DIFICATION . SERVICE BULLETIN AN EXTERNAL DETAILED INSPECTION AND AN EXTERNAL NON DESTRUCTIVE INSPECTION (NDI) FOR CRACKING IN THE FUSELAGE SKIN AT THE CHEM-MILL STEPS AT SPECIFIED LOCATIONS OPTION 1 OR OPTION 2 FOR ALL AIRPLANES MOS 20-OCT-2011 AFL 1500(s) SB 737-53-1310 TABLE 2.1 PERFORM FUSELAGE - SK