63-20-03 DOUGLAS: Amdt. 617 Part 507 Federal Register September 14, 1963. Applies to All DC-6, DC-6A, and DC-6B Aircraft, Except Serial Number 44430 (Fuselage No. 500) and Subsequent. \n\n\tCompliance required as indicated. \n\n\tThere have been several instances of cracks causing failure of the lower center spar caps at Station 121, as well as cracking of the wing skin in the same area. Accordingly, the following shall be accomplished: \n\n\t(a) Within 100 hours' time in service after the effective date of this AD, unless already accomplished within the last 400 hours' time in service, visually or X-ray inspect for cracks in the lower center spar cap and the surrounding wing skin area from the inboard side of Numbers 2 and 3 engine nacelles inboard to Station 114.500 and from the outboard side of Number 2 and 3 engine nacelles outboard to Station 184.000. (For X-ray inspection see X-ray procedures and information as described in Figure 2 in Douglas Alert Service Bulletin No. A-849, Reissue No. 1, dated October 1, 1962.) Pay particular attention to the area around the end attachments through the splice fittings. Reinspect at intervals not to exceed 500 hours' time in service from the last inspection. \n\n\t(b) If cracks are found in the lower spar cap, replace the part or repair it in accordance with a method approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region, before further flight, except for a ferry flight in accordance with CAR 1.76. When the new spar cap is installed, the original splice may be reworked or replaced with a redesigned splice. The rework instructions and redesign data are described in Accomplishment Instructions, Parts II and III, respectively, of Douglas Alert Service Bulletin No. A-849, Reissue No. 1, dated October 1, 1962. Also, the splice may be reworked or replaced with a new splice in accordance with a method approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region. If cracks arefound in the surrounding skin area as set forth in (a), the skins shall be replaced or reworked in accordance with the manufacturer's instructions as authorized in Part I, paragraph (2), of Douglas Alert Service Bulletin No. A-849, Reissue No. 1, dated October 1, 1962, or a method approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region. \n\n\t(c) The repetitive inspection specified in (a) may be temporarily discontinued for a period not to exceed 4,000 hours' time in service on those aircraft on which the temporary rework, described in Accomplishment Instructions, Part II of Douglas Alert Service Bulletin No. A-849, Reissue No. 1, dated October 1, 1962, is accomplished. The 4,000 hour temporary discontinuance period will be computed as starting at the time of the temporary rework accomplishment. If the preventive rework as described in (d) is not accomplished prior to the end of the 4,000 hours' time in service period, the repetitive inspection of (a) must bereinstituted and the first reinspection accomplished prior to the expiration of the 4,000 hour period. \n\n\t(d) The special inspections described in (a), (b), and (c) may be discontinued when a specific area as described in (a) has been reworked with the preventive rework as outlined in Accomplishment Instructions, Part III of Douglas Alert Service Bulletin No. A-849, Reissue No. 1, dated October 1, 1962. \n\n\t(e) Upon request of the operator, an FAA maintenance inspector, subject to prior approval of the Chief, Engineering and Manufacturing Branch, FAA Western Region, may adjust the repetitive inspection intervals specified in this AD to permit compliance at an established inspection period of the operator if the request contains substantiating data to justify the increase for such operator. \n\n\t(Douglas Alert Service Bulletin No. A-849, Reissue No. 1, dated October 1, 1962, covers the same subject.) \n\n\tThis directive effective October 15, 1963. \n\n\tRevised November 21, 1963.