and in the empennage, looking from the door by the battery, I do have a few white streaks. These look more like liquid that flowed down and dried. Would corrosion "flow" like this?

Most everything has the sticky brown CorrosionX coating. Any idea what these vertical white streaks are? Could they be from when it was painted with a white base coat that seeped in through the lap joint? It has a white base coat but right outside that seem, it is red (thought the white would have sealed it I guess).

My pre-buy guy (an AP/IA) was asked specifically to look for corrosion and gave it a good report. Several mechanics from my shop have also seen it with no reports of any issues here.

DSCN2569.jpg
 
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GlennAB1 said:
Corrosion byproducts can flow with water, so can oxidized paint. Is there water back there after it rains?
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I don't know. It has only been rained on twice in the two years I have had it. According to previous owners, it has been hangared since at least 1990.
 
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Tom-D said:
First. Do not scrape the paint away, (Like has been suggested),...

Using a stainless steel platers brush remove the black corrosion products by a circular scrubbing motion...

Remember -- there is a very thin coating of pure aluminum over the base metal, you go scraping with any thing that is hard enough to remove paint and you will remove the aluminum layer and make your corrosion problem worse.
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Plastic or phenolic scrapers are recommended when working with aluminum, even clad aluminum.

Stainless steel is bad advice. Refer to table 6-1 in 43.13-1B if you don't believe me
 
DesertNomad said:
I don't know. It has only been rained on twice in the two years I have had it. According to previous owners, it has been hangared since at least 1990.
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GlennAB1 said:
Corrosion byproducts can flow with water, so can oxidized paint. Is there water back there after it rains?
Click to expand...

Rivet is on the bottom ? let's think about that? where is the corrosion by-products going to run to ??

ah DUH
 
GlennAB1 said:
Plastic or phenolic scrapers are recommended when working with aluminum, even clad aluminum.

Stainless steel is bad advice. Refer to table 6-1 in 43.13-1B if you don't believe me
Click to expand...
Do you really still believe that applies to an aircraft that is supported by its own manuals?
Or is it that you do not believe we have learned anything in the last 40 years since that AC was written.?

When you state that, you prove you do not know what an etch is for.
 
Folks ,,,

the part Glen forgets to read.
1. PURPOSE. This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and alteration on non-pressurized areas of civil aircraft of 12,500 lbs gross weight or less. This AC is for use by mechanics, repair stations, and other certificated entities. This data generally pertains to minor alterations; however, the alteration data herein may be used as approved data for major alterations when the AC chapter, page, and paragraph are listed in block 8 of FAA Form 337 when the user has determined that it is:

  1. Appropriate to the product being altered,

  2. Directly applicable to the alteration being made, and

  3. Not contrary to manufacturer’s data.
OBTW here is the rest of it

3. REFERENCE. Title 14 of the Code of Federal Regulations (14 CFR) part 43, § 43.13(a) states that each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance must use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, or practices acceptable to the Administrator, except as noted in § 43.16. FAA inspectors are prepared to answer questions that may arise in this regard. Persons engaged in the inspection and alteration of civil aircraft should be familiar with 14 CFR part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alterations, and part 65, subparts A, D, and E of Certification: Airmen Other than Flight Crewmembers, and applicable airworthiness requirements under which the aircraft was type-certificated.

 
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Tom-D said:
Do you really still believe that applies to an aircraft that is supported by its own manuals?
Or is it that you do not believe we have learned anything in the last 40 years since that AC was written.?

When you state that, you prove you do not know what an etch is for.
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Tom... you helped a friend of mine with his problem with your knowledgeable and well thought out method to repair his issue with his aircraft.

That makes me want to like you.

Your decorum around here makes me want to dislike you.

You know Glenn is going to have a problem with anything you say. Just ignore him. Let people sort out for themselves who they want to take advice from. Stop getting defensive. We all see the ****ing match that evolves for no reason.
 
Tom-D said:
Rivet is on the bottom ? let's think about that? where is the corrosion by-products going to run to ??

ah DUH
Click to expand...

The picture at the top of this thread is on the bottom - the white streaks are on the side. Totally unrelated - just worried about the whole situation.
 
GlennAB1 said:
Stainless steel is bad advice. Refer to table 6-1 in 43.13-1B if you don't believe me
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TABLE 6-1. TYPICAL OXYGEN DURATION TABLE

page53image17848

ACTUAL DURATION IN HOURS AT VARIOUS ALTITUDES

Number of Persons

8000 Ft.

10,000 Ft.

12,000 Ft.

15,000 Ft.

20,000 Ft.

Pilot only

7.6 hr

7.1 hr

6.7 hr

6.35 hr

5.83 hr

Pilot and 1 Passenger

5.07 hr

4.74 hr

4.47 hr

4.24 hr

3.88 hr

Pilot and 2 Passengers

3.8 hr

3.55 hr

3.36 hr

3.18 hr

2.92 hr

Pilot and 3 Passengers

3.04 hr

2.84 hr

2.68 hr

2.54 hr

2.34 hr

Pilot and 4 Passengers

2.53 hr

2.37 hr

2.24 hr

2.12 hr

1.94 hr

NOTE: The above duration time is based on a fully charged 48 cubic-foot cylinder. For duration using 63 cubic-foot cylinder, multiply any duration by 1.3.
 
DesertNomad said:
The picture at the top of this thread is on the bottom - the white streaks are on the side. Totally unrelated - just worried about the whole situation.
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If you clean and treat as I said, you have no worries until it is time to do it again some where else. That is all you can do between total re-paint.
many of the aircraft I see the owner simply scratch it open, and leave it. What's causing the corrosion is then washed away and the process stops.
 
Properly cleaned and treated filiform corrosion, I took the pictures tonight.
 

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Tom-D said:
Do you really still believe that applies to an aircraft that is supported by its own manuals?
Or is it that you do not believe we have learned anything in the last 40 years since that AC was written.?

When you state that, you prove you do not know what an etch is for.
Click to expand...
Wrong again on two accounts.
AC 43.13-1B date issued Sept., 8, 1998
And
The AC also contains "etch" data along with the data confirming the stainless steel should not be used to abrade aluminum.
 
Tom-D said:
If you clean and treat as I said, you have no worries until it is time to do it again some where else. That is all you can do between total re-paint.
many of the aircraft I see the owner simply scratch it open, and leave it. What's causing the corrosion is then washed away and the process stops.
Click to expand...

Thanks. I have asked my shop up in Oregon about it - they'll see my email tomorrow and hopefully it won't be an issue. I understand these are 40-year-old planes. I looked for a Dakota that had spent it's life in Arizona, but I had to settle for Texas (between Austin and Dallas) and Maryland. The tanks were out in 2011 and the rear wing attach points were checked at pre-buy. All ok there.

The white streaks were never commented on - just that no corrosion was found during pre-buy. It's my first plane so I am still learning.
 
GlennAB1 said:
Wrong again on two accounts.
AC 43.13-1B date issued Sept., 8, 1998
And
The AC also contains "etch" data along with the data confirming the stainless steel should not be used to abrade aluminum.
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Here is the 1b table

AC 43.13-1B

9/8/98

TABLE 6-1. Abrasives for corrosion removal.

Its all about abrasives,

there is your confusion factor.

You don't what a platers brush is or what it does.
 
Nite nite Glen, go figure out how a brush can be an abrasive.
 
Tom-D said:
Here is the 1b table

AC 43.13-1B

9/8/98

TABLE 6-1. Abrasives for corrosion removal.

Its all about abrasives,

there is your confusion factor.

You don't what a platers brush is or what it does.
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Tom-D said:
Nite nite Glen, go figure out how a brush can be an abrasive.
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Come back when you understand that abrasives abrade and a metal brush is an abrasive when it removes material.

We purchase wire brushes from Grainger, maybe you should correct them...

Abrasive Wire Brushes:

https://www.grainger.com/category/ecatalog/N-1z0dyod
 
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GlennAB1 said:
Stainless steel is bad advice. Refer to table 6-1 in 43.13-1B if you don't believe me
Click to expand...

Tom-D said:
TABLE 6-1. TYPICAL OXYGEN DURATION TABLE

page53image17848

ACTUAL DURATION IN HOURS AT VARIOUS ALTITUDES

Number of Persons

8000 Ft.

10,000 Ft.

12,000 Ft.

15,000 Ft.

20,000 Ft.

Pilot only

7.6 hr

7.1 hr

6.7 hr

6.35 hr

5.83 hr

Pilot and 1 Passenger

5.07 hr

4.74 hr

4.47 hr

4.24 hr

3.88 hr

Pilot and 2 Passengers

3.8 hr

3.55 hr

3.36 hr

3.18 hr

2.92 hr

Pilot and 3 Passengers

3.04 hr

2.84 hr

2.68 hr

2.54 hr

2.34 hr

Pilot and 4 Passengers

2.53 hr

2.37 hr

2.24 hr

2.12 hr

1.94 hr

NOTE: The above duration time is based on a fully charged 48 cubic-foot cylinder. For duration using 63 cubic-foot cylinder, multiply any duration by 1.3.
Click to expand...
Sadly, I think we can all tell you were oxygen deprived. That's from AC 43.13-2B
 
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Hey, while we have you two here, what's the best way to field dress a prop? Sandpaper? Nail file? Ball peen hammer? Recycled blasting media?
 
GeorgeC said:
Hey, while we have you two here, what's the best way to field dress a prop? Sandpaper? Nail file? Ball peen hammer? Recycled blasting media?
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Typically, you want to do this sort of thing somewhere where there ain't no FAA minions around. So, what I usually do (when necessary) is go land on a gravel bar somewhere and use a rock for the repair followed by some Bondo / rattle can paint to cover it up.

Works every time.
 
Question from a lurker: what is used to remove the corrosion and repaint the area? Is it something special for airplanes or can you just go to Home Depot or AutoZone?
 
jakem said:
Question from a lurker: what is used to remove the corrosion and repaint the area? Is it something special for airplanes or can you just go to Home Depot or AutoZone?
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If it was my airplane, scotchbright and a rattlecan. It ain't like it's the effing the space shuttle.

But I ain't no A&P so I don't know the secret handshake and can't write the magic paperwork.
 
That's it, owners can do whatever they want and A&P/IA's assume responsibility for it at next inspection, unless it's documented.

P.S. Scotchbright is an excellent choice.
 
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