An aircraft and most of its structures and components are made of metal, which is inherently prone to corrosion. Corrosion presents continuous safety risks to aircraft and aircraft components and annually costs millions of dollars in aircraft inspections and repair work. If left untreated, corrosion can cause deterioration in the thickness of the aircraft’s materials that can lead to a loss of structural integrity and eventually to catastrophic failure.
The document FAA Advisory Circular 43-4B contains a summary of the currently available data regarding the identification and treatment of corrosive attacks on aircraft structures, aircraft components, and engine materials.
Aircraft manufacturers continually design aircraft to prevent corrosion through the careful selection of structural materials, plating, paints, sealants, and other corrosion-inhibiting coatings used on the parts of the aircraft most prone to corrosion, as well as the addition of water drainage systems. Aircraft designs typically allow easy access to the aircraft structures for frequent maintenance and corrosion inspections.
There are two general classifications of the causes of corrosion, direct contact with a corrosive chemical or by an electrochemical reaction with corrosive agents, either in its environment or where two dissimilar metals meet.
In both types of corrosion, the metal is converted into a metallic compound after contact with various acids, alkalis, or salts. The corrosion typically appears as a discoloration on the surface of the metal due to chemical deposits, or as a small depression in the metal.
The major contributing factors to the development of aircraft corrosion are hostile environmental factors and climatic conditions. Water vapor, either alone or in combination with salts found in marine and coastal climates, is a powerful source of corrosion. Aircraft operated in areas that contain pollutant particles or other airborne industrial contaminations also heighten the risk of corrosion.
Usually, the development of corrosion will depend on how old the aircraft is, what type of environment it is based in, how it is stored, and how often it is cleaned.
Preventing corrosion is much easier than treating it and keeping an aircraft free of moisture is usually the most effective means of preventing corrosion.
One of the main ways to protect the aircraft is by storing it in a hangar. If access to a hangar is not possible, various aircraft covers could be used to keep the majority of the aircraft dry.
Removing salt and other corrosive agents by cleaning the exposed areas of the aircraft will reduce corrosion formation. The routine use of protectants and lubricants applied to the aircraft help seal the metal against moisture. Any chipped or flaking paint should be properly addressed and re-painted.
Proper inspections and preventative maintenance are required to keep the aircraft metal from corroding and prevent more costly and extensive aircraft dismantling and repair actions. Following a corrosion control program with periodic inspections of the primary aircraft structures can lead to the early detection of corrosion to keep the corrosion to a predictable, manageable level.
When inspecting aircraft, the parts of the aircraft that harbor moisture or are constantly exposed to outside debris are especially prone to corrosion and need to be monitored. They include the battery compartments, wheel wells and landing gear, cooling air vents and water entrapment areas.
When evidence of corrosion is found it is critical that the extent and nature of the corrosion be established to determine the proper removal process. Light surface corrosion can usually be removed with gentle abrasion, depending on the type of metal. A corrosion inhibitor and new primer and paint can then be added to protect the area from further deterioration. If the corrosion is severe and has removed a substantial amount of metal, replacement of the part is usually the only solution.