48-29-01 NAVION: Applies to All Airplanes Employing Carter Engine Driven Fuel Pumps Not Presently Equipped With Vent Drain Lines.
To be accomplished as soon as possible but not later than October 15, 1948.
Several instances of rupture of the main diaphragm of Carter fuel pumps have occurred. This is considered a fire hazard, since fuel can then squirt from the pump breather hole onto the engine. To correct this condition the pump breather should be provided with an overboard drain to carry fuel clear of the airplane if the diaphragm ruptures. Before installing the drain line, the fiber screen and snap ring must be removed from the pump breather opening. The drain line should vent into a low pressure area so that any fuel leaving this drain will not be in the proximity of any engine or cabin heater exhaust and will not contact the airplane or enter any air intake line, in ground or flight operation.
(Ryan Navion Service Letter No. 47 covers this same subject.)