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material thickness to make it unairworthy. An ounce of prevention and all that.
Treating corrosion can be a tricky task and shouldn’t be taken lightly. You can easily turn a “quick fix” into a major repair. If you grew up helping your grandparents work on tractors, your first instinct might be to grab a wire brush and rattle-can primer from the National Aviation Parts Association – or, as non-aviation types like to call it, NAPA – and get to work. But that’s not the best way to go about it. You can perform some corrosion repairs your- self, but unless you have technical guidance from either AC 43-4B or your airplane’s structural repair manual, and experience performing such repairs, you’re probably better off leaving it up to your mechanic or repair shop. If you’re cleaning your airplane and see a spot that gets your attention, clean it and get some photos, preferably with a ruler beside the damage – again, us maintenance folks love pictures with rulers – and get in touch with your favorite mechanic or shop. Many manufacturers have a structures department that will help you and your mechanic assess the damage and formulate a plan to take care of it if there’s any uncertainty about its severity.
If you decide to take care of a few spots yourself, make sure you know what kind of material you’re dealing with. If you’re working on a piece of sheet aluminum, there’s a good chance that it’s a sandwiched, corrosion-resistant
material called Alclad. Alclad is an aluminum alloy with very thin sheets – about 5 percent of the total thickness – of pure aluminum on the outer surfaces. If you’re using Scotchbrite or sandpaper to remove corrosion, it won’t take more than a couple of swipes to dig down through that protective surface sheet and into the unprotected alloy, which is far more susceptible to corrosion.
It isn’t always easy to identify what kind of metal you’re working on, either. Unless you can see the interior portion of the sheet you’re working on – and if it’s not primed and still has the identifying markings visible – I’d leave it up to the pros. You don’t want a little surface corrosion to turn into a skin repair.
Corrosion is one of the biggest challenges to keeping an airplane airworthy. Gone undetected, it can reduce an airplane to a pile of dust. The good news is that with proper care and a little bit of attention, corrosion can be, at most, an occasional inconvenience instead of a major show-stopper.
1st Source
http://1stsource.com
Elliott Cox is a pilot and the Director of Maintenance for a Part 91 Corporate Flight Department in the Southeast. You can reach him at his website TheWritingFlyer.com or by email at elliott@thewritingflyer.com.
October 2022 / TWIN & TURBINE • 11