55-11-01 DOUGLAS: Applies to All DC-6 Aircraft; DC-6A Through Fuselage No. 543; DC-6B Through Fuselage No. 590; DC-7 Through Fuselage No. 566 (Except Fuselage No. 486); and C-18A Airplane Serial Number 42881 (Fuselage No. 29). \n\n\tCompliance required as indicated. \n\n\tAs a result of recent landing accidents in which the nose landing gear collapsed due to failure at the end fitting of yoke P/N 5488450 on a DC-7 and yoke P/N 524570 on a DC-6, and as a result of fatigue cracks being found on subsequent inspections of DC-6 Series as well as DC-7 aircraft, the following inspections must be accomplished at intervals not to exceed 500 hours of operation and should be included as part of any major inspection necessitated by overweight or hard landing. \n\n\t1.\tRemove the bolts from the two upper spot-faced holes in the L.H. and R.H. flanges of the nose gear yoke. P/N 5245790 is used on DC-6 Series aircraft and P/N 5488450 is used on DC-6 Series and DC-7 aircraft. \n\n\t2.\tInspect the bolt holes and radius of the spot face for signs of cracks by means of dye penetrant or equivalent. To obtain good results with dye penetrant inspection, it may be necessary to heat the parts being inspected to 90-100 degrees F. To facilitate the dye to penetrate the cracks. Also inspect the surface at the end of the 1/2-inch radius where the end flange blends into the cylindrical portion of the yoke. \n\n\t3.\t(a)\tIf cracks are found the part must be replaced with P/N 5488450-503 or with new parts P/N 5538558 for DC-6 Series and P/N 5538557-1 for DC-7 and DC-7B aircraft. \n\n\t\t(b)\tIf no cracks are found, and as an interim measure, the old nose gear yoke assemblies P/N 5235790 and 5488450 may be reworked by remachining the spot faces to incorporate a 0.125-inch radius and reworking the 1/2-inch radius of the yoke, when necessary, in accordance with paragraphs 3 and 4 of DC-6 Service Bulletin No. 607 or DC-7 Service Bulletin No. 56 mentioned below. After remachining, shotpeen the spot face radii, the flange and radius where flange blends into the cylindrical portion of the yoke, then clean and apply protective finish. When parts are reworked, as described above, they should be reinstalled using special large washers in accordance with the pertinent Service Bulletin. The inspections outlined in paragraph 2 must be continued on these reworked parts until they are replaced with parts listed in paragraph 3(a). \n\n\t4.\tWhen cracked or reworked parts have been replaced with new parts mentioned in paragraph 3(a) the special inspections required in paragraph 2 may be discontinued. \n\n\t(Douglas Service Bulletin No. 607 dated July 22, 1955, for DC-6 Series and Service Bulletin No. 56 dated July 22, 1955, for DC-7 cover the above.) \n\n\tThis supersedes AD 55-07-01 and those portions of AD 55-10-01 which cover this same subject.