48-15-03 DOUGLAS: Applies to C-54 and DC-4 Aircraft. \n\n\tCompliance required by November 1, 1948. \n\n\tBecause of service failures of hydraulic pressure regulator valves, the following must be accomplished: \n\n\t1.\t(a)\tModify Douglas hydraulic pressure regulator valve P/N 5104005, P/N 5231848, or P/N 5327293 to the equivalent of Douglas regulator P/N 5332857, or \n\n\t\t(b)\tConvert Douglas hydraulic pressure regulator valve P/N 5104005, P/N 5231848, or P/N 5327293 to Douglas regulator P/N 5332857, or \n\n\t\t(c)\tInstall Douglas hydraulic pressure regulator P/N 5332857, or \n\n\t\t(d)\tInstall Bendix hydraulic pressure regulator P/N 407484, or \n\n\t\t(e)\tInstall Air Associates hydraulic pressure regulator valve P/N HC-3600, or \n\n\t\t(f)\tInstall Vickers hydraulic pressure regulator valve P/N AA-34551, P/N AA-34552, or P/N AA-34585 which must have the letter "C" or subsequent terminating the regulator serial number, i.e., "Serial No. 0000C," "Serial No. 0000D," etc. \n\n\t2.\tInstall a hydraulic fluid filter with Purolator core in regulators listed in 1, (a) through (d). \n\n\t(Douglas Service Bulletin DC-4 No. 22, "Rework of Hydraulic Pressure Regulator Valve" with addendum, "Optional Installation of Hydraulic Pressure Regulators" covers part 1. Douglas Service Bulletin C-54-239, "Installation of Filter in Hydraulic Regulator Operating Line," covers part 2.)