60-02-04\tBOEING: Amdt. 86 Part 507 Federal Register January 21, 1960. Applies to the following Model 707 Series aircraft only: Serial Numbers 17586 through 17591, 17609 through 17612, 17628 through 17652, 17658 through 17672, 17691, 17696 through 17702, 17925 through 17927. \n\n\tTo increase the capabilities and reliability of the Mach trim warning lights and the Mach warning and fire warning bell systems the following modification(s) shall be accomplished as indicated: \n\n\tUnless already completed, the following shall be accomplished by April 30, 1960. \n\n\t(a)\tRemove Mach and fire warning bell support bracket, Boeing P/N 69-1640, from below flight engineer's table and rework to accept redesigned warning bell assembly Boeing P/N 69-50013 or equivalent. Install reworked bracket and redesigned components as shown in Boeing Drawing 65-2801. (Boeing Service Bulletin No. 444 pertains to this same subject.) \n\n\t(b)\tInstall two diodes, Boeing assembly 69-43070-6, in the Mach trim systemresistor box and revise the indicating light circuitry such that this light will indicate when the system is not turned on as well as indicating Mach trim system malfunctions. (Boeing Service Bulletin No. 474 (R-1) describes a satisfactory modification.)