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When the FRTT valve is open, fuel returns to the wing tank through the recirculation line. Heated fuel is then distributed to the number 1 and 2 cell of the wing fuel tank. No fuel is distributed to the number 3 cell as it will have emptied before the local fuel temperature reaches .40°C (F). The recirculation line is fitted with a check valve to prevent crossflow or fuel propagation due to a ruptured line. The wing fuel tanks are fitted with many fuel temperature sensors; the left wing has two and the right wing has three. With the Fuel Recirculation OFF, the Fuel Management and Quantity Gauging Computer (FMQGC) reads all temperature sensor but will display only the lowest temperature. When the Fuel Recirculation system is ON, the FMQGC computer reads the inboard temperature sensor as it will be the one who reads the highest temperature. Operation of the Fuel Recirculation System is allowed only during cruise flight above 34,000 feet. Display of system status is provided through EICAS messages. A L (R) FUEL RECIRC FAIL caution message will be displayed on the EICAS status page when the FRTT valve is not in the commanded or allowed position. Finally, the L (R) FUEL RECIRC OFF status message will be displayed when the crew selects system off. The FUEL HI TEMP caution message is posted when the bulkhead fuel temperature exceeds 54°C when the Fuel Recirculation System is inoperative. To prevent the system from operating above the freezing level, the set point has been reduced to 10°C when the system is selected on. Rev 2A, Apr 11, 2005 Flight Crew Operating Manual Volume 2
FUEL VALVE TS Temperature Sensor The FRTT valves are powered by their dedicated circuit breakers on DC BUS 1 and 2. FUEL FILTERS, QUANTITY AND TEMPERATURE READOUTS
Amber . Engine fuel temperature is < 5°C .
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