90-09-09 BOEING: Amendment 39-6586. Docket No. 89-NM-217-AD. \n\n\tApplicability: Model 747 series airplanes, listed in Boeing Service Bulletin 747-53- 2064, Revision 4, dated September 23, 1983, certificated in any category. \n\n\tCompliance: Required as indicated, unless previously accomplished. \n\n\tTo detect cracks in the front spar pressure bulkhead chord, accomplish the following: \n\n\tA.\tFor airplanes that have not been modified in accordance with Boeing Service Bulletin 747-53-2064, dated July 25, 1972: Within the next 1,000 landings after October 15, 1984 (the effective date of AD 84-18-06, Amendment 39-4912), or prior to the accumulation of 10,000 landings, whichever occurs later, and thereafter at intervals not to exceed 7,000 landings, conduct a high frequency eddy current (HFEC) inspection of the chord to detect cracks between stringers S-37 and S-39 at the chord radius, heel, and flanges adjacent to the fastener holes identified for inspection in Boeing Service Bulletin 747-53-2064, Revision 4, dated September 23, 1983. If cracks are found in the pressure bulkhead chord, accomplish the repair in accordance with the service bulletin before further flight. Repair of cracks along the chord radius under 5 inches in length, or across a chord flange that have not severed the chord flange, may be deferred 1,000 landings by stop drilling and reinspecting for crack progression every 200 landings using HFEC. If crack progression is found, repair in accordance with the service bulletin prior to further flight. Inspections are to continue at intervals not to exceed 7,000 landings after repair. \n\n\tB.\tFor airplanes that have been modified in accordance with Boeing Service Bulletin 747-53-2064, dated July 25, 1972: Within the next 1,000 landings after October 15, 1984 (the effective date of AD 84-18-06, Amendment 39-4912), or prior to the accumulation of 10,000 landings after the modification, whichever is later, and thereafter at intervals not to exceed 10,000 landings, conduct an HFEC inspection to detect cracks in the front spar pressure bulkhead lower chord heel from stringers S-37 to S-39, and conduct an ultrasonic inspection to detect cracks in the fuselage skin originating at the indicated fastener holes beneath the forward drag splice fitting flanges, in accordance with the service bulletin. If any cracks are found, repair in accordance with Boeing Service Bulletin 747-53-2064, Revision 4, dated September 23, 1983, before further flight. Inspections are to continue at intervals not to exceed 10,000 landings after repair. \n\n\tC.\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, FAA, Northwest Mountain Region. \n\n\tNOTE: The request should be forwarded through an FAA Principal Maintenance Inspector (PMI), who will either concur or comment, and then send it to the Manager, Seattle Aircraft Certification Office. \n\n\tD.\tFor the purposes of complying with this AD, subject to acceptance by the assigned FAA Maintenance Inspector, the number of landings may be determined by dividing each airplane's number of hours time in service by the operator's fleet average time from takeoff to landing for the airplane type. \n\n\tE.\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 Airplanes, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 17900 Pacific Highway South, Seattle, Washington, or Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington. \n\n\tThis amendment supersedes Amendment 39-4912, AD 84-18-06. \n\tThis amendment (39-6586, AD 90-09-09) becomes effective on June 4, 1990.