Airplane and Engine Fuel System – Boeing 777

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A Description of the Boeing Fuel System

An aircraft consumes fuel in order to supply the energy that is needed to propel it, together with all the cargo that it carries. The energy requirements make it possible for the plane to work efficiently. An aircraft should have an elaborate storage facility for fuel, as well as a good supply model for the fuel, in case there is failure of one of the tanks. The Boeing 777 is a jet airliner that is designed by Boeing Commercial Airplanes. The aircraft has a capacity of 314 to 541 passengers. It has a range of 9,695km to 17,594 km. The aircraft is fuel efficient and maximizes on the fuel consumption compared to the previous models. The Boeing 777 plane has a number of mechanisms for fuel efficiency. Among others, these include:

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Fuel Storage and Capacities

Fuel in the plane is stored in four different tanks, the center tank, the left tank, the right tank and the auxiliary tank. These tanks have the following capacities:

Tank Liters Kilograms
Left Main 38,990 31,300
Right Main 38,900 31,300
Center 103,290 82,900
Auxiliary 7,100 5,700
Total 188,370 151,200

These are the current fuel capacities, although various models of the plane have varying tank capacities. The earlier versions have a lower fuel capacity, but the new versions are more improved as more efficiency is required.

Fuel Monitoring

A number of aspects concerning the fuel are closely monitored. These include fuel quantity and fuel temperature. In order to provide quantity monitoring, each tank has a sensor inside it which closely measures and reflects the amount of fuel available. All the sensors are interconnected and linked up to form one reading. The total amount of fuel in all the tanks is displayed on the fuel synoptic display. The sensors are also able to monitor fuel temperature in the tanks. The state of monitored temperature is indicated on the fuel synoptic display (Ford, 1998).

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Fuel Pumps

Each of the four tanks contains two AC-powered pumps. The pumps are so efficient that a single pump can easily supply enough fuel to power the engine in all conditions. Moreover the two pumps in the center tanks are override pumps, which allows them to pump a higher output than that of the left and right fuel tanks (Langton, Clark, Hewitt, & Richards, 2009). This is important because it ensures that the fuel at the center is pumped continuously and consumed first before the fuel at the sides of the wings is used. Normally, after a low-pressure pumping for around 25 seconds the center pumps shut down. This enables the side wings to take over in supplying the engines with fuel.

Pumping Mechanism

Spitzer (2006) explains that the center pumps are normally in charge as they have a higher pressure than the other pumps. When the main tank switches are off, an alert is given to the pilot. This enables the switching to the right tanks to proceed, thereby supplying more fuel. The other alternative is pressing to allow the functioning of the auxiliary tank. The tank has only one switch, which allows it to empty its contents into the main tank.

The Suction Feed Process

In case the pressure of the pump becomes low, each engine will suck fuel from its corresponding main tanks by using direct connections to the tank without necessarily going through the pump. This saves the engines in case there is a breakdown in the flow of fuel from the tanks or a breakdown in the pumps. It allows the engines to directly suck fuel from the tanks in response to the deficit experienced (Yenne, 2002).

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The Fuel Cross-feed

These are an arrangement of valves which feed into the engine. The valves are arranged in such a way that any of the fuel tanks can pump fuel into the engines. During a normal operation, the valves remain closed (Birtles, 1998). When need arises, the valves are opened to feed the engine from either side. Either valve is enabled to feed the engine from the opposite fuel tank. When the fuel on one side is not working, the cross-feed fuel switch will illuminate, thus enabling the fuel from the valves to be fed into the engines.

The Fuel Imbalance

Balance is the key to an airplane’s stability in the air. Therefore, when an imbalance occurs, it may destabilize the aircraft. Fuel imbalance occurs when the fuel on one side has been used up and a reasonable quantity has been consumed (Spitzer, 2006). This, therefore, causes a necessity to fill the tank full with fuel on one side, while the other side is almost empty. This can be adjusted by balancing the amount fuel. Fuel balancing is normally done by opening the cross-feed from the opposite side, and then turning off the tank that is currently being used. This therefore ensures that fuel is pumped from the full tank, thus causing a balancing effect (Ford, 1998).

How It Works

Fuel Jettison

The fuel jettison system is used to allow supply of fuel to the engines from all the tanks irrespective of the sides in which the tanks are located. The fuel is directed through the jettison nozzle valves, which allow the fuel utilization from all the storage capacities in order to carry out the fuel balancing of the plane (Langton et al., 2009). Fuel jettison is initiated by the FUEL JETTISON ARM. The main tank jettison opens when the following happens:

  1. When the fuel jettison nozzle switches are pushed on.
  2. When the jettison nozzle valves are opened.
  3. When the main tank jettison pumps are opened.

In a different scenario, the center tank fuel will also jettison in case the center tank override pumps are put on. On the other hand, when the pumps are off, the center tank fuel will not in any way jettison. It is also important to note that these nozzles cannot open on the ground irrespective of what happens (Spitzer, 2006). No position of the switch will allow the nozzles to open. During the flight when the plane is in the air, jettison time is normally shown in minutes. The system will automatically shut down the jettison pumps and close the center tank jettison, at the same time isolating the valves.

In trying to understand better fuel systems in the aircraft, it is important to note what language is used for conveying messages. The aircraft model, Boeing 777 is one of the most highly computerized aircrafts in the market. It uses high level of command language in passing or conveying a message about its internal operations to the person operating it. It uses some form of coded language and abbreviations which will communicate to the pilot and co-pilot what needs to be done in order to respond to the command being issued by the aircraft.  The following are some of the most common language words that the Boeing 777 uses to pass information and their meaning (Langton et al., 2009).

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Fuel Auto Jettison- This is a warning note, which simply means that the fuel jettison automation shutoff has malfunctioned or it can even mean that the total quantity of fuel is insufficient. The nozzle valve is open at this point (Yenne, 2002).

  • Fuel Crossfeed Aft, Fwd is an advisory note. It means that the cross-feed valve is not in the commanded position.
  • Fuel Disagree (it is also an advisory note) – it means that the total quantity of fuel and the distance calculated do not match. It is important because it gives warning and advice on fuel refilling.
  • Fuel Imbalance (Advisory Note) – it indicates an existing imbalance between the fuels found in the main tank and the other tanks.
  • Fuel in Center (Advisory Note) – the center fuel pump is off, with a lot of fuel being in the center tank (Yenne, 2002).
  • Fuel jettison nozzle L, R – this means that the jettison nozzle valve is not in the right commanded position.
  • Fuel Low Center – it means that either one or even both pump switches are off or the quantity of fuel at the center is currently low.
  • Fuel Press ENG L, R- this is a caution given because the engine is on suction mode.
  • Fuel Press ENG L+ R, – this is caution given because all the pump output pressures are low and something needs to be done.
  • Fuel pump L, aft, fwd this is a caution that is given by a beep. This normally indicates that the left aft or the forward pressure of the forward pump is low.
  • Fuel Pump R, AFT, and FWD – This usually displays that the left aft or the forward pressure of the forward pump is low.
  • Fuel Qty Low- this is an advice-giving note that the fuel quantity is low in both of the main tanks.
  • Fuel Temp Low: this gives an indication to the pilot that the fuel temperature is now approaching the minimum.
  • Fuel Valve APU- it is an advice that reveals that the APU fuel valve is not in the commanded position (Spitzer, 2006).

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The Boeing 777 is an ultramodern plane. It has been built to efficiently manage fuel. The plane is made in a fuel-economic manner. Moreover, there have been numerous improvements from the earlier versions that were made in the late 1900s. The plane has been designed to counter any forthcoming shortage of fuel supply, utilizing all the available reserves of fuel in order to prevent any impending tragedy that might arise due to shortage of fuel. This makes it the best plane for consideration in the modern world where much attention is paid to fuel efficiency.

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