Nothing creates fear in the hearts of mechanics, manufactures, owners, and operators alike than the words “aircraft corrosion.” For the mechanic, aircraft corrosion means careful and lengthy inspections in damp, dark, and hard-to-get-to places, usually followed by detailed and often major repairs. To the owner and operator corrosion is just plain bad news, and will mean their aircraft will be out of service for expensive repairs. In some cases it will also mean an unfortunate and considerable loss of asset value. For regulatory agencies, corrosion can be considered a life-threatening event that must be aggressively addressed and prevented.
How can we, those who make our livelihood maintaining aircraft, prevent, control, detect, and repair corrosion? This has been our challenge since we began using metal on our airplanes. I would be willing to place a bet that the Wright Flyer, and the aluminum engine block in particular, picked up some corrosion while going through its paces at Kitty Hawk. Charles Edward Taylor probably made some preventative modifications on the next models to prevent corrosion from further hindering the progress being made in aircraft development.
We all know that metals exposed to damp environments over time, particularly salty marine environments, will inevitably experience damage. For those of us who have been out of the chemistry class for a couple of years, corrosion is the electrochemical deterioration of metal that is a result of its chemical interaction with the surrounding environment. Natural science ruled our industry as much in 1903 at Kill Devil Hill, as it does in our 2009 operating environments. When there is a corrodible metal or alloy, the presence of a dissimilar conductive material (cathode), electrolytes, and an electrical path between the anode and the cathode, we will have corrosion on our airplanes.
As aircraft maintainers we understand that corrosion prevention is an ongoing task that is never completed. We understand better than anyone else that maintaining an aggressive control program that includes inspection, prevention treatments, and repairs is vital to ensuring the airworthiness of our aircraft.
Watch out for corrosion!
Corrosion is insidious and can develop anywhere at any time. From experience on the flight line, overhaul docks, and various back shops, I suggest that there are several key areas that must be visually inspected, as well as have nondestructive tests routinely performed. I would like to share my own priority list of places that aircraft corrosion will most likely occur. They are in the following order of probability.
- Floor boards and structure around and under lavatories and galleys — should be clear why this is top of the list
- Seat tracks and any place on the flight deck or main cabin that passengers and crew can spill drinks or drop food
- All battery compartments
- All sumps and drains, specifically in integral type fuel tanks; metal-eating microbes grow in water trapped in fuel tanks — I have made mortgage payments, paid for vacations and school tuition with overtime wages I earned from major structural repairs caused by corrosion in fuel tanks, lavs, and galleys
- Structures below baggage compartment floors, particularly the lower stingers and clips, bottom skin lap joints, and areas under antennas, pitots, and drain mast
- All wheel wells and flap gaps — landing gear and wheel assemblies and flap drives, flap tracks, and exposed rods and cables are very susceptible to corrosion, especially if the aircraft is flying in marine environments or airports with winter deicing operations
- Electrical compartments, including cannon plugs and attachment points
- Avionic component connector pin and circuit board edge connectors
- Hydraulic compartment structure
- Aircraft cables
- Engine exhaust and oil sump and drain areas