78-01-16 MCDONNELL DOUGLAS: Amendment 39-3117. Applies to Model DC-9 and Military C-9 Series Airplanes certificated in all categories, Fuselage Numbers 1 through 851, inclusive which correspond to the factory serial numbers listed in Douglas DC-9 Service Bulletin No. 54-31, dated August 24, 1976, or later FAA approved revisions. \n\n\tTo detect cracks and prevent possible failure of the engine pylon aft upper spar straps (caps) comply with the following: \n\n\t(a)\tFor airplanes with 35,000 or more landings on the effective date of this AD, within the next 600 landings unless already accomplished within the last 1800 landings and thereafter at intervals not to exceed 2400 landings, accomplish Paragraph (f). \n\n\t(b)\tFor airplanes with 30,000 to 34,999 landings on the effective date of this AD, within the next 900 landings, unless already accomplished within the last 1500 landings, and thereafter at intervals not to exceed 2400 landings, accomplish Paragraph (f). \n\n\t(c)\tFor airplanes with 25,000 to 29,999 landings on the effective date of this AD, within the next 1200 landings, unless already accomplished within the last 1200 landings, and thereafter at intervals not to exceed 2400 landings, accomplish Paragraph (f). \n\n\t(d)\tFor airplanes with 15,000 to 24,999 landings on the effective date of this AD, within the next 2,000 landings, unless already accomplished within the last 400 landings, and thereafter at intervals not to exceed 2400 landings, accomplish Paragraph (f). \n\n\t(e)\tFor airplanes with less than 15,000 landings on the effective date of this AD, within the first 2,000 landings, after accumulating 15,000 landings, and thereafter at intervals not to exceed 2400 landings, accomplish Paragraph (f). \n\n\t(f)\tAs required by Paragraphs (a) through (e): \n\n\t\t(1)\tUltrasonically inspect the engine pylon aft upper spar straps (caps), Part Number 9958154-5/-6 or 9958154-37/-38 per Paragraph 2.B of Douglas DC-9 Service Bulletin A54-31 dated December 22, 1976 orlater FAA approved revision, or an alternate method approved by the Chief, Aircraft Engineering Division, Western Region. If there is evidence of cracking, magnetic particle inspection per Paragraph 2.C may be used to confirm the evidence of cracking. \n\n\t\t(2)\tIf cracks are detected, before further flight replace the strap with new Part Numbers 9958154-5/-6 or 9958154-37/-38 and resume the inspections after the part has accumulated 15,000 landings or modify in accordance with Douglas Service Bulletin 54-31 dated August 24, 1976 or later FAA approved revision. \n\n\t\t(3)\tAt the option of the operator, the ultrasonic inspection may be deleted if the magnetic particle inspection is accomplished. If the magnetic particle inspection procedure is used, after two bearing replacements it is necessary to replace the strap with a new Part Number 9958154-5/-6 or 9958154-37/-38 or modified per Douglas Service Bulletin 54-31 dated August 24, 1976 or later FAA approved revision. \n\n\t(g)\tUpon completion of modification of the engine pylon rear spar straps (caps) per Douglas Service Bulletin 54-31 dated August 24, 1976 or later FAA approved revision the inspection requirements of this AD are terminated. \n\n\t(h)\tFor the purpose of complying with this AD, if records of landings are not available, the number of landings for the purpose of establishing initial compliance may be determined by dividing each airplane's hours in service by the operator's appropriate fleet average time from takeoff to landing. This procedure is subject to acceptance by the assigned FAA maintenance inspector. \n\n\t(i)\tSpecial flight permits may be issued in accordance with FAR's 21.197 and 21.199 to authorize operation of an airplane to a base for the accomplishment of the inspections required by this AD. \n\n\tThis Amendment becomes effective February 13, 1978.