Left aux.  fuel tank (opt.) Right aux. fuel tank (opt.) Left fuel tank Right fuel tank AUX LEFT RIGHT OFF AUX LEFT RIGHT OFF Selector valve Right engine fuel pump to heater Fuel pressure adjusting screw Drain control Strainer Right oil  dilution solenoid To right engine oil pump On/off prime Vapor return line Drain valve Vapor separator Right engine fuel control unit To right aux. pump Fuel pressure switch for aux.  pumps Aux. fuel pump Drain valve Aux pump Vent Vent in filler cap Drain valve Filler cap Fuel injection nozzle Right engine fuel manifold To cylinders To cylinders Dual fuel flow gauge Ignition switches Drain plugs Fuel quantity indicator Aux. tank fuel quantity indicator Drain plugs Throttle Mixture control Vent in filler cap Filler cap Drain valve Vent Drain valve Aux fuel pump Selector valve Drain control Vapor return line Drain valve Strainer To left engine oil pump Left oil  dilution solenoid Vapor separator Left engine fuel pump Fuel pressure adjusting screw On/off prime Throttle Mixture control To left aux. pump Fuel pressure switch for aux.  pumps Left engine fuel control unit Left engine fuel manifold To cylinders To cylinders Fuel injection nozzle Filter screen Filter screen CODE Fuel Vapor return line Mechaninal actuation Electrical actuation Check valve Pressure relief valve Figure 14-16.  A low-wing, twin-engine, light aircraft fuel system. Jet Transport Aircraft Fuel Systems 14-13 Fuel systems on large transport category jet aircraft are  complex with some features and components not found in  reciprocating-engine aircraft fuel systems. They typically  contain more redundancy and facilitate numerous options  from which the crew can choose while managing the  aircraft’s fuel load. Features like an onboard APU, single  point pressure refueling, and fuel jettison systems, which  are not needed on smaller aircraft, add to the complexity of  an airliner fuel system.  Not all large, old aircraft have this fuel system. This is merely  an example. Other aircraft share similar features and possess  unique features of their own. The same is true for small  reciprocating-engine aircraft. There are many systems that  share features with those described above, but they also differ  in some ways. Always consult the manufacturer’s data when  working on aircraft fuel systems and follow all instructions  for service and repair. The fuel system of an aircraft provides  the life blood for engine operation and must be maintained  with the highest discretion. tapped in downstream of the engine-driven fuel pump alerts  the crew should fuel pressure decline.