The "tap test", as used on fiberglass homebuilts, is used to detect
voids (air bubbles) in the epoxy/glass matrix. One usually uses a
Quarter to gently tap the surface. If there are any voids, the
difference in sound will be noticeable.

Morgans wrote:
there HAS to be a better way than a tap test.

Stefan wrote:
Actually, no. Like it or not, but there are situations where the human
eye, ear and feel is still the most accurate method, if carefully done
by a skilled person, of course. (This is just a generic remark. I am no
specialist in composites at all and haven't the slightest clue what
problem airbus might or might not have.)