Fuel management is an important part of piloting an airplane. Whether commercial or civilian, practically all airplanes burn fuel for thrust. A typical Boeing 737 burns about a quarter-gallon of jet fuel per second, whereas larger airplanes like the Boeing 747 burn a gallon of jet fuel per second. To better manage the available fuel, many airplanes are equipped with a crossfeed system.
The Basics of Crossfeed Systems
A crossfeed system is a fuel management system that’s designed to transfer or “feed” fuel from one tank to an engine on the opposite side of the airplane. In other words, it makes all fuel tanks available to all engines.
Most airplanes don’t have a single fuel tank. Instead, they have multiple fuel tanks, which are typically strategically placed to balance the airplane’s weight. Some airplanes have two fuel tanks — one on each side. Others, though, have over a dozen fuel tanks. Regardless, a crossfeed system ensures that the airplane’s engines can access fuel from far-away tanks.
The Importance of Crossfeed Systems
Why do airplanes have crossfeed systems exactly? While Pilot’s Operating Handbooks (POHs) often have strict requirements regarding when and how they can be used, some allow crossfeed systems to correct weight imbalances. If an airplane with multiple engines burns fuel at different rates, it can create uneven loads. Crossfeed systems solve this problem by redistributing fuel consumption.
Even if a particular POH doesn’t allow crossfeed systems to correct weight imbalances, it may allow for emergency situations. Fuel pumps, for instance, can fail. When this occurs, the engine to which the pump is connected will lose fuel pressure and, thus, it’s ability to generate thrust. A crossfeed system offers a solution. It will transfer fuel from another tank with a different fuel pump to the affected engine.
Parts of a Crossfeed System
While there are different types of crossfeed systems, many of them feature the same basic parts. The crossfeed valve is responsible for opening and closing the fuel connection. When open, it allows fuel to flow from a tank to the engine.
In addition to a crossfeed valve, crossfeed systems often have check valves. Check valves are designed to prevent fuel from flowing backward. They essentially isolate sections of the system to ensure that fuel only moves forward to the intended engine.
Crossfeed systems, of course, have fuel lines. These heavy-duty lines serve as a conduit for fuel. Jet fuel can travel from a tank to the engine by traveling through a given fuel line.