What does a black 'smoky' residue from rivets on an aircraft typically indicate?

A black 'smoky' residue from rivets on an aircraft typically indicates fretting corrosion. This type of corrosion occurs when two surfaces are in close contact and experience slight relative motion, which can lead to wear and the creation of debris. The black residue is often a result of metal particles that have oxidized due to the mechanical action, and this is particularly evident around rivets where there may be vibration or other forces at play.

Fretting corrosion is notably problematic in aviation, as it can compromise the integrity of the riveted connections, leading to potential structural issues if not addressed. Recognizing this residue allows for timely maintenance and inspections to ensure the safety and longevity of an aircraft's components. Understanding this corrosion mechanism is crucial for anyone involved in the maintenance and inspection of aircraft structures.