54-06-01 DOUGLAS: Applies to Models DC-6, DC-6A and DC-6B Series Aircraft. \n\n\tCompliance required as soon as practicable but not later than July 1, 1954, for DC-6A and DC-6B aircraft, and November 1, 1954, for DC-6 aircraft. \n\n\tTo eliminate possible inadvertent discharge of CO2 into cabin heater or hydraulic accessories compartment accompanied by operation of cabin master depressurization control (or closing of the control valve on early DC-6 aircraft), when discharging CO2 into a nacelle, rework the two Kidde 3/4-inch stop valves P/N 870003 by replacing spring P/N 201496 with heavier spring P/N 30568. The reworked valve should be reidentified as P/N 871107. \n\n\t(Douglas General Service Letter No. DC-6 No. 176 revised December 31, 1953, also covers this subject.)