Final answer:
Fretting corrosion on aircraft is likely at areas with surface contact and relative motion, such as fastened joints. Protective coatings can be compromised by vibration, leading to oxidation and rust with potential for sudden failure.
Step-by-step explanation:
Fretting corrosion is most likely to occur on parts of an aircraft where there is contact and relative motion between surfaces. This type of corrosion can be induced by vibration and repetitive small-scale movement that causes the protective coating, such as paint, to wear away, exposing the underlying metal. Areas particularly susceptible include locations where parts are fastened together, such as bolted joints or areas where control surfaces meet the airframe. Lead (Pb)/iron (Fe) junctions in an aircraft should be closely monitored since Pb serves as the cathode, leading to increased oxidation of the more active Fe.
As an example, if the protective paint on an iron or steel surface of an aircraft is scratched, exposing the metal, this area can become anodic. Meanwhile, the larger areas remain cathodic due to greater oxygen exposure, and as the Fe begins to oxidize, rust formation occurs. Such corrosion could eventually lead to structural failure with little visible indication of degradation. Hence, regular inspections of an aircraft's surfaces and joints are critical for maintaining structural integrity.