66-01-01\tBOEING: Amdt. 39-176 Part 39 Federal Register January 5, 1966. Applies to Models 720 and 720B Series Airplanes. \n\n\tCompliance required as indicated.\n \n\tTo prevent further cracking in the wing upper surface skin, accomplish the following: \n\n\t(a)\tFor airplanes with less than 10,000 hours' time in service on the effective date of this AD, comply with (c) before the accumulation of 10,300 hours' time in service, unless accomplished after the accumulation of 9,700 hours' time in service, and thereafter at intervals not to exceed 600 hours' time in service from the last inspection.\n \n\t(b)\tFor airplanes with 10,000 or more hours' time in service on the effective date of this AD, comply with (c) within the next 300 hours' time in service after the effective date of this AD, unless accomplished within the last 300 hours' time in service, and thereafter at intervals not to exceed 600 hours' time in service from the last inspection.\n \n\t(c)\tInspect the wing upper surface skinfor cracks in accordance with Paragraph 3, Part I, "Inspection Data" of Boeing Service Bulletin No. 2309, Revision 2, or later FAA-approved revision.\n\n\t(d)\tIf cracks are detected during the inspections required by (c), before further flight, accomplish an x-ray inspection of the area from stringer No. 8 to the rear spar on both wings in accordance with "Process Data" included in Boeing Service Bulletin No. 2309, Revision 2, or later FAA-approved revision, or an equivalent approved by the Chief, Aircraft Engineering Division, FAA Western Region.\n \n\t(e)\tFor airplanes with less than 7,000 hours' time in service on the effective date of this AD, comply with (g) before the accumulation of 8,800 hours' time in service, unless accomplished after the accumulation of 6,800 hours' time in service, and thereafter at intervals not to exceed 2,000 hours' time in service from the last inspection. \n\n\t(f)\tFor airplanes with 7,000 or more hours' time in service on the effective date of this AD, comply with (g) within the next 1,800 hours' time in service after the effective date of this AD, unless accomplished within the last 200 hours' time in service, and thereafter at intervals not to exceed 2,000 hours time in service from the last inspection. \n\n\t(g)\tAccomplish an x-ray inspection of all concealed areas on each wing in accordance with "Process Data" included in Boeing Service Bulletin No. 2309, Revision 2, or later FAA- approved revision, or by an equivalent approved by the Chief, Aircraft Engineering Division, FAA Western Region. \n\n\t(h)\tIf a crack is detected during the inspections conducted in accordance with (c), (d), or (e), before further flight, repair the skin crack, in accordance with Paragraph 3, Part II, "Interim Repair Data", or Part III, "Permanent Repair Data", Boeing Service Bulletin No. 2309, or later FAA-approved revision, or an equivalent approved by the Chief, Aircraft Engineering Division, FAA Western Region. Cracks repaired in accordance with Interim Repair Data shall be inspected: at intervals not to exceed 35 hours' time in service until the Part III Permanent Repair is accomplished if the repaired cracks are visible or, if x-ray inspection is required and the cracks are 1.25 inches in length or greater; or, at intervals not to exceed 150 hours' time in service until the Part III Permanent Repair is accomplished if the repaired cracks are concealed, x-ray inspection is required, and the cracks are less than 1.25 inches in length. When the Part III Permanent Repair has been accomplished, the repetitive inspections required by this AD may be discontinued.\n \n\t(i)\tUpon request of an operator, an FAA maintenance inspector with prior approval of the Chief, Aircraft Engineering Division, FAA Western Region, may adjust the repetitive inspection intervals required by the AD to permit compliance at an established inspection period of the operator if the request contains substantiating data to justify the increase for that operator.This supersedes AD 65-27-01. \n\n\tThis directive effective January 5, 1966.