64-10-02\tBOEING: Amdt. 726 Part 507 Federal Register May 6, 1964. Applies to Models 707 and 720 Series Aircraft Serial Numbers 17586 through 17612, 17614 through 17652, 17658 through 17690, 17692 through 17724, 17903 through 17906, 17918 through 17930, 18012 through 18037, 18054 through 18063, 18067 through 18071, 18083 through 18087, 18165 through 18167, 18245 through 18251, 18334 through 18339, 18351 through 18357, 18372 through 18375, 18378, 18381 through 18395, 18411, 18414 through 18422, 18424, 18425, 18451 through 18452.\n \n\tCompliance required as indicated unless already accomplished. \n\n\tTo provide improved airplane controllability in case of horizontal stabilizer electrical trim malfunction, and to provide a switch with sufficient operating torque to assure switch operation necessary for horizontal stabilizer electrical trim operation in both directions, accomplish the following: \n\n\t(a)\tWithin 3,000 hours' time in service after the effective date of this AD on all theabove listed airplanes, except Serial Numbers 18393 through 18395, 18451, and 18452, remove the existing stabilizer limit switches (Boeing P/N 66-11056 or Control Company of America P/N 1HS6) and associated mounting brackets and install new limit switches Control Company of America P/N H10-1001 and associated mounting brackets and cams. This installation shall be accomplished in accordance with Boeing Service Bulletin No. 1635(R-1), Paragraph 3, Part I, or an FAA approved equivalent. \n\n\t(b)\tWithin 1,000 hours' time in service after the effective date of this AD on airplane Serial Numbers 18393 through 18395, 18451 and 18452, replace the four horizontal stabilizer electrical trim limit switches Control Company of America P/N H10-59 with Control Company of America P/N H10-1001 switches in accordance with Boeing Service Bulletin No. 1635 (R-1), Paragraph 3, Part II, or an FAA approved equivalent. \n\n\t(Boeing Service Bulletin No. 1635(R-1) covers this same subject.) \n\n\tThis directiveeffective June 5, 1964.