64-16-01\tBOEING: Amdt. 760 Part 507 Federal Register July 8, 1964. Applies to Model 720 Series Aircraft. \n\n\tCompliance required as indicated. \n\n\tSeveral failures of bolts attaching the main landing gear centering cylinder and snubber assembly to the inner cylinder assembly and to the truck assembly have occurred. To preclude further failures, the following or an equivalent approved by the Chief, Aircraft Engineering Division, FAA Western Region, shall be accomplished: \n\n\t(a)\tWithin the next 500 hours' time in service after the effective date of this AD, unless already accomplished: \n\n\t\t(1)\tReplace the existing bolts attaching the main landing gear centering cylinder and snubber assembly to the inner cylinder assembly and to the truck assembly with larger diameter bolts specified in step (e) and in accordance with the provisions of the note following step (e) of paragraph 3, Modification Data of Boeing Service Bulletin No. 1570. The provisions of Boeing Service Bulletin No. 1570A shall also be accomplished; or \n\n\t\t(2)\tAs an alternative, remove the existing 9/16 inch-diameter bolts, P/N's 63-9663 and 66-26031, and replace with 9/16 inch-diameter Standard Press Steel (SPS), P/N's 63425-9-24 and 63425-9-28 (H.T. 220,000 p.s.i. MIN.) respectively. The new bolts are to be reworked in accordance with the instructions on Figure 1 of Boeing Service Bulletin No. 1570, or later approved revisions to Boeing Service Bulletin No. 1570. \n\n\t(b)\tWithin the next 3,000 hours' time in service after the effective date of this AD, accomplish the following, unless already accomplished: \n\n\t\t(1)\tRemove existing bolts, P/N's 63-9663 and 66-26031, or P/N's 63425-9-24 and 63425-9-28. \n\n\t\t(2)\tRework terminal and inner cylinder lug per Figures 3 and 5 and steps 3b and 3c of Boeing Service Bulletins Nos. 1570 and 1570A respectively. \n\n\t\t(3)\tRework truck assembly lug per Figure 4 and step 3d of Boeing Service Bulletins Nos. 1570 and 1570A. \n\n\t\t(4)\tReinstall centering cylinder and snubber assembly using bolts 66-15739-1 and 66-15739-2 as shown in Figure 2 of Boeing Service Bulletin No. 1570. \n\n\t(c)\tThe modifications in (a)(1) or (a)(2) need not be accomplished if the provisions of (b) are accomplished prior to the next 500 hours' time in service following the effective date of this AD. \n\n\t(d)\tCompliance with paragraph (b) may be extended to the next main landing gear overhaul or to 6,000 hours' time in service after the effective date of this AD, whichever occurs first, if the following is accomplished: \n\n\t\t(1)\tOperators who have complied with (a)(1) shall replace the bushings prior to 3,000 hours' time in service after the bushing has been reworked.\n \n\t\t(2)\tOperators who have complied with (a)(2) shall replace the bolts at periods not to exceed 2,000 hours' time in service until (b) is accomplished. \n\n\t(Boeing Service Bulletins Nos. 1570 and 1570A cover this same subject.) \n\n\tThis directive effective August 7, 1964.