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

A black 'smoky' residue near rivets on an aircraft is typically indicative of fretting corrosion. This type of corrosion occurs when two metal surfaces rub against each other, which can happen if there is movement or vibration in the structure. The abrasion leads to tiny particles of metal being worn away, creating a black, powdery residue that is often mistaken for grease or dirt.

Fretting corrosion is concerning in aviation, as it can compromise the integrity of the metal, weakening the structural components over time. It often manifests around rivets due to the localized stress and movement at these points, where two metal components are joined. Identifying this black residue is crucial for maintenance and inspection, as it serves as a warning sign to check for underlying structural issues related to the rivets and the materials involved.

Understanding this can guide maintenance technicians to take preventive measures and address any issues before they lead to significant damage or failure in aircraft operations.