47-42-17\tDOUGLAS: (Was Service Note 3 of AD-781-1.) Applies to the Following DC-6 Aircraft Serial Numbers: Douglas 43061; AAL 42854 to 42865, Inclusive; 42879 to 42880, Inclusive; 42882 to 42896, Inclusive; and 43035 to 43044, Inclusive; UAL 42866 to 42875, Inclusive; and 43000 to 43024, Inclusive; Panagra 42876 to 42878, Inclusive; National 43055 to 43058, Inclusive; Sabena 43062 to 43064, Inclusive; Braniff 43105, 43106; KLM 43111 to 43112, Inclusive; and AAF 42881. \n\n\tInspection required at each 300 hours (or at each 150 hours for non-air-carrier operations).\n \n\tInspect the center spar web between Stations 167 and 184 for cracks in the web along the lower row of rivets which attach the spar web to the leg of the upper spar cap. For aircraft with the 10-tank fuel system this inspection can be properly made only by removing the fuel tank inspection opening near the affected area, since the spar web attaches to the forward side of the spar cap leg and small cracks in the web cannot be detected without close examination. If cracks are found during this inspection or, if between the inspections, leaks occur which are caused by cracks in the center spar web between Stations 167 and 184, the spar web must be reinforced by installing a doubler in accordance with Douglas Drawing 5356664.\n\n\tWhen the spar web reinforcement has been incorporated the special inspection required by this Note may be eliminated. All DC-6 aircraft not mentioned above will be reinforced at the factory.\n \n\t(Douglas Service Bulletin DC-6 No. 29, "Rework Center Spar Web, Stations 167-184, Integral Wing Fuel Tank DC-6 Airplane", covers the same reinforcement as described on Drawing 5356664.)