75-24-04 BOEING: Amendment 39-2425. Applies to all 707 and 720 series airplanes certificated in all categories which (1) were delivered after January 28, 1966, including Serial Numbers 18955 and 18979, with more than 12,000 hours time in service on the horizontal stabilizer center section rear spar upper chord assembly or (2) were modified by Boeing Service Bulletin No. 2243, Revisions 1 through 7, with more than 12,000 hours time in service since modified or (3) had the bushings removed for lug bore inspection and corrosion removal, with 12,000 hours or more time in service since the last flanged bushings were installed. Compliance required as indicated. \n\tA.\tWithin 100 hours time in service after the effective date of this AD, unless inspected within the last 125 hours time in service, and every 225 hours thereafter, visually inspect the horizontal stabilizer center section upper rear spar for cracks in the outer surface of the right and left hand terminal lugs. The cracks initiate in the bushed holes at the terminal fittings. \n\t\tIf cracks are found, replace the horizontal stabilizer center section rear spar upper chord assembly or repair prior to further flight in accordance with B or C below. \n\tB.\tInstall a strap in accordance with Boeing Drawing No. 65C15785. This strap must be replaced in accordance with Boeing Drawing No. 65C15785 after 3,000 hours time in service. \n\tC.\tModify in accordance with Boeing Service Bulletin No. 3243 or in a manner approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region. Such modification constitutes terminating action for this airworthiness directive.\n \tThe manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). \n\tAll persons affected by this directive, who have not already received these documents from the manufacturer, may obtain copies upon request to Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124. The documents may also be examined at FAA Northwest Region, 9010 East Marginal Way South, Seattle, Washington. \n\n\tThis amendment becomes effective November 24, 1975.