The engine fan ducts used in the F100 fighter are titanium alloy structures consisting of inner and outer plates (“skins”) and intervening interior “side” walls that connect the two plates and are arranged in a “honeycomb” fashion. The panels are ultrasonically inspected in immersion in pulse-echo or through-transmission modes to look for common defect conditions: interior water in the honeycomb cells, disbonds between the skins and side walls, and tears in the honeycomb side walls. In such C-scan inspections, focussed transducers are used with the beam(s) normal to the inner and outer skins.