44-20-02 BOEING: (Was Service Note 1 of AD 719-1 and Service Note 1 of AD-726-1.) Applies to 307 Series Aircraft. \n\tInspect by visual means all square aluminum alloy 24SRT tubing for cracks in the following locations: wing spars, front spar fuselage bulkhead, rear spar fuselage bulkhead, and fin and stabilizer attachment bulkheads. These inspections shall be conducted at intervals specified and in the following manner: \n\tA.\tSA-307B. In the inspection of 24SRT members in this model airplane, it is recommended that the visual inspection procedure outlined for Boeing Model 314 and A-314 under AD 45-04-01 be followed. If defects are located, they shall be reported to the FAA for evaluation. Past experience has shown that once cracking starts, it may progress at a rapid rate, thus requiring closer inspections and corrective action. It shall also be the operator's responsibility to keep a record of all cracks on this model airplane. This record shall be revised periodically to showthe status of existing cracks and to record newly developed cracks. Copies of the original report and all revised pages should be submitted to the FAA for examination. \n\t\t1.\tINSPECTIONS OF READILY ACCESSIBLE AREAS. These inspections shall be conducted at intervals not to exceed 150 hours of operation or 90 days, whichever occurs first. This inspection is intended to cover only those portions of 24SRT tubing that are accessible to visual inspection through available inspection panels, removal of gap strips and the openings in the nacelles. \n\t\t2.\tDETAILED INSPECTIONS. These inspections will be conducted annually or at engine overhaul periods, whichever occurs first. This inspection is required of all 24SRT tubing visible through all available inspection panels, removal of gap strips, leading edges, wing tips, stress plates and fuel tanks. The use of at least a 10-power glass will be required. To more thoroughly cover the wing area, it will be necessary for a man to crawl outboardin the wings as far as possible. \n\t\t3.\tX-RAY INSPECTION. This type of inspection is required annually. Inspect by x- ray all inaccessible portions of the 24SRT spar chord members for their entire length. This inspection may coincide with annual inspection noted under 2. \n\tB.\tSA-307B-1. At intervals not to exceed 850 hours of operation or 120 days, whichever occurs first. If defects are located, they shall be repaired in a manner satisfactory to the FAA. \n\tC.\tS-307. At intervals not to exceed 700 hours of operation or 120 days, whichever occurs first. If defects are located, they shall be repaired in a manner satisfactory to the FAA.