Ameer Randolph
The Boeing 747 is known for its large fuel tank, which takes up the entire wingspan of the plane. The 747-100 and 747-400 models have a center wing tank (CWT), which is located within the fuselage. The 747-8, the latest variant, has reduced reliance on wing tanks compared to earlier models, but it is unclear whether it has a CWT. Early 747s had a central tank, but by the 1990s, they were rarely used due to safety concerns.
| Characteristics | Values |
|---|---|
| Fuel tank size | Large enough to take up the entire wing span of the plane |
| Number of fuel tanks | Multiple tanks in each wing, with one in the vertical stabilizer |
| Fuel tank material | Metal, usually aluminum alloy, stainless steel, or other fuel-resistant materials |
| Fuel tank pressure | Metal fuel tanks must withstand an internal test pressure of 24 kPa (3.5 psi) without failure or leakage |
| Fuel tank ventilation | Fuel tanks are vented to air to avoid a vacuum when fuel is pumped out |
| Fuel pump motors | 115/220-V induction motors and/or 28 V DC brush motors |
| Fuel-air mixture ignition sources | Static electricity, electrical arcing, pumps, wiring, measuring probes, level sensors, etc. |
| Notable incidents | 1994 Philippine Airlines bombing, 1996 TWA disaster, Swiss Air Flight 111 crash |
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What You'll Learn
- The Boeing 747's fuel tank takes up the entire wing span of the plane
- The 747-8 has reduced reliance on wing tanks compared to previous models
- The 747-100 has a wing center section and CWT
- The 747-131's center wing tank exploded over the Atlantic Ocean in 1996
- The 747's center wing tank is located inside the fuselage
The Boeing 747's fuel tank takes up the entire wing span of the plane
The Boeing 747 is a wide-body commercial airliner that uses wing tanks to store fuel. The wings of the 747 are designed to store large volumes of liquid fuel, with multiple tanks in each wing. The aircraft's fuel tank is so large that it takes up the entire wingspan of the plane.
The 747's fuel system includes a center wing tank (CWT) located within the fuselage, in addition to the wing tanks. This center tank is considered part of the wing structure and is used to store fuel. The use of wing tanks in aircraft is common, especially in larger planes like the 747, due to the natural formation of large enclosed spaces within the wings that are ideal for fuel storage.
The center wing tank in the 747 has been associated with safety concerns due to its proximity to the fuselage. In the 1990s, there were two notable incidents involving the center wing tank: the 1994 Philippine Airlines bombing and the 1996 TWA disaster. While the center wing tanks were present in early 747s, they were rarely used by the 1990s.
The latest variant of the 747, the 747-8, has reduced its reliance on wing tanks compared to earlier models. This reduction is attributed to a redesigned wing structure and more efficient engines, allowing for extended range without the need for additional fuel capacity in the wings.
The fuel tanks in the 747, particularly the center wing tank, have been the subject of safety concerns due to the risk of fire and explosion. Fuel tanks, especially when located within the fuselage, must adhere to strict standards to prevent fuel leakage and withstand emergency landing conditions. The mixture of fuel vapour and air in the tanks, known as the ullage, poses a potential explosion hazard that requires careful management.
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The 747-8 has reduced reliance on wing tanks compared to previous models
The Boeing 747 is a large aircraft with a fuel tank that takes up the entire wingspan of the plane. The fuel tank is made up of multiple tanks in each wing, with the pilots able to move fuel around to trim the aircraft. The 747 also has a central tank, or center wing tank (CWT), which is located inside the fuselage.
Early 747s utilized the central tank, but by the 1990s, they were rarely used. This change in usage was due to safety concerns, as the central location of the tank posed a significant risk of explosion and fire hazards. Notable incidents involving the central tank include the 1994 Philippine Airlines bombing and the 1996 TWA disaster, which was caused by the ignition of fuel vapour in the mostly empty central tank.
The 747-8, the latest variant of the aircraft, has reduced its reliance on wing tanks compared to previous models. This reduction is due to a redesigned wing structure and more efficient engines, allowing for extended range without needing additional fuel capacity in the wings. The raked wingtips of the 747-8 are an example of this redesign, as they are a light, thin composite structure that does not contain fuel.
The reduction in the reliance on wing tanks in the 747-8 has improved safety by minimizing the amount of fuel stored in the wings. This design choice reduces the risk of fuel tank explosions and fire hazards, which have been a concern with earlier models of the 747.
Overall, the 747-8's reduced dependence on wing tanks is a significant improvement, allowing for greater range and improved safety when compared to previous models of the aircraft.
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The 747-100 has a wing center section and CWT
The 747-100 is a variant of the Boeing 747 aircraft. The 747-100 has a total of seven fuel tanks, including a center wing tank (CWT). The CWT is located within the wing center section of the aircraft.
The 747-100's CWT is known to have been involved in several incidents and accidents, the most notable being the TWA Flight 800 accident on July 17, 1996. The National Transportation Safety Board (NTSB) determined that the probable cause of the accident was an explosion of the CWT, resulting from the ignition of a flammable fuel/air mixture in the tank. High temperatures in the CWT, which increased during taxiing for takeoff, led to a higher evaporation rate of the small amount of fuel at the bottom of the tank. This resulted in an increase in the flammability of the fuel vapor/air mixture within the tank.
The CWT in the 747-100 is particularly vulnerable to explosions due to its location and design. It has minimal heat rejection capabilities, which cause internal temperatures to drop slowly during flight. Additionally, the fuel tanks within the fuselage, including the CWT, are required to withstand rupture and retain fuel during emergency landings. The combination of high temperatures, fuel vapors, and minimal heat rejection makes the CWT susceptible to explosions, especially if external heat sources are present.
The 747-100's CWT is not the only fuel tank in the aircraft. There are also wing fuel tanks and aft fuel tanks, and in some variants such as the 747-400, there is a horizontal stabilizer fuel tank. The wing fuel tanks are filled first, and then any remaining fuel needed for a particular flight is placed into the CWT. This is done for structural reasons. The CWT has a large volume, with a Jet A fuel capacity of 86,363 pounds (12,890 gallons).
The 747-100's wing center section and CWT have been the subject of investigation and regulatory attention due to the TWA Flight 800 accident. The Federal Aviation Administration (FAA) and other organizations have studied and implemented measures to enhance the safety of aircraft fuel systems, particularly center wing tanks, to prevent similar incidents from occurring in the future.
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The 747-131's center wing tank exploded over the Atlantic Ocean in 1996
The Boeing 747 is a large aircraft with multiple fuel tanks in its wings. The 747-131, in particular, had a large center wing tank (CWT) with a Jet A fuel capacity of 86,363 pounds (12,890 gallons). On July 17, 1996, a 747-131 operated by Trans World Airlines (TWA) as Flight 800 exploded over the Atlantic Ocean about eight miles south of East Moriches, New York. All 230 passengers and crew on board were killed, making it the third-deadliest aviation accident in US history.
The aircraft involved in the accident, registered as N93119, had taken off from John F. Kennedy International Airport in New York City at 8:19 pm, en route to Paris, France. About 12 minutes into the flight, at an altitude of about 13,700 feet, the center wing tank exploded, leading to the crash. Investigators from the National Transportation Safety Board (NTSB) determined that the cause of the explosion was the ignition of flammable fuel/air vapors in the center wing tank.
While the exact source of ignition energy could not be determined conclusively, investigators identified a likely scenario. It was believed that a latent fault in an electronic fuel quantity indicating system component within the fuel tank, combined with a short circuit or another fault outside the tank, resulted in a high-energy electrical arc. This arc ignited the flammable vapors in the center wing tank, causing the explosion. The presence of air conditioning packs located directly below the center wing tank also contributed to the accident. The air conditioning packs transferred heat into the fuel tank, raising its temperature and increasing the flammability of the fuel vapors.
The investigation also revealed that the aircraft had been exposed to high ambient temperatures at the airport before departure, and the operation of the air conditioning packs further influenced the temperatures within the tank. Additionally, traces of explosives were found in the cabin, but these were believed to be residue from a recent explosive detection training exercise. Some witnesses reported seeing a streak of light approaching the airplane, but investigators attributed this to a stream of burning fuel leaking from the crippled aircraft after the initial explosion.
This tragic accident highlighted the potential dangers associated with the design and operation of aircraft fuel systems and led to several safety recommendations by the NTSB, particularly regarding fuel tank and wiring configurations. It also underscored the importance of comprehensive investigations to identify causal factors and implement preventive measures to enhance aviation safety.
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The 747's center wing tank is located inside the fuselage
The Boeing 747 is a widebody aircraft with a large fuel capacity. The 747's centre wing tank (CWT) is located inside the fuselage, in the centre of the plane's wing span. This central location allows for the storage of a large volume of fuel, which is essential for the aircraft's long-range capabilities.
The 747's centre wing tank is distinct from the wing fuel tanks, which are located within the wings themselves. The wing tanks take advantage of the natural shape and construction of the wings, utilising the large enclosed empty spaces to store fuel. This design not only provides additional fuel capacity but also contributes to the structural integrity of the wings by counteracting the upward bending moment caused by lift, resulting in a lighter wing structure.
The centre wing tank, being located inside the fuselage, has different structural requirements than the wing tanks. Metal fuel tanks within the fuselage must be able to withstand internal pressure and rupture forces during emergency landings. They must also manage the fuel vapor and air mixture that accumulates above the fuel surface, as this mixture can pose a potential explosion hazard if ignited by static electricity or arcing electrical components.
The centre wing tank plays a crucial role in the 747's fuel system, working in conjunction with the wing tanks and, in some variants, additional fuel tanks in the horizontal and vertical stabilisers. By distributing fuel across multiple tanks, pilots can adjust the aircraft's centre of gravity and ensure stable flight. However, the centre wing tank's location inside the fuselage has also been associated with safety concerns, as evidenced by the 1996 TWA disaster, where old wiring ignited fuel vapour inside the central tank.
In summary, the 747's centre wing tank is located inside the fuselage, contributing to the aircraft's fuel capacity and range capabilities. Its central location allows for the storage of a significant volume of fuel while also influencing the aircraft's trim and balance. However, the presence of large fuel tanks within the fuselage underscores the importance of safety measures to mitigate the risks associated with fuel vapour and potential ignition sources.
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Frequently asked questions
Yes, the 747 has always had a fuel center wing tank (CWT).
A center wing tank is located inside the fuselage. The wing skin constitutes the walls of the wing fuel tanks.
Each tank can feed fuel to its own engine, and it is possible to cross-feed fuel from any tank to any combination of engines. However, it is not possible to cross-feed tank-to-tank during the flight.
The 747's fuel tank contains a large amount of fuel, making it prone to fire and explosion hazards during operation, parking, and maintenance. The upper space of the fuel tank gathers a combustible oil and gas mixture, which is a potential safety hazard.
Early 747s had a central tank, but by the 1990s, they were barely used due to safety concerns. The latest variant, the 747-8, has reduced reliance on wing tanks compared to earlier models through a redesigned wing structure and more efficient engines.
