What was found
INVESTIGATED REPORTS OF IN-FLIGHT POPPING NOISES FROM UNDER FLOOR AREA ADJACENT TO CABIN DOOR. FOUND FORWARD LT AUXILLARY TANK STRUCTURE UNDERSIDE HONEYCOMB PANELS DISBONDED FROM TANK STRUCTURE SHEETMETAL. NO CORROSION NOTED, HONEYCOMB MATERIAL APPEARS TO HAVE SEPARATED FROM SHEETMETAL AT ADHESIVE BOND LINE. SLIGHT DEFORMATION OF CURVED UNDERSIDE OF FUEL TANK STRUCTURE NOTED. INFORMATION FORWARDED TO MFG FOR FOLLOW-UP INVESTIGATION. POSSIBLE CAUSE IS VACUUM IN FUEL TANK DUE TO VENTING PROBLEM CAUSING TANK DEFORMATION AND/OR HONEYCOMB ADHESIVE FAILURE. (K)