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Engine system reliability can be improved by advanced electric architectures, while the reduction of hydraulic components, fuel tubes, and fittings can enhance the maintainability of the engine and minimize pilot workload.

In the integrated fuel system study for an assumed single-aisle aircraft, it was estimated that the aircraft boost pumps, engine FMUs, and MFPs (main fuel pumps) in the conventional system would be replaced by four sets of electric fuel pump units. In addition, with the cross feed valves and aircraft shutoff valves removed, the total number of LRUs (line replacement units) in the integrated aircraft system is expected to be reduced to about half of the conventional system.

The proposed integrated system eliminates electric valves such as the cross feed and shutoff valves as much as possible. However, in considering emergency situations—for example, severe fuel leakage from anywhere in the system—isolation of the fuel system may be required to avoid loss of the aircraft fuel. For that purpose, the addition of monitoring devices such as fuel pressure sensors, leak detectors, and electric shutoff valves may be considered. Also, if the aircraft system wants to control the fuel amount in the left and right tanks independently, that would be accomplished by the addition of the electric shutoff valves in the system. Thus, the proposed integrated electric fuel system has the flexibility to incorporate additional electric devices and will support aircraft system requirements.

As mentioned above, the reduction in the number of LRUs will be achieved by introduction of the integrated fuel system. In addition, components that are submerged in the aircraft fuel tanks, such as the aircraft boost pumps, will be removed. One possible location for the electric fuel pump units is the fuselage, inside of the access door.

Currently, LRUs are installed into distributed locations among the aircraft wing, aircraft tank, and the engine. In the integrated system, the LRUs may be installed in one place in the aircraft fuselage, so that replacement of the pump unit will be much easier than the current aircraft/engine fuel system components. Reduction in the number of LRUs, accessibility, and replaceability of the electric pump unit will improve the maintainability of the aircraft/engine fuel system.

Because the integrated system allows for the removal of the cross feed valves, adjustment of the tank balance by pilots would not be necessary anymore. On/off of the current submerged aircraft boost pumps is usually conducted by pilots to maintain a minimum amount of fuel in the tank, which is previously determined to avoid heating of the pump.

In the proposed integrated fuel system, the electric fuel pump units would be installed outside of the fuel tank, instead of the submerged boost pumps. Pilot operation for the cross feed valves or boost pumps would not be necessary; thus, reduction of pilot workload would be expected.

This article is based on SAE International technical paper 2013-01-2080 by Noriko Morioka IHI Corp. and Hitoshi Oyori, IHI Aerospace Co.