90-21-10 BOEING: Amendment 39-6761. Docket No. 90-NM-47-AD. \n\n\tApplicability: Model 727-100 and -100C series airplanes, listed in Boeing Service Bulletin 727-53-0109, Revision 3, dated September 28, 1989, certified in any category. \n\n\tCompliance: Required as indicated, unless previously accomplished. \n\n\tTo detect delamination, cracking, and/or corrosion of fuselage crown skin circumferential joint at body station (BS) 1080 and to prevent depressurization, accomplish the following: \n\n\tA.\tFor airplanes modified in accordance with Part IV of Boeing Service Bulletin 727-53-0109, Revision 3, dated September 28, 1989: Within the next 15 months after the effective date of this AD, accomplish an internal close visual inspection in accordance with the NOTE in Part I.A of the service bulletin. \n\n\t\t1.\tIf no corrosion is detected, repeat the inspection at intervals not to exceed 30 months. \n\n\t\t2.\tIf corrosion is detected, prior to further flight, repair in accordance with PartIII of the service bulletin. \n\n\tB.\tFor airplanes not modified in accordance with Part IV of Boeing Service Bulletin 727-53-0109, Revision 3, dated September 28, 1989, within the next 15 months after the effective date of this AD, accomplish an external visual inspection in accordance with Part II.A of the service bulletin and a LFEC inspection in accordance with Part II.B of the service bulletin. Perform an internal close visual inspection within 15 months after the external inspection, in accordance with Part II.C of the service bulletin. \n\n\t\t1.\tIf no corrosion is detected, repeat the external visual inspection at intervals not to exceed 15 months and, the LFEC inspection and internal close visual inspection at intervals not to exceed 30 months. \n\n\t\t2.\tIf corrosion is detected, prior to further flight, accomplish one of the following: \n\n\t\t\ta.\tRepair in accordance with Part III of the service bulletin; or \n\n\t\t\tb.\tConduct a low frequency eddy current (LFEC) inspection in accordance with Part II.B of the service bulletin. \n\n\t\t\t\t(1)\tIf corrosion depth is found to be less than 10 percent of the skin thickness, conduct a high frequency eddy current (HFEC) inspection in accordance with Part II.D of the service bulletin. \n\n\t\t\t\t\t(a)\tIf no cracking is detected repeat the HFEC and LFEC inspections at intervals not to exceed 15 months. \n\n\t\t\t\t\t(b)\tIf cracking is detected, repair prior to further flight, in accordance with Part III of the service bulletin. \n\n\t\t\t\t(2)\tIf corrosion depth is found to be greater than 10 percent of the skin thickness, repair prior to further flight, in accordance with Part III of the service bulletin. \n\n\tC.\tWithin the next 3,000 landings or 30 months after the effective date of this AD, whichever occurs first, accomplish a HFEC inspection in accordance with Part II.D of Boeing Service Bulletin 727-53-0109, Revision 3, dated September 28, 1989. \n\n\t\t1.\tIf no cracking is detected, repeat the inspection at intervals not to exceed 4,000 landings or 48 months, whichever occurs first. \n\n\t\t2.\tIf cracking is detected, prior to further flight, repair in accordance with Part III, or IV of the service bulletin. \n\n\tD.\tModification in accordance with Part III of Boeing Service Bulletin 727-53-0109, Revision 3, dated September 28, 1989, constitutes terminating action for the inspections required by this AD for those modified areas. \n\n\tE.\tModification in accordance with Part IV or Part V of Boeing Service Bulletin 727-53-0109, Revision 3, dated September 28, 1989, terminates the inspections required by paragraph C. of this AD for those modified areas. \n\n\tF.\tModification in accordance with Part III of Boeing Service Bulletin 727-53-0109, Revision 1, dated January 11, 1973, or Revision 2, dated June 20, 1973, constitutes terminating action for the inspections required by paragraph C. of this AD, for those modified areas. Within the next 15 months after the effective date of this AD, accomplish a close external visualinspection for cracking of the skin adjacent to the fastener heads in the modified areas. If cracks are detected, repair in accordance with Part III or IV of the service bulletin. If no cracks are detected repeat the close external visual inspection at intervals not to exceed 15 months. \n\n\tG.\tAn alternate means of compliance or adjustment of the compliance time, which provides an acceptable level of 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\tH.\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. \n\n\tThis amendment (39-6761, AD 90-21-10) becomes effective on November 13, 1990.