Sections of AC 20-37E
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Surface Corrosion. The loss of surface metal due to chemical or electro-chemical action with visible oxidation products usually having a contrasting color and texture to the base metal. Surface corrosion, as shown in Figures 1-1 and 1-2, generally results when the corrosion protection on a metal surface has been removed by erosion or by polishing. Therefore, removing paint and corrosion protection, such as when polishing blades, is not recommended.
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e. Blade Polishing. The FAA receives frequent inquiries from airplane owners and maintenance personnel asking whether it is acceptable to polish propeller blades. It is almost always not acceptable. Corrosion protection such as paint and anodize should not be removed from the surface of a propeller blade. Propeller blades must be maintained to the type design. If the original design had corrosion protection and the instructions for continued airworthiness call for corrosion protection, then the corrosion protection should be maintained to those instructions.
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(8) Do not polish blades unless specifically permitted by the manufacturer?s instructions.
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Corrosion, Surface. Surface loss of metal due to chemical or electro-chemical action. On polished surfaces begins as a dulling of surface, soon becoming frosted, followed by widespread pitting.