90-21-15 BOEING: Amendment 39-6767. Docket No. 90-NM-75-AD. \n\n\tApplicability: Model 737 series airplanes, listed in Boeing Alert Service Bulletin 737- 55A1031, Revision 2, dated November 30, 1989, certificated in any category. \n\n\tCompliance: Required as indicated, unless previously accomplished. \n\n\tTo detect cracking in the horizontal stabilizer center section rear spar upper chord, accomplish the following: \n\n\tA.\tPrior to the accumulation of 35,000 landings, or within 350 landings after October 18, 1982 (the effective date of AD 82-21-02, Amendment 39-4473), whichever occurs later, unless accomplished within the last 4,150 landings, and thereafter at intervals not to exceed 4,500 landings since the last inspection, eddy current or dye penetrant inspect the upper surface of the forward flange of the horizontal stabilizer center section rear spar upper chord for cracks in the area of each beam gusset plate in accordance with "Part A-Inspection" of Boeing Alert Service Bulletin 737-55A1031, Revision 2, dated November 30, 1989, or previous FAA- approved revisions. If cracks are found, repair, modify, or replace the damaged chord before further flight, in accordance with Boeing Model 737 Structural Repair Manual, Subject 51-30-09, or Boeing Alert Service Bulletin 737-55A1031, Revision 2, dated November 30, 1989, or previous FAA-approved revisions. \n\n\tB.\tAfter repair, modification, or replacement, resume the repetitive inspections required by paragraph A. of this AD, at the following schedule or within the next 1,000 landings, whichever occurs later: \n\n\t\t1.\tPrior to the accumulation of 9,000 landings after repair.\n \n\t\t2.\tPrior to the accumulation of 35,000 landings after modification. \n\n\t\t3.\tPrior to the accumulation of 50,000 landings after replacement. \n\n\tThereafter, repeat the inspections at intervals not to exceed 4,500 landings. \n\n\tC.\tAn alternate means of compliance or adjustment of the compliance time, which provides an acceptable levelof safety, may be used when approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \n\n\tNOTE: The request should be submitted directly to the Manager, Seattle ACO, and a copy sent to the cognizant FAA Principal Inspector (PI). The PI will then forward comments or concurrence to the Seattle ACO. \n\n\tD.\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD. \n\n\tAll persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue S.W., Renton, Washington 98055-4056. \n\n\tAirworthiness Directive 90-21-15 supersedes AD 82-21-02, Amendment 39-4473.This amendment (39-6767, AD 90-21-15) becomes effective on November 16, 1990.