FAA Aviation Mechanic Airframe (AMA)Airframe StructuresHard
During a borescope inspection, a technician finds a composite honeycomb sandwich panel that sounds dull and 'dead' in one area when tap tested, compared to a sharp, clear ring elsewhere on the panel. What does this finding most likely indicate?
- ADisbond or delamination between the skin and honeycomb core
- BA change in paint finish causing sound absorption
- CNormal variation in panel thickness
- DProper bonding with excess adhesive fillet
Show answer & explanationAnswer & explanation
Correct answer: A. Disbond or delamination between the skin and honeycomb core
A dull, dead sound during a tap (coin-tap) test indicates a disbond or delamination between the face skin and the honeycomb core, since the skin is no longer well-bonded and cannot transmit vibration properly. A sharp, clear ring indicates good bonding, while paint or thickness variation would not typically produce this distinct dull sound pattern.
Why the other options are wrong
- B. Paint finish differences do not meaningfully affect the tap test's acoustic response for detecting disbonds.
- C. Thickness variation alone would not typically produce a dull, dead sound in a properly bonded structure.
- D. Excess adhesive fillet is unrelated to acoustic tap test response and does not cause a dull sound.
Coin-Tap Test (Tap Test)
A simple nondestructive inspection method using a coin or tap hammer to detect disbonds/delaminations in composite honeycomb structures by listening for changes in sound.
- Sharp, clear ring indicates good bond
- Dull, dead sound indicates disbond or delamination
- Common for quick field checks of sandwich composite structures
Memory trick: 'Dull thud means the sandwich has gone bad (disbonded).'