48-03-02 DOUGLAS: Applies to All Models C-54-DC and DC-4 Aircraft. \n\nIn order to prevent the emergency air brake valve front seizing due to infrequent operation, the following should be conducted: \n\nAt intervals not to exceed 1,000 hours, except at the discretion of the CAA Agent, the interval may be increased to coincide with a regular overhaul period, but should in no case exceed 1,700 hours. \n\nConnect a gage to one brake port on each side of the airplane and discharge the air brake cylinder from one of the flight compartment controls. The initial air pressure indications on the gages at the brakes should not be less than 400 p.s.i. Allow 5 minutes for change in pressure due to temperature and again note the air pressure indications on the gages at the brakes. These second observed pressure indications should hold steadily for a period of at least 5 minutes. This will check the functioning of one of the pull mechanisms, the air brake control valve, shuttle valve, linesand fittings. Push in the control to release air pressure on brakes and operate other air brake control to insure that both pull mechanisms are operating properly.