Your aircraft is a large metal object that can be affected by numerous factors such as rapidly changing temperatures, rain, sleet, hail, salt water, and other related issues. All of these can lead to one major problem for the metal on your aircraft, corrosion.
This article will help you understand what aircraft corrosion actually is, different types of corrosion, and which aircraft are susceptible to corrosion. Then we will offer you some treatment options.
Aircraft corrosion costs the aviation industry millions of dollars during inspections and repair work. Corrosion is responsible for approximately 7% of the airworthiness directives and 20% of service difficulty reports (Swift). If you are an aircraft mechanic or a technician, you have to be vigilant in looking for any signs of corrosion.
Corrosion is the attack on metal by an electrochemical reaction to the surrounding environment.
When there is a period of contact between metal and chemical or electrochemical agents, corrosion can begin to appear. These electrochemical agents are things such as acids, alkalis, and salts. So, inferring from this data, one knows that airplanes near marine climates or near areas that contain high amounts of industrial particles and fumes are going to be in greater danger of corrosion forming.
Although corrosion on aluminum can often appear as a whitish or gray color that looks as if the aluminum has turned to a dull color, it is similar to the reddish colored rust on ferrous metal.
Leaving this corrosion on your aircraft can lead to that aircraft becoming unairworthy in a matter of years.
5 Types of Aircraft Corrosion
Uniform surface attack corrosion is the most common form and is caused by exposed metal to the oxygen in the air. This form is quite simple to understand. For example, if paint is worn off the fuselage, leaving this area exposed, that can accelerate the decay.
Intergranular corrosion is an uncommon type of corrosion but a very nasty form to deal with. Often difficult to find and once found, it is too late to save that piece of metal on your aircraft. With this type of corrosion cracking may occur along grain boundaries. Intergranular literally means “between grains or crystals”.
Stress corrosion appears in parts like engine crankshafts or landing gear. Often stress crack corrosion and intergranular corrosion are both present when the other arises. These fractures have a brittle appearance. These cracks are deemed catastrophic due to the abundance of them and how hard they are too see without a microscope.
Crevice, or deposit corrosion, can occur anywhere that moisture can be found. This form of corrosion is also common anywhere pollutants can be trapped. Key areas to look for this include skin joints or rivets on an oil-stained belly.
Lastly, filiform corrosion can be found on poorly prepared aluminum surfaces. This corrosion appears as worm-like lines underneath the paint and can lead to your paint bubbling and peeling off.
Which Types of Aircraft are at Risk?
Unfortunately, any metal aircraft can be at risk for corrosion. Some aircraft are more likely candidates for corrosion than others. AOPA.org mentions specifically that single-engine Cessna’s built from 1977-1982 are particularly susceptible to filiform corrosion.
Aviation Consumer magazine stated that Cessna switched to a polyurethane paint and did not follow the manufacturer’s recommendations for the surface preparations. Cessna then created a special program to help owners with repainting their aircraft from this specific time frame.
Other aircraft are susceptible as well, specifically those located in coastal areas. Appraisers have been quoted stating that buyers will shy away from purchasing an aircraft that has spent time in Florida, along the Gulf Coast, or in Pacific Coast areas of the west.
Now that you have a good understanding of how corrosion works and where to look for it, the question is: how do you fix it? The key to corrosion is keeping the airframe free of moisture.
We suggest two great products that are widely known for being very effective at fixing and helping to prevent corrosion issues within or on your aircraft.
One great product that can help corrosion issues is ACF-50, Anti-Corrosion Formula. According to their website, “ACF-50 is a state of the art, anti-corrosion/lubricant compound that has been specifically designed for the Aerospace Industry.”
This product can last up to 24 months but may need to be reapplied every 12 months, depending on the climates your aircraft is exposed to.
ACF-50 is an ultra-thin fluid film compound that actively penetrates through corrosion. Once it has penetrated the corrosion, it begins to emulsify and encapsulate the electrolyte, pulling it away from the metal surface.
Another great benefit of ACF-50 is the way in which it continues to “creep” into tight seams, lap joints, micro cracks, and around rivet heads. This will help find corrosion and dissipate it in areas that may remain unseen to mechanics and technicians.
According to their website, CorrosionX Aviation “takes corrosion control to a whole new level.” This product features advances in Polar Bonding and Fluid Thin Film Coating (FTFC) technology. This formula helps displace moisture and stop corrosion.
CorrosionX Aviation’s biggest selling point is how widely used throughout the U.S. military it is. This product is the only product that currently meets the military’s tough, new MIL-PRF-81309F Type II performance requirement.
Military branches such as the U.S. Air Force, U.S. Coast Guard, U.S. Navy and the U.S. Army amongst others all use this product. Other widely known names such as NASA and Boeing are listed as customers as well.
CorrosionX is recommended to be applied every other year. The application process takes less than four hours, so it is well worth your time. The key aspect of this product is the polar bonding. The molecules in CorrosionX and the metal form a magnet-like bond to one another.
Tip: Don’t worry about CorrosionX seeping out of lap seams and around rivets and screws, this is a good thing. Seeing this means that CorrosionX is doing its job of penetrating and pushing moisture and corrosion out of those tiny spaces as well as protecting future corrosion.
Other options include cladding, chemical treatments, and sealants.
Cladding is an effective method that involves coating a sheet with very thin layers of pure aluminum to protect from corrosion. When the cladding is compromised, such as at seams and joints, the sheet material becomes vulnerable to corrosion.
Another option is a chemical treatment such as Alodine. This treatment can enhance the corrosion resistance of the pure aluminum cladding.
Painting your aircraft is the most common form of sealant used for corrosion protection. Polyurethane paints create a thick, impenetrable barrier that can keep moisture away from the metal for 10 years or more. Paint is the most effective way to keep corrosion from forming on your aircraft but it does not protect the inside of the airframe.
As you now know, corrosion is among the top growing issues in the aviation world. Although there has yet to be a perfect remedy for corrosion, there are ways to help slow down the process. Understanding what is happening, where to look, and some products you can use is a great first step to keeping your aircraft airworthy.
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Cessna Single Engine Safety Initiative PDF
Swift, S., “Rusty Diamond”, 24th ICAF Symposium, May 2007.