83-21-02 R1 BOEING: Amendment 39-4745 as amended by Amendment 39-5215. Applies to those Model 747 series airplanes certificated in all categories listed in Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision. To prevent failure of the trailing edge flap tracks, accomplish the following: \n\n\tA.\tInspect the external surface of the trailing edge flap tracks visually for cracks or corrosion penetration within the threshold landings set forth in Table I after the effective date of this AD, and thereafter at the repetitive intervals not to exceed those shown in Table I, below, in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision. These external visual inspections are to continue until the modifications of paragraph D are accomplished. \n\n\t\t\t\t\tTABLE I \n\n\nEFFECTIVITY AIRPLANE LINE NO.\t\t \nTHRESHOLD FOR \nINITIAL\t\tINSPECTIONS \n\nREPETITIVE INSPECTION INTERVALS \n\n\nDuring the initial 250 landings after effective date of the AD. \nDuring the 251 thru \n500 landings after \nthe effective date \nof the AD. \n001-400\t\n(Group I)\t\t\n50 Landings \n50 Landings \n30 Landings \n401-584\t\n(Group II)\t\t\n100 Landings \n100 Landings \n100 Landings \n\n\tB.\tIf any cracks are found in any flap track, replace the cracked track before further flight. This replacement criterion applies to all future inspections required by this AD. \n\n\tC.\tIf any corrosion pits, which have completely penetrated the track web, are visible on the outside of any track web, perform a repeat visual external inspection for cracks in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision, at intervals not exceeding 30 landings. Replace the track within 200 landings after discovery of the corrosion pits, or before further flight if a crack is found. These replacement criteria apply to all future inspections required by this AD. \n\n\tD.\tIf there are not visible track webcracks and no corrosion pits through either web, modify by drilling the 5/8-inch diameter drain holes in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision, within 500 landings or six months after the effective date of this AD, whichever occurs first. Flush the track cavity per instructions in the Service Bulletin. \n\n\tNOTE: Airplane Flap Tracks previously modified by a single 3/8-inch diameter drain hole must still be modified in accordance with the requirements of this paragraph. \n\n\tE.\tConcurrent with the modifications of paragraph D., above, perform an internal borescope inspection of the flaptrack in accordance with procedures defined in Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA-approved revision, to determine if corrosion exists. If corrosion or pitting is found, determine its extent by accomplishing the track web X-ray inspection specified in the service bulletin. \n\n\t\t1.\tPerform repeat externalinspections for cracks or corrosion penetration through track webs at the intervals shown in the following Table II: \n\n\t\t\t\t\tTABLE II \n\n\nMaximum Flap Setting Used for landings\nInternal\t\tCorrosion\tClassification (b)\nMaximum External \nInspection Intervals (Landings) Visual Inspection \nMagnetic Particle or Penetrant Inspection \n\n25 degrees(a)\t\t\nHeavy\n200\t\n250 \n\nModerate\n400\n450 \n\nLight\t\t\t\n800\t\n850 \n30 degrees\t\t\nHeavy\t\t\t\n50\n65 \n\nModerate\t\t\n100\t\n115\n\nLight\n250\t\n265 \n\n\t\t\t(a)\tQuadrant and alternate extension system must be modified to block off selection of flaps 30 degrees.\n \n\t\t\t(b)\tClassification terms are defined in Paragraph G. of the Accomplishment Instructions of the referenced service bulletin. \n\n\tF.\tRepeat the X-ray inspection specified in paragraph E., above, in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA-approved revision, on tracks indicating medium or light internal web corrosion at intervals not exceeding one year or until heavy web corrosion is indicated, whichever occurs first. This twelve month inspection interval may be extended to fifteen months, provided a monthly repeat visual inspection is initiated at the twelfth month and continued until the X-ray inspection is accomplished. When the classification of the internal corrosion changes then the inspection interval changes as indicated in paragraph E.1., above. If the previous two X-ray inspections show that corrosion progression has been arrested, the X-ray reinspection interval may be increased from 12 to 24 months until subsequent X-ray inspections indicate noticeable corrosion progression. At that time, the interval for X-ray inspection shall revert to 12 months. \n\n\tG.\tApply organic corrosion inhibitor (BMS 3-23 or equivalent) to the aft cavity of each flap track after the borescope inspection of paragraph E. and at intervals not exceeding 6 months in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1,or later FAA approved revision. \n\n\tH.\tFor purposes of complying with this AD, subject to acceptance by the assigned FAA Principal Maintenance Inspector, the number of landings may be determined by dividing each airplane's hours time in service by the operator's fleet average from takeoff to landing for the airplane type. \n\n\tI.\tUpon request of the operator, a FAA Principal Maintenance Inspector, subject to prior approval by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region, may adjust the inspection interval, if the request contains substantiating data to justify the increase for that operator. \n\n\tJ.\tSpecial flight permits may be issued in accordance with Section 21.197 and 21.199 of the Federal Aviation Regulations to operate airplanes to a base for the accomplishment of the inspections and/or modifications required by the AD. \n\n\tK.\tAlternate means of compliance or other actions which provide an equivalent level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region. \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 98124-2207. These documents may be examined at the FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington. \n\n\tAmendment 39-4745 became effective October 27, 1983. \n\tThis Amendment 39-5215 becomes effective February 24, 1986.