FAA Aviation Mechanic Airframe (AMA)Airframe InspectionMedium
During an inspection of a composite wing skin, a technician taps the surface with a coin and hears a dull, flat sound in one area compared to a clear ringing sound elsewhere. What does this indicate?
- AA hairline surface scratch that does not affect structural integrity
- BNormal variation due to differences in panel thickness
- CProper bonding with excess resin content
- DA subsurface delamination or disbond in the composite structure
Show answer & explanationAnswer & explanation
Correct answer: D. A subsurface delamination or disbond in the composite structure
A dull or 'dead' sound during a coin tap test on composite structure indicates a void, delamination, or disbond between layers, since a solidly bonded laminate produces a clear ringing sound. This is a standard NDT method for composite inspection.
Why the other options are wrong
- A. A surface scratch would not change the internal tap-test sound response.
- B. Thickness variation alone does not typically produce a dull sound change.
- C. Excess resin would not cause a change in tap sound in this manner.
Coin Tap Test (Composite NDT)
A simple nondestructive inspection method using a coin or tap hammer to detect delaminations or disbonds in composite structures by listening for changes in sound.
- Clear ringing sound = solid bond
- Dull/flat sound = delamination or void
- Common on composite skins, honeycomb panels, and bonded structures
Memory trick: Dull thud = 'dud' bond underneath