49-11-01 NAVION: Applies to Airplanes Equipped With Carter Fuel Pumps Continental P/N 530509 (Carter M687-S and M688-S) or Continental P/N 50375.
To be accomplished as soon as possible but not later than April 15, 1949.
Due to Carter fuel pump lower diaphragm failures, caused by diaphragm deterioration due to excessive pump temperatures when pumps are run dry, the two Carter pumps should be connected in series to insure that fuel will be continuously flowing both pumps and that the pumps will not overheat.
It is therefore required that all parallel Carter pump fuel systems be converted to the series pump arrangement, or, as an alternative, that either an approved Ryan fuel system incorporating an Adel electric booster pump or an equivalent approved fuel system be installed.
Ryan Navion Field Service Bulletin No. 7 also covers this subject and describes means for connecting the fuel pumps in series. In addition, the daily inspections for looseness of the pump lower bowl, which are specified in section II of Ryan's Bulletin No. 7, should be continued.
This supersedes AD 48-40-01.