10–7. SYSTEM DESCRIPTION (cont)

TM 1-1520-238-T-7 10–51 10–7. SYSTEM DESCRIPTION (cont) 10–7 g. Auxiliary Fuel System. (1) Purpose. The purpose of the auxiliary fuel system is to transfer additional fuel from auxiliary tanks to internal fuel cells. (2) System Operation (fig. 10–26). (a) The cap assembly provides fueling access to the gravity filler port. When the pilot’s FUEL panel EXT TK switch is placed to ON, the auxiliary fuel tank air shutoff valve and auxiliary tank fuel shutoff valves are opened. PAS air pressurizes the fuel, forcing fuel flow through auxiliary tank fuel shutoff valves into the internal fuel cells. When four external fuel tanks are used, the PAS air is connected only to the outboard auxiliary fuel tanks. The fuel is forced from the outboard fuel tanks, through the inboard fuel tanks, into the internal fuel cells. When the internal fuel cells are full, automatic fuel shutoff occurs, terminating fuel flow. The fuel empty switches complete a circuit when the fuel level is below the float, lighting the EXT EMP indicator on the pilot caution/warning panel. Disconnect couplings are used for jettison capabilities of the external fuel tanks. FUEL TRANSFER SHUTOFF VALVE COUPLINGS PULLAWAY AUXILIARY FUEL TANK(S) RIGHT SIDE PAS AIR AUXILIARY FUEL TANK(S) LEFT SIDE PULLAWAY COUPLINGS WING CONNECTION EMPTY SWITCH GRAVITY FILLER PORT (CAP) EMPTY SWITCH FUEL TRANSFER SHUTOFF VALVE M70-217 GRAVITY FILLER PORT (CAP) Figure 10–26. Auxiliary Fuel Tank Transfer System Interface Diagram (b) Electrical power (fig. 10–27) is supplied through FUEL TRANS circuit breaker (CB56) to the external EXT TK switch on the pilot FUEL panel. When the EXT TK switch is in the OFF position, 28 VDC is applied through contacts 2 and 1 to close the auxiliary tank shutoff valves. When the EXT TK switch is in the ON position, 28 VDC is applied through contacts 2 and 3 to open the auxiliary tank shutoff valves and the auxiliary tank air shutoff valve. Contacts 5 and 6 complete a ground path for the EXT EMP indicator on the pilot’s caution/warning panel. The EXT EMP indicator will light only when both fuel empty switches are below the float level. When four external fuel tanks are used, the fuel empty switches are connected only to the inboard auxiliary fuel tanks.