Black residue around rivet heads

Aviation Mechanic Airframe (AMA) practice question 11 of 20 on Metallic Structures. ACS element AM.II.A.K1 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONDuring an inspection of a riveted joint, a mechanic finds a dark, greasy black residue trailing away from several rivet heads. What does this residue indicate?

ARivets that have loosened in the holes
BCorrosion pitting beneath the rivet head
CRelative movement, called fretting

Show the answer and explanation

Correct answer: C. Relative movement, called fretting

A — incorrect The handbook states specifically that this residue is not an indication of looseness, even though it does show the component is under significant stress.
B — incorrect The residue itself is the product of motion, not of a corrosive attack under the head; pitting or cracking can only be judged after the residue is cleaned off and the surface examined.
C — correct The black residue is aluminum oxide formed by a small amount of relative motion between the rivet and the adjacent surface, a condition called fretting corrosion or smoking.

BACKGROUND

Not every defect in a metal airframe announces itself as a dent or a crack. A working rivet is one that moves under structural stress but has not loosened enough for the movement to be seen, and its only outward sign may be a dark, greasy residue or deteriorated paint around the head. That residue is aluminum oxide dust generated by tiny relative motions between the rivet and the sheet, which the handbook calls fretting corrosion, or smoking, because the dust forms a dirty trail. Finding it means the joint is carrying significant stress, and over time the thinning of the moving pieces can propagate a crack. The residue can be removed with a general purpose abrasive hand pad so the surface underneath can be inspected for pitting or cracking.

STUDY TIP

Learn the outward signs of internal trouble: smoking rivets, canted or wrinkled skin, and parallel diagonal wrinkles across a wing. Each one points to a different kind of hidden damage.

KEY POINTS

A black, smoke-like trail at a rivet head is aluminum oxide from relative motion (fretting), not proof the rivet is loose.
A working rivet moves under stress but the movement itself cannot be seen.
Clean the residue off with an abrasive pad and inspect the surface for pitting or cracking.

SOURCES

sources/ama-airframe/ch04.txt "Inspection of Riveted Joints"

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