CHAPTER 4. Powerplants Fuel Systems The fuel system is designed to provide an uninterrupted fl ow of clean fuel from the fuel tank to the engine. See Chapter 3, Components and Systems, for more information on fuel tanks. See earlier section in this chapter for specifi cs on fuel injection systems. The fuel must be available to the engine under all conditions of engine power, altitude, attitude, and during all approved fl ight maneuvers. [Figure 4-17] Fuel Pumps WSC aircraft with carburetors have engine-driven fuel pump systems. A diaphragm pump is the primary pump in the fuel system for two-stroke engines. Air pulses in the crankcase actuate a diaphragm and provide fuel under pressure to the carburetor. Four-stroke engines have a mechanical pump driven directly off the engine. Sometimes an electric auxiliary pump is provided for use in engine starting and in the event the engine pump fails. The auxiliary pump, also known as a boost pump, provides added reliability to the fuel system. The electric auxiliary pump is controlled by a switch in the fl ight deck.

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