85-01-07 BOEING: Amendment 39-4983. Applies to Model 737 series airplanes certificated in all categories listed in Boeing Service Bulletin 737-57-1087, Revision 4, dated November 18, 1983. Unless previously accomplished, prior to the accumulation of 10,000 landings or within 180 days or 2500 flight cycles after the effective date of this AD, whichever occurs later, accomplish the following to detect cracking which may lead to failure of the body buttock line (BBL) 70.85 rib upper chord: \n\n\tA.\tVisually inspect the BBL 70.85 rib upper chord for cracks in accordance with Table I of the Flight Safety Addendum of Boeing Service Bulletin 737-57-1087, Revision 4, or later FAA approved revisions. Repeat the inspections at intervals not to exceed 5000 landings. \n\n\tB.\tVisually inspect the BBL 70.85 rib upper chord repair angles installed in accordance with Boeing Service Bulletin 737-57-1087, Revision 2, or earlier FAA approved revisions, for cracks in accordance with Table I of the Flight Safety Addendum of Boeing Service Bulletin 737- 57-1087, Revision 4 or later FAA approved revisions. Repeat the inspection at intervals not to exceed 5000 landings. \n\n\tC.\tIf cracks are detected, prior to further flight replace or repair cracked parts in accordance with Table I of the "Accomplishment Instructions" in Boeing Service Bulletin 737- 57-1087, Revision 4, or later FAA approved revisions; and continue the repetitive inspections of paragraph A., above, at intervals not to exceed 5000 landings. \n\n\tD.\tParts repaired in accordance with the "stop drilling" interim action (a) in Table I of the "Accomplishment Instructions" of Boeing Service Bulletin 737-57-1087, Revision 4, must be reinspected at intervals not to exceed 1500 landings and must be repaired in accordance with Part III or IV of Boeing Service Bulletin 737-57-1087, Revision 4, or later FAA approved revisions, within two years of the accomplishment of the interim repair. \n\n\tE.\tThe requirements of this AD areterminated if the Preventative Modification Part III or the Special Modification Part IV of the Accomplishment Instructions in Boeing Service Bulletin 737-57-1087, Revision 3, or later FAA approved revisions, is incorporated. \n\n\tF.\tAirplanes may be ferried to a maintenance base for repairs or replacement of parts in accordance with FAR 21.197 and 21.199 with prior approval of the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region. \n\n\tG.\tFor the purpose of this AD, and when approved by an FAA Maintenance Inspector, the number of landings may be computed by dividing each airplane's time in service by the operator's fleet average time from takeoff to landing for the aircraft type. \n\n\tH.\tAlternate means of compliance which provide an equivalent level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region, Seattle, Washington. \n\n\tI.\tUpon request of the operator, an FAA Maintenance Inspector, subject to prior approval of the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region, may adjust the repetitive inspection intervals specified in this AD to permit compliance at an established inspection period of an operator, if the request contains substantiating data to justify the adjustment period. \n\n\tAll persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to the Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124. These documents may also be examined at FAA, Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington. \n\n\tThis amendment becomes effective February 25, 1985.