91-06-06 BOEING: Amendment 39-6921. Docket No. 90-NM-176-AD. \n\n\tApplicability: Model 727 series airplanes, listed in Boeing Service Bulletin 727-53-0072, Revision 5, dated June 1, 1989, certificated in any category. \n\n\tCompliance: Required as indicated, unless previously accomplished. \n\n\tTo prevent rapid decompression of the airplane, accomplish the following: \n\n\tA.\tWithin the next 2,500 landings or 1 year after August 21, 1989 (the effective date of Amendment 39-6262, AD 89-15-06), whichever occurs first, or prior to the accumulation of 28,000 landings, whichever occurs later, unless previously accomplished within the last 2,000 landings or 2 years; and thereafter at intervals not to exceed 4,500 landings or 3 years, whichever occurs sooner; perform a high frequency eddy current (HFEC) inspection for cracks of the skin at fuselage lap joints S-4 and S-10 where the upper skin is less than 0.056 inch thick, from body station (BS) 259 to BS 1183, in accordance with Paragraph A. of Part I of the Accomplishment Instructions of Boeing Service Bulletin 727-53-0072, Revision 5, dated June 1, 1989 (hereinafter referred to as "the service bulletin"). If any cracks are detected, prior to further flight, repair in accordance with Part III of the Accomplishment Instructions of the service bulletin. \n\n\tB.\tWithin the next 2,500 landings or 18 months after February 12, 1990 (the effective date of Amendment 39-6461, AD 90-02-10), whichever occurs first, or prior to the accumulation of 28,000 landings, whichever occurs later, unless previously accomplished within the last 18 months; and thereafter at intervals not to exceed 4,500 landings or 3 years, whichever occurs sooner; perform a high frequency eddy current (HFEC) inspection for cracks of the fuselage skin at lap joints, S-14, S-19, S-20, and S-26 at locations where the upper skin is less than 0.056 inch thick from body station (BS) 259 to BS 1183, in accordance with Paragraph A. of Part I of the AccomplishmentInstructions of the service bulletin. Inspection is not required adjacent to protruding head fasteners located under fairings. If any cracks are detected, repair prior to further flight, in accordance with Part III of the Accomplishment Instructions of the service bulletin. \n\n\tC.\t1.\tWithin the next 6 months after August 21, 1989, unless accomplished within the last 9 months, or prior to the accumulation of 28,000 landings, whichever occurs later; and thereafter at intervals not to exceed 15 months; perform a detailed external visual inspection for cracks and for corrosion of fuselage lap joints (including S-4 and S-10) between BS 259 and BS 1183, except for S-14 (between BS 360 and BS 1183) on those airplanes identified in the service bulletin as Group I airplanes, in accordance with Paragraphs B.1. and B.2. in Part I of the Accomplishment Instructions of the service bulletin. Adequate lighting must be used for this inspection and, if necessary, inspection aids such as a mirror and 10X glass. Inspect for small cracks, bulging skin between fasteners, blistered paint, dished or popped rivet heads, loose fasteners, and delamination. Repair cracks, corrosion, and delamination in accordance with paragraph D. of this AD. \n\n\t\t2.\tThe repetitive inspection required by paragraph C.1. of this AD, may be conducted at intervals not to exceed 30 months in lieu of the 15 month interval for lap splices that have protruding head fasteners and are located under airplane fairings. Fasteners under the edge of the fairing also may be visually inspected at 30-month intervals, provided there is no evidence of cracking or corrosion of the lap joint from the edge of the fairing forward two frame stations for the leading edge of the fairing and aft two frame stations for the trailing edge of the fairing. \n\n\tD.\t1.\tIf cracks, delamination, or corrosion are detected at lap splices, prior to further flight, perform a HFEC inspection for cracks in the affected lap joint along the complete panel length in accordance with paragraph A. or B. of this AD, except for areas under fairings as described in paragraph C.2. of this AD. Repair cracks prior to further flight, in accordance with Part III of the service bulletin. If corrosion or delamination is found at any lap joint, repeat the HFEC inspection at intervals not to exceed 15 months or 3,000 landings, whichever occurs first; or repair the delamination prior to further flight, in accordance with Part II of the Accomplishment Instructions of the service bulletin. Repair the corrosion in accordance with paragraph D.2. of this AD. Where a panel is interrupted by a major cutout, such as an entry door or cargo door, the panel is considered to end at the cutout. \n\n\t\t2.\tIf corrosion or delamination is found, prior to further flight, conduct a low frequency eddy current (LFEC) inspection, in accordance with Part II of the Accomplishment Instructions of the service bulletin, of the lap joint along the complete panel length, except for areas under fairings as described in paragraph C.2. of this AD, to determine corrosion depth. If corrosion does not exceed 10 percent of the skin thickness, repeat the LFEC inspection at intervals not to exceed 2,000 landings or 6 months, whichever occurs first, until repaired in accordance with Part II, Paragraph B.2., of the Accomplishment Instructions of the service bulletin. If corrosion exceeds 10 percent of skin thickness, prior to further flight, repair in accordance with Part II, Paragraph C.1. of the Accomplishment Instructions of the service bulletin. \n\n\tE.\tTo conduct the inspections required by this AD: \n\n\t\t1.\tRemove the paint, using an approved chemical stripper; or \n\n\t\t2.\tEnsure that the fastener head is clearly visible. \n\n\tF.\tModify fuselage skin lap joints where the upper skin is less than 0.056 inch thick by replacing the upper row of fasteners with protruding head fasteners, in accordance with Part IV of the Accomplishment Instructions of the service bulletin, in accordance with the following schedule: \n\n\n\nNumber of Landings on \n\tAugust 21, 1989 \n\t(the Effective Date of\nAmendment 39-6262) \nModify Within the Next\n45,000 or more\n4 years after August 21, 1989 \n\nLess than 45,000 \n6 years after August 21, 1989, or prior to the accumulation of 28,000 landings, whichever occurs later \n\n\t\t\n\t\t1.\tBefore oversizing holes, perform a HFEC inspection of the hole to ensure it is crack- free. If cracking is detected, prior to further flight, repair in accordance with the service bulletin. \n\n\t\t2.\tIf the hole was not HFEC inspected prior to fastener installation, the skin must be visually inspected in accordance with paragraph C.1. of this AD within 1 year after August 21, 1989, or 4 years after the fastener installation, whichever occurs later, and reinspected thereafter at intervals not to exceed 15 months.\n \n\t\t3.\tReplacement with protruding head fasteners constitutes terminating action for the repetitive HFEC inspections required by paragraph A. or B. of this AD. The inspections required by paragraph C. of this AD are to continue. \n\n\tG.\tModification in accordance with Figure 4 of the service bulletin constitutes terminating action for the inspections required by paragraphs A., B., and C. of this AD for the modified area. \n\n\tH.\tBlind fasteners installed in the lap joints are to be used as an interim repair only. The blind fasteners specified in the service bulletin have a life of 10,000 landings and all other blind fasteners have a life of 3,000 landings before they must be replaced with protruding head solid fasteners. The blind fasteners must be inspected for loose or missing fasteners after accumulating 3,000 landings since installation or 1,000 landings after the effective date of the AD, whichever occurs later, and thereafter at intervals not to exceed 2,500 landings. Blind fasteners installed prior to August 21, 1989, must be replaced prior to the threshold specified in this paragraph orwithin 3,000 landings after August 21, 1989, whichever occurs later. \n\n\tI.\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\tJ.\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 SW., Renton, Washington. \n\n\tAirworthiness Directive 91-06-06 supersedes AD 89-15-06, Amendment 39-6262, and AD 90-02-10, Amendment 39-6461. \n\n\tThis amendment (39-6921, AD 91-06-06) becomes effective on April 8, 1991.