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Interpreting a coin tap test

Aviation Mechanic Airframe (AMA) practice question 9 of 30 on Non-Metallic Structures. ACS element AM.II.B.K18 · 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 a tap test of a honeycomb sandwich panel, a technician hears a dull, thud-like sound. What does this response indicate?

  1. AA well-bonded, solid area of structure
  2. BA change in face sheet resin content only
  3. CA disbond or delamination in that area
Show the answer and explanation

Correct answer: C. A disbond or delamination in that area

  • A — incorrect A clear, sharp, ringing sound is what indicates a well-bonded solid structure, not a dull thud.
  • B — incorrect Resin starvation and resin richness are conditions found by visual inspection; the tap test response is interpreted as bond condition.
  • C — correct A dull or thud-like sound indicates a discrepant area, and tap testing is the most common technique for detecting delamination and disbond.

BACKGROUND

Audible sonic testing, also called coin tap, uses frequencies in the audible range and is a surprisingly accurate method in experienced hands. The inspector taps the area with a solid round disc or lightweight hammer-like device and listens to the response of the structure. A clear, sharp, ringing sound indicates a well-bonded solid structure, while a dull or thud-like sound indicates a discrepant area. The tapping rate must be rapid enough that differences in tone are discernible, and the work should be done in as quiet an area as possible. The method is not reliable for structures with more than four plies and is often used to map damage on thin honeycomb face sheets.

STUDY TIP

Tie the two sounds directly to their meanings, and also remember the limitation that tap testing is unreliable on laminates thicker than four plies.

KEY POINTS

  • A dull, thud-like sound indicates disbond or delamination.
  • A clear, sharp ringing sound indicates sound bonded structure.
  • Tap testing is not reliable beyond four plies.

SOURCES

  • FAA-H-8083-31B ch07 "Audible Sonic Testing (Coin Tapping)"
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MORE ON NON-METALLIC STRUCTURES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.