|Keep Corrosion from Killing Your Aircraft|
|Written by Floyd Allen|
|Friday, 16 December 2011 11:11|
Have you ever noticed that it often takes a disaster to draw attention to a situation that we ought to be aware of? A disaster that rocked the aviation world took place in 1988 when an Aloha Airlines Boeing 737 airplane suffered a partial in-flight disintegration when an 18-foot section of the fuselage tore apart in flight. This brought recognition to a condition known as widespread fatigue damage (WFD), an ailment that plagues aging aircraft. And, the culprit involved? Corrosion.
“The FAA got real concerned about the situation,” Parrish Traweek, owner of PC Aircraft in San Manuel, Arizona, shared. “As a result, they instituted the Aging Aircraft Program.”
That was a key to the problem with the Aloha Airlines airplane; it was an aging aircraft. Placed into service in 1969, at the time of the disaster it was nearly 20 years old. The thing is, there are a number of General Aviation aircraft in service today that are 20 years old — and older. As a result, it is important that pilots and owners be aware of both the effects of corrosion and the ways to deal with it.
“There are a tremendous number of corrosion types that we need to be aware of and concerned about,” Boyd Maddox out of Rosharon, Texas, said. Operating B & D Aircraft, which is located in the general Houston area, Maddox has a lot of experience where corrosion is concerned. And, he is right; there are a lot of corrosion types, including, but not necessarily limited to, general surface corrosion (aka uniform etch), pitting corrosion, concentration cell corrosion (aka crevice corrosion, metal to metal, between joints), metal ion concentration cells (from high humidity), oxygen concentration cells (under gaskets, wood, or rubber), active-passive cells (from salt water), filiform corrosion (from high humidity), intergranular corrosion (high-strength alloys are most susceptible, such as 2014 and 7075), exfoliation corrosion (an advanced form of intergranular corrosion), galvanic corrosion (from two dissimilar metals contacting each other, such as steel and aluminum), and fretting corrosion (from two metals rubbing together).
As with most things, corrosion doesn’t just happen. Rather, there are four conditions that
must exist: a metal subject to corrosion (anode), dissimilar metals (cathode), presence of a continuous conductive liquid (electrolyte), and electrical contact between the anode and cathode (i.e. rivets and bolts).
Armed with these facts, we can now take an informed look at the corrosion issue.
“What we must constantly keep in mind,” Traweek explained, “is that we must be aware of the fact that we have corrosion that is external and visible, and then we have corrosion that is internal and, unfortunately, out of sight. We need to, however, be aware of both.”
“Parrish is absolutely right,” Maddox concurred. “And, it is often the unseen corrosion that creates the problems.”
In order to help you evaluate the propensity for your aircraft to be affected by corrosion, the first thing to do is determine where your aircraft has spent most of its life. Areas that are most prone to the creation of corrosion are humid areas, especially those near saltwater. The fact that you and your airplane are currently in a not-so-humid area is not good enough; once corrosion starts, if it is not thwarted, it will continue to eat away at the craft until eventually it will make the airplane no longer airworthy. Corrosion is one of the main reasons an airplane is grounded.
To be on the safe side, let’s proceed under the assumption that your airplane is, in fact, in jeopardy of suffering from corrosion attack. The question now is, “How do I protect my prized possession?”
“Keeping in mind that saltwater plays havoc with aircraft,” Traweek began, “if you are in an area where your airplane is exposed to that particular element, you can start by giving your airplane a weekly freshwater bath.” Though currently located in an arid area near Tucson, Arizona, Traweek had lots of exposure to aircraft and saltwater during his stint with the Navy. “As you are bathing your airplane,” Traweek continued, “two places to be especially aware of are the landing gear wheel well and drain holes. Be sure to keep the former clean and the latter open.”
Traweek went on to add that there are two corrosion culprits that all pilots need to check frequently, regardless of where their airplane is kept: rodent urine and fiberglass insulation. “It is imperative that you pull interior panels and check on both of these,” Traweek advised. “The insulation can absorb moisture, due to humidity, thus creating the propensity for corrosion to occur in some of those out-of-sight areas I was talking about.”
“I think one of the best preventive measures to take,” Maddox interjected, “especially in the unseen areas that Parrish refers to, is to spray the inside of a fuselage and aluminum wings with a good corrosion shield. This is best accomplished on a hot day, as this allows the shield to get between metal surfaces. Spray it with a fine, even mist, ensuring that there is a good, even film. Be aware that the treatment might seep out for the next year or so, making the outside somewhat messy.”
There are two corrosion shields that are generally recognized by the General Aviation community as being effective: ACF-50 and CorrosionX. Both can be applied to the entire airframe, and each protects all areas — seen and unseen. Executives at the firms who manufacture each very graciously shared the advantages of their product. Maintaining a positive position in regard to each, rather than a comparative evaluation, I’m providing the information shared, and I’ll let you determine which might best meet your needs.
“Our product,” Fred Kenner, vice president of sales at Corrosion Technology, which manufactures CorrosionX, began “stops any existing white corrosion for up to two years. In fact, it does such a good job that we are the only company in the U.S. that meets the Navy’s military specification MIL-C-81309E for corrosion prevention (http://www.everyspec.com/MIL-SPECS/MIL+SPECS+(MIL-C)/MIL-C-81309E_18416/).”
That, however, is not its only strengths. Because it is comprised of 7 percent volatile organic compounds (VOCs), CorrosionX can be used in electrical areas, due to its low level of solvent, thus ensuring that it will not attack plastic. Further, it is a wonderful penetrating lubricant.
ACF-50 has been around for some 25 years, and it was first introduced at the International Seaplane Fly-In at Moosehead, Maine. Offered by Lear Chemical in Mississauga, Ontario, Canada, ACF-50 was designed to treat the entire airframe, and not to be used for spot treatment.
“Before I extol our product,” Mark Pearson, the owner and general manager of Lear Chemical, began, “I would like to expand a bit on what Parrish said about those areas that tend to promote corrosion. The most susceptible areas are those in the tropics close to the ocean. As a result, airplanes in Florida and the Caribbean need to be treated, even if they are hangared. Another culprit in creating corrosion is industrial pollutants that result in the creation of acid rain. As a result, we strongly recommend that those pilots whose airplanes are housed in industrial areas also strongly consider having their craft treated, as well.
“I think one of the keys to the success of ACF-50,” Pearson continued, “is the fact that it has active chemistry. As a result, it has the ability to migrate, thus becoming an excellent moisture displacement.”
Pearson went on to explain that ACF-50 works well as a preventive measure, as it provides a totally flexible hydrophobic (water-hating) film. Too, it can also help protect electrical connectors from corrosion.
Both products are applied in a manner that allows the inside, as well as the outside, of the airplane to be treated. Although anyone can apply these products under Part 43 as an owner/operator, it is difficult to get an effective application without the proper equipment. So, it is probably best to have these products applied by technicians at FBOs or tech centers that offer the service.
Up to this point, the focus of discussion has been on corrosion in hidden areas. What about corrosion on exposed areas? In those situations, Boyd Maddox believes that a direct approach is the way to go.
“When you find corrosion in open areas,” he advised, “you need to remove it, and then protect the area from future damage.” Maddox went on to explain that the area should be sanded with good old-fashioned sandpaper. Once that is accomplished, treat the area with a mild solution of phosphoric acid, and then paint on some alodine. The area will turn a golden color, and when it dries, you can wash it off. If you’re dealing with aluminum, you will want to prime the area with a zinc chromate primer, and then paint. If the area you are working with is steel, you will want to use a Rust-Oleum primer and paint.
“Boyd’s suggestion is excellent,” Pearson said, “and reminds me of a point that I think needs to be made. Many aircraft, when they leave the factory, are zinc-chromated, and, as a result, the owners of those airplanes believe they need never do anything else to protect them. Truth is, that’s not necessarily the case.”
What Pearson is alluding to is the fact that, down through the years, the zinc’s sacrificial qualities are expended. As a result, a craft 30 years old or more may very well need to be attended to and receive a protective coating.An owner must protect his craft from corrosion, even though it may not be visible to the naked eye. Corrosion can bring about an early demise to our airplanes. Inasmuch as forewarned is forearmed, I trust you will make arrangements to protect your airplane today!
|Last Updated ( Friday, 16 December 2011 11:16 )|