Figure 14-17.  A simple high-wing fuel injection fuel system for a light twin reciprocating-engine aircraft.  Left inboard  Left outboard OFF Rightinboard Right outboard OFF Selector valves Electric fuel pump Injection nozzles Fuel injection distributor manifold Fuel injection metering unit Strainers Fuel supply Pump delivery Metered fuel pressure Jet transport fuel systems can be regarded as a handful of  fuel subsystems as follows: drainage of fuel back into the main tanks. Surge tanks are  also use for fuel system venting. Transport category fuel systems require venting similar to  reciprocating engine aircraft fuel systems. A series of vent  tubing and channels exists that connects all tanks to vent space  in the surge tanks (if present) or vent overboard. Venting must  be configured to ensure the fuel is vented regardless of the  attitude of the aircraft or the quantity of fuel on board. This  sometimes requires the installation of various check valves,  float valves, and multiple vent locations in the same tank.  Figure 14-20  shows the fuel vent system of a Boeing 737. Most transport category aircraft fuel systems are very much  alike. Integral fuel tanks are the norm with much of each  wing’s structure sealed to enable its use as a fuel tank. Center  wing section or fuselage tanks are also common. These may  be sealed structure or bladder type. Jet transport aircraft carry  tens of thousands of pounds of fuel on board.  Figure 14-19 shows a diagram of a Boeing 777 fuel tank configuration  with tank capacities. A transport category aircraft fuel distribution subsystem  consists of the pressure fueling components, defueling  components, transfer system, and fuel jettison or dump  system. Single-point pressure fueling at a fueling station accessible by ramp refueling trucks allows all aircraft fuel  tanks to be filled with one connection of the fuel hose.  Leading and trailing edge wing locations are common for  these stations.  Figure 14-21  shows an airliner fueling station  with the fueling rig attached.  Note that there are optional fuel storage configurations  available on the same model airliner. For example, airlines  expecting to use an aircraft on transoceanic flights may  order the aircraft with long-range auxiliary tanks. These  additional tanks, usually located in the fuselage section of  the aircraft, can alter fuel management logistics in addition  to complicating the fuel system. To fuel with pressure refueling, a hose nozzle is attached  at the fueling station and valves to the tanks required to be  filled are opened. These valves are called fueling valves  or refueling valves depending upon the manufacturer’s  preference. Various automatic shutoff systems have been  designed to close tank fueling valves before the tanks overfill  or are damaged. Gauges on the refueling panel allow refueling  personnel to monitor progress.  In addition to main and auxiliary fuel tanks, surge tanks may  also be found on jet transports. These normally empty tanks  located in the wing structure outboard of the main wing tanks  are used for fuel overflow. A check valve allows the one-way  1. Storage 2. Vent 3. Distribution 4. Feed 5. Indicating 14-14