FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesHard
A technician inspecting a composite control surface with a honeycomb core suspects internal delamination or moisture intrusion but has no access to ultrasonic equipment. Which simple nondestructive method can help detect these defects?
- AEddy current inspection
- BMagnetic particle inspection
- CCoin tap test
- DDye penetrant inspection
Show answer & explanationAnswer & explanation
Correct answer: C. Coin tap test
The coin tap test involves tapping the composite surface with a coin or small hammer and listening for a change in sound; a dull or 'dead' sound compared to surrounding areas indicates possible delamination, disbonding, or moisture intrusion beneath the surface skin.
Why the other options are wrong
- A. Eddy current inspection works on conductive metals, not composite honeycomb structures.
- B. Magnetic particle inspection only works on ferromagnetic materials, not composites.
- D. Dye penetrant inspection detects surface-breaking flaws, not subsurface delamination.
Coin Tap Test
A simple nondestructive inspection method for composite honeycomb structures where tapping the surface and listening for a change in sound reveals internal delamination or disbonding.
- A 'dead' or dull sound indicates a possible disbond
- Requires no special equipment, just a coin or small hammer
- Not effective for locating small or deep defects; supplemented by ultrasonic inspection
Memory trick: 'Tap it and listen — a dull thud means trouble'