TM 1-1520-238-10 Change 2 2-35 selected engine crossfeed/shutoff valve automatically closes. Some helicopters have been modified with green and am- ber crossfeed (X FEED) annunciator lights located on the pilot and CPG caution/warning panels (fig 2-44.1). The green X FEED annunicator light will illuminate on both caution/warning panels when crossfeed is selected by the pilot and both engine fuel valves are correctly positioned for the selection. The green X FEED annunicator light will also illuminate when override and crossfeed is selected by the CPG and both valves are correctly positioned. When the CROSSFEED switch on the pilot fuel control panel is placed in the FWD TK or AFT TK position the X FEED caution/warning lights will be inhibited for 3 1 second while the fuel valves move to their selected posi- tion. The amber X FEED annunicator light and the MAS- TER CAUTION light (fig 2-43) will illuminate on both cau- tion/warning panels when the pilot has selected crossfeed or the CPG has selected override and one or both fuel valves are incorrectly positioned. The amber X FEED cau- tion/warning lights will also illuminate when a fuel valve is in the CLOSED position (in response to actuation of a fire handle or pilot fuel control panel ENG 1 or ENG 2 fuel switch in the OFF position. NOTE During engine start the amber X FEED cau- tion/warning lights will illuminate if the CROSSFEED switch is not in the AFT TK position. c. External Tank Switch (EXT TK). The pilot acti- vates fuel transfer from as many as four external fuel tanks to the internal fuel cells by positioning the EXT TK switch to ON. The switch opens the auxiliary fuel tank shutoff valve and the two transfer shutoff valves. Opening the auxiliary fuel tank shutoff valve allows pressurized air to force fuel from the left auxiliary fuel tank into the forward fuel cell and from the right auxiliary fuel tank into the aft fuel cell. When all auxiliary tanks are empty, the EXT EMP caution light on the pilot caution/warning panel illumi- nates. NOTE The REFUEL VALVE switch (located on the external fuel servicing panel (fig 2-45) must be closed for operation of the TRANS switch to be effective. The trans- fer pump will not transfer fuel if the refuel valve is open. The fuel transfer system is the primary method of balancing loads. d. Transfer Switch (TRANS). The TRANS switch controls the position of the fuel transfer air valve. The fuel transfer air valve directs pressurized air to the bi-direction- al transfer pump which allows fuel transfer between fuel cells. With the switch in the TO AFT or TO FWD position, pressurized air is directed to the air motor which turns the transfer pump and transfers fuel forward or aft. If the transfer pump is transferring fuel and the fuel cell to which it is transferring becomes full, a fuel level control valve will shut off the fuel flow through the pump. There is no need to stop the transferring operation until the fuel cells are at the desired level. Some helicopters have been modified with green and am- ber transfer (FUEL XFR) annunciator lights located on the pilot and CPG caution/warning panels (fig 2-44.1). The green FUEL XFR annunicator light will illuminate on both caution/warning panels when the pilot or CPG fuel trans- fer switch is in the transfer position and transfer occurs. The amber FUEL XFR annunicator light and the MASTER CAUTION light (fig 2-43) will illuminate on both caution/ warning panels when the pilot or CPG fuel transfer switch is in the transfer position and transfer does not occur. WARNING The CROSSFEED switch shall be set to the NORM position at all times unless ex- ecuting emergency procedures for FUEL PSI ENG 1 and FUEL PSI ENG 2. Using the fuel system crossfeed may result in a dual engine flameout if one of the engine fuel valves fails to properly position. e. BOOST Switch. The boost pump (located in the aft fuel cell) is used for starting the engines and when the FUEL PSI ENG 1 and FUEL PSI ENG 2 caution lights illu- minate. The BOOST switch electrically opens the boost pump shutoff valve which directs pressurized air to the air driven boost pump. When the switch is in the OFF posi- tion, the engines receive fuel (through a suction feed sys- tem) via the engine-mounted fuel pumps. When the BOOST switch is in the ON position, and the CROSS- FEED switch is in the AFT TK position, both engines feed from the aft fuel cell. The boost pump is automatically started and shut down during the engine start sequence. Shutdown occurs at approximately 52% N_G. It should be noted that the pilot CROSSFEED switch must be in the AFT TK position in order for the BOOST switch to latch on.