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Saturday, February 27 2016 18:03

Aging Gracefully: Addressing Corrosion

Written by  Scott Sherer
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The first place that corrosion was found was on the vertical stabilizer between the stabilizer and the rudder. The first place that corrosion was found was on the vertical stabilizer between the stabilizer and the rudder.

September 2015

In the March 2015 issue of Piper Flyer is a column authored by my hero Lyn Freeman about getting older. Of course I can’t speak for Lyn; only he can. And if he says he’s getting older, than he must be getting older.

As for myself, I’ve been flying 47 years and am on airplane number seven. I’m pretty sure that I’m not getting any older—but I know my airplane is.

As many of you know, I have been writing articles about the restoration of my Seneca II. Most of the major restoration was done over the course of the last decade and I’ve been getting the airplane ready to be painted for the last couple of years. That’s pretty much all that’s left to do before the restoration is complete… and then I’ll have to start over again!

 

Three projects at once
A year ago when it froze over in Wisconsin I couldn’t get my hangar door open for two months. The following summer I conspired with my A&P to do all of my work in January and February when I could keep my airplane in their heated hangar for two months.

Unfortunately this results in losing one month on my annual every year—the 13th month is free if your A&P signs off on your annual inspection on the first of a month—but the trade-off for being able to access my plane over the winter months is well worth it to me.

Last winter I was able to do three projects at once. First, I replaced my center stack of avionics, which I’ve written about in this magazine. (See “In with the New: An Avidyne IFD540 Plug-and-Play Conversion” in the June and July 2015 issues, “A New/Used Autopilot” in the April 2015 issue, and stay tuned for future articles. —Ed.)

Second, I was able to complete the installation of auxiliary fuel tanks that I bought used about five years ago and never installed. (Be on the lookout for this story in a future issue of Piper Flyer, too. —Ed.)

Third, I had my annual inspection about two months early. I hadn’t intended on doing my inspection two months early, but my lead mechanic Erich—whose advice and judgment I covet every time I am in his presence—recommended that I do so while I was installing my auxiliary fuel tanks.

As he said, “Why take apart and reassemble the airplane twice? Save yourself some money, Scott!”
Point—and advice—taken.

The good news from the annual was that my airplane is mostly in excellent shape. The bad news was that I had two small areas that showed some corrosion that needed to be addressed. Right now.

 

That scary “c” word
Hearing the word “corrosion” from your A&P could be likened to hearing the word “cancer” from your physician; they’re both scary.

With all of the restoration projects over the last 10 years, I consider myself fortunate that corrosion was really the only thing that needed addressing in early 2015. I got the plane in questionable condition in 2004, but it was as close to free as any 3,000-hour twin could be.

At that time I gutted the interior and addressed a little bit of corrosion around and under the windows. I overhauled the engines, so everything firewall-forward and behind was addressed. I replaced all of the glass so that there were no leaks going forward, and the landing gear was overhauled and treated.

Most importantly, my technicians sprayed ACF-50 into the wings to arrest any corrosion that may have been there. While ACF-50 weeped from the wings for several years and was quite annoying, it certainly was the right thing to do. I highly recommend this treatment for any aging airplane.

 

AC 43-4A
My other mechanic, Nathan, showed me a publication on corrosion from the FAA. I promptly went home and downloaded Advisory Circular 43-4A, “Corrosion Control for Aircraft,” from the FAA website.
I wholeheartedly recommend that every airplane owner and pilot read this publication. It’s free, contains a complete description on airframe corrosion, and details the many types that can potentially be found on an airplane.

I was surprised to discover there are seven forms of corrosion that occur on airframes. Seven! As depressing as that sounds, I took comfort in the fact that my airplane only had two small areas containing two forms of corrosion.

Without further ado, here are the seven types:
A. Uniform Etch Corrosion
B. Pitting Corrosion
C. Galvanic Corrosion
D. Concentration Cell Corrosion
E. Intergranular Corrosion
F. Exfoliation Corrosion
G. Filiform Corrosion

Rather than try and quote the FAA publication’s description each type, I recommend you download the document and look on page 14. (See Resources for a link to the PDF through PiperFlyer.org. —Ed.) The descriptions are accompanied by photographs, and the document also includes details on how to remove and repair corrosion.

 

Picture 01

Trouble spot number one
The first place that corrosion was found on my aircraft was on the vertical stabilizer between the stabilizer and the rudder. (See picture 1) Once the rudder was removed, Nathan removed the rudder attach hinges—and lo and behold, underneath the hinges was pitting corrosion. Picture 2 gives you a closeup of one of two of these areas.

Picture 2

Picture 03

 Picture 04

At first glance you see that it is shiny and clean. Well, it is shiny and clean, as Nathan had cleaned it up, but you’ll notice that above the large hole is a round area that looks slightly bumpy and not as shiny as the other cleaned-up area.

I thought that Nathan would just clean this area, too—perhaps treat it with an anti-corrosion treatment, like chromate primer—put the hinge back on, reattach the rudder and move on to the next project. Unfortunately it never seems to work out that way.

Instead, Nathan used a caliper to measure the thickness of the good area versus the area with the pitting corrosion. What he discovered was that more than 10 percent of the thickness of the aluminum plate had been eroded. Nathan explained to me that it was not a safe practice to just treat the area and reassemble it when more than 10 percent of the aluminum was gone.

Of course, I’m thinking dollars and Nathan is thinking safety. I’m also thinking I can impress him with my 47 years of airplane ownership and give him the answer. Feeling quite proud of myself, I said,

“Throw on a doubler!”

Nathan slowly shook his head no. To safely address this corrosion, we had to order a new plate, drill out all of the rivets, prime, paint and install the new plate and only then could we put the rudder back. Well, it’s only money, I thought. I told him to proceed.

Picture 6 is the new rudder vertical spar after replacement. Nice and green and new. And safe! Picture 7 is a closeup of that spar.

 

Trouble spot number two
A couple of days later I was back to see the progress on my plane when I got called over to the cabin area. My mechanic had been searching the entire plane for corrosion and not to be denied, he found some. He had removed the back two seats and the carpeting underneath them to check on the control cables and pulleys.

If you look at picture 3 you’ll see a steel angle bracket riveted to two pieces of aluminum. Even after you ignore the green chromate and the glue (that was holding some insulation and carpet down), it’s obvious that the steel plate has a significant amount of rust. Six inches away is another bracket holding another two pieces of aluminum together and that bracket is very rusted, too.
I figured that Nathan would clean it up with an abrasive cleaning pad, re-chromate it, and move on. Instead, Nathan drilled out the rivets and removed both brackets. You can see what he found on Picture 4.

Picture 05

You’ll see on Picture 5 that underneath the brackets the aluminum had turned to dust. Nathan caught this issue in time to prevent the deterioration from spreading to other areas. All we had to do was to order new brackets and the appropriate aluminum parts. And of course, pay for it. (Oh well, it’s just money! I didn’t want to leave any to my kids anyway!)

As for the interior, apparently a water leak occurred a long time ago. That water had pooled under the rear seat and started the corrosion—which had festered for at least a decade—and was missed by all of my prior mechanics.

 Picture 06

Picture 07

No shortcuts—this is structural
Pictures 8, 9 and 10 show corroded parts after they were removed from the airplane. I urge you to have your mechanic dig very deeply into your plane when he or she is doing the next annual. No shortcuts to save a few bucks. Picture 11 shows the area cleaned up with the old parts removed.
When I next visited the heated hangar, I found two signs on my airplane. One was taped near the front door and the other was by rear door.

Picture 08

Picture 09

Picture 10

I asked my corrosion expert, John, about them. He said, “Scott, the parts removed were structural. If someone gets in the plane while these parts are removed, you could bend the fuselage.”
You can add up 2+2 yourself. The corroded parts were structural. Unfortunately all of this corrosion is costing me a couple of months in the shop and some money. But it could have progressed to something unthinkable that would have cost me and my family much more. I don’t even want to go there.

Picture 11 

Picture 12

Remedies and ruminations
Looking at Picture 12, you can see several things. First, you’ll see that the entire floor was cleaned and coated with two coats of primer. John had removed many more aluminum pieces from the area, inspected, cleaned, primed and reinstalled them.

Second, you can also see the two new aluminum spars and steel brackets are installed.
Third, this photo shows you the floor. I mean, the real floor—the only piece of metal between me and a great view of the ground below. There isn’t a second layer anywhere to be found. (Structural integrity becomes even more incontestable when you think about it in these terms.)

Fourth, there are actually several tiny drain holes in the aluminum skin. Any pooled water in this area should drain out, but obviously it didn’t. Why? The carpet throughout the airplane had been glued down with adhesive.

None of the mechanics assigned to the aircraft in the previous 10 years were able to inspect the area without damaging the carpeting, so they didn’t. My mechanic was troubled by this fact.

As I had personally installed the plane’s Airtex upholstery kit, I began to wonder if I didn’t do it correctly. Airtex offers high quality, custom kits that you can install yourself to save on labor costs, and that’s just what I did. (Longtime Piper Flyer Association supporter SCS Interiors offers pre-cut carpet and vinyl floor kits as well. See Resources for the link. —Ed.)

Unfortunately, my Airtex kit didn’t come with any instructions whatsoever. The company’s customer support is excellent; they will answer any installation question you may have. However, nowhere that I found does it say not to install the carpeting with adhesive.

In my case, it was a matter of “you don’t know what you don’t know”—and I didn’t know to ask! I’ve now done four airplanes with Airtex interiors and had glued all of the carpeting down. So what are other people doing?

I asked my mechanic, and he showed me the interior of a twin turboprop. He recommended that next time I do what the expensive business aircraft do: use a fabric fastener (i.e., Velcro) or snaps. That way a mechanic can remove and reinstall carpeting in just a few moments; any water will find its way to the drain holes, and mechanics (and owners) can check for corrosion themselves at any time. Epiphany! Thanks, John.

I’ve ordered new carpeting from Airtex for the backseat of my airplane and it will be here this week. I should be able to get my plane back together and get back in the air next week.

Next winter when I’ve got nothing to do, I’ll order replacement carpeting for the remainder of the airplane, tear up the old stuff and reinstall with snaps and Velcro.

 

Grateful to have the best
At the end of the day, this was the extent of the corrosion damage on my airplane. With a couple of down months and a few dollars comes peace of mind. I have a safe, reliable airplane that’s aging gracefully and safely.

It pays to have a quality team taking care of your airplane, and I feel like I have the best. I hope you do, too.

If you have questions about your airplane or feel like your mechanic isn’t digging deep enough during inspection, it’s time for the two of you to have a serious talk. You have an expectation of quality and safety in your flying machine, and if you’re concerned about something, don’t ignore it. It’s your life!
Piper Flyer Association member Scott Sherer is a multi-engine and instrument rated private pilot. He’s logged over 2,600 hours and is the owner of a 1977 PA-34-200T based at Burlington Municipal (KBUU) in Burlington, Wis. Sherer anxiously awaits the day when N344TB finally gets new paint. Send questions or comments to This email address is being protected from spambots. You need JavaScript enabled to view it..

Read 529 times Last modified on Tuesday, March 15 2016 22:07

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