What was found
WHILE COMPLYING WITH SB 187, ANTENNA INSPECTION AND MODIFICATION PART 1, THE LT FS 223.98 UPPER FUSELAGE FRAME CHANNEL RETURN FLANGE AT THE LT NR 1 LONGERON INTERSECTION WAS FOUND CRACKED. THE DAMAGED FRAME SECTION IS COMMON TO THE NR 1 LONGERON AND IS SHIMMED AND ATTACHED AT THAT POINT BY ONE AN4704 RIVET. THE UPPER FLANGE ON THE FRAME HAD COMPLETELY BROKEN AWAY. IN ADDITION, THE NR 1 LONGERON HAD CRACKED ALONG THE LOWER BEND DIAGONALLY 2 INCHES FORE AND AFT OF THE ATTACHMENT POINT TO THE FRAME AT FU. ST 223.98. WITH AN ANTENNA BEING MOUNTED TO FUSELAGE IN THAT AREA APPARENTLY IT WAS APPLYING STRESS ON THE STRUCTURE. COMPLETION OF SB MOD PROVIDED THE ADDITIONAL SUPPORT FOR ANTENNA INSTALLATION.