58-15-01: Safety Belt Hook Assembly

58-15-01 DOUGLAS: Applies to DC-6 and DC-7 Series Aircraft. \n\n\tCompliance required by September 1, 1958. \n\n\tHook assemblies, P/N CSS1000-D, installed in safety belt assemblies, P/N 5610175, have been found to be understrength due to improper heat treat by the vendor. \n\n\tAll DC-6 and DC-7 Series aircraft equipped with these safety belt assemblies that were manufactured during the months of December 1957, January 1958, and February 1958, are affected. These belts can be identified by the manufacturing date (month and year) stamped on the part number tag sewn on the belt (i.e., date manufactured, December 1957, etc.). Belt assemblies manufactured prior to these dates are satisfactory and all future DC-6 and DC-7 aircraft will have safety belts with proper hook assemblies installed. \n\n\tAll hook assemblies that give a Rockwell reading of 36 or above on the "C" scale are satisfactory. Those that show a Rockwell reading below 36 are unsatisfactory and the belt must be replaced.(Douglas Alert Service Bulletin A-779 for the DC-6 Series and A-321 for the DC-7 Series cover the above subject and describe acceptable inspection and replacement procedures.)