86-16-05 BOEING: Amendment 39-5379. Applies to Model 747 series airplanes listed in Boeing Service Bulletin 747-53-2220, Revision 1, dated October 10, 1983, certificated in any category. \n\n\tTo detect corrosion in the aft pressure bulkhead web and lower chord accomplish the following unless already accomplished: \n\n\tA.\tPerform an inspection for corrosion of the aft pressure bulkhead lower web and the lower chord of Body Station 2360 bulkhead in accordance with Boeing Service Bulletin 747- 53-2220, Revision 1, dated October 10, 1983, or later FAA-approved revisions, in accordance with the following schedule after the effective date of this AD: \n\n\t\t1.\tWithin 6 months for airplanes that have accumulated over 40,000 flight hours on the effective date of this AD; \n\n\t\t2.\tWithin 12 months for airplanes that have accumulated 20,000 to 40,000 flight hours on the effective date of this AD; and \n\n\t\t3.\tWithin 24 months or upon the accumulation of 20,000 flight hours, whichever occurslater. \n\n\tB.\tFor airplanes on which the aft pressure bulkhead lower web and the lower chord of Body Station 2360 bulkhead have not been modified with the reworked drain hole, application of leveling compound, trimming of insulation blanket, and an application of corrosion preventive compound in accordance with Boeing Service Bulletin 747-53-2220, Revision 1, dated October 10, 1983, or later FAA-approved revisions, repeat the inspections required by paragraph A., above, at intervals not to exceed three and one-half years. \n\n\tC.\tFor airplanes on which the aft pressure bulkhead lower web and the lower chord of Body Station 2360 bulkhead have been modified with the reworked drain hole, application of leveling compound, trimming of insulation blanket, and an application of corrosion preventive compound in accordance with Boeing Service Bulletin 747-53-2220, Revision 1, dated October 10, 1983, or later FAA-approved revisions, repeat the inspections required by paragraph A., above, at intervals not to exceed seven years. \n\n\tD.\tIf any corrosion is found in the aft pressure bulkhead lower web and the lower chord of Body Station 2360 bulkhead, repair before further flight in accordance with Boeing Service Bulletin 747-53-2220, Revision 1, dated October 10, 1983, or later FAA-approved revisions. \n\n\tE.\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\tF.\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes unpressurized to a base for the accomplishment of inspections and/or modifications required by this AD. \n\n\tAll persons affected by this directive who have not already received the appropriate service information from the manufacturer may obtain copies upon request to the Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124-2207. This document 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\tThis amendment becomes effective September 10, 1986.