60-10-05: Fuel Pressure Relief Valve

60-10-05 LOCKHEED: Amdt. 145 Part 507 Federal Register May 10, 1960. Applies to All Model 188 Aircraft. Compliance required as indicated. There have been reported instances of the main float closure port of the fuel tank vent valve remaining closed due to slight pressure in the tank. These pressures are considerably less than the 1.75 p.s.i. setting of the pressure relief poppet. There is also a possibility of sticking of the pressure relief poppet in the P/N 634056-1 tank vent valves. As a precautionary measure, underwing refueling must be accomplished with the overwing fuel caps removed until the following action has been taken. As soon as possible but no later than the next periodic inspection: (a) Drill a 1/8-inch hole in the suction relief flapper approximately halfway between the center of the flapper and the flapper seat. (b) Manually determine that the pressure relief poppet action is free. Upon accomplishment of above action normal underwing fueling procedures may be resumed. (Lockheed message to all Electra operators dated April 18, 1960, covers this same subject.) This airworthiness directive sent by telegram to all operators of 188 aircraft on April 19, 1960.