This is one of a series of Handbooks prepared for the purpose of assisting personnel engaged in the maintenance and repair of aircraft. This publication explains in detail methods used for the prevention and combatting of corrosion. Various forms of corrosion are described so that untrained personnel can differentiate between inconsequential and serious corrosion so as to determine whether parts should be replaced or repaired. When corrosion occurs in aircraft structures, the resulting damage may be serious and must be given immediate attention. Because serious corrosion results in loss of strength and ductility in the thin, highly-stressed metals used in aircraft construction, every effort must be made to protect the surfaces under all conditions. The commonly used aircraft metals (aluminum, steel, and magnesium) are resistant to corrosion after treatment applied to them by the manufacturer. However, they will corrode seriously under certain conditions if not given preventive maintenance. When applying corrosion preventive measures to a part, first refer to section IV to obtain the protective requirements for the type of part and second to section VI for detailed instruction for the application of protective coatings. Section III describes the cleaning of aircraft and the treatment for corroded parts.