The term “Additional Center Tank” in aviation refers to an auxiliary fuel tank installed in the center wing box area of certain aircraft to increase fuel capacity for extended range or longer endurance flights. Often abbreviated as ACT, this system plays a key role in long-haul operations by enabling the aircraft to carry significantly more fuel without compromising the normal payload. This article will explore what Additional Center Tank is, its functions, and its relevance in aviation fuel management and aircraft design.
Understanding the Role of Additional Center Tank in Aviation
The Additional Center Tank (ACT) is an auxiliary fuel tank installed between the main wing fuel tanks or within the center wing box structure of some commercial and military aircraft. Unlike the primary fuel tanks, which are integral parts of the wings and fuselage, the ACT is a supplementary system designed to hold extra fuel. This helps the aircraft achieve longer distances without refueling, thus expanding its operational range considerably.
The ACT is widely used in aircraft models such as the Boeing 747 and 777 series, where the structural design supports the inclusion of a center tank to hold additional kerosene-based jet fuel (Jet A or Jet A-1). For example, the Boeing 747-400 has a center fuel tank capacity of approximately 6,154 US gallons (23,300 liters), which significantly boosts its total fuel endurance. The installation of an Additional Center Tank can increase an aircraft’s flight time by several hours depending on consumption rates and payload.
The Technical Features of Additional Center Tank
An Additional Center Tank is engineered for optimal weight distribution and fuel management within the aircraft. It typically consists of sealed metallic or composite fuel cells with integrated fuel pumps and valves to transfer fuel to the main engines. The fuel quantity in the ACT is monitored through sensors interfaced with the aircraft’s electronic fuel quantity indication system (EFQIS), which provides real-time data to the flight deck.
In terms of capacity, the ACT often holds between 5,000 to 8,000 gallons of fuel depending on the aircraft model and design specifications. The fuel from the ACT is transferred to the main wing tanks first or directly to the engines as needed. This system ensures that the center of gravity remains stable during flight as the fuel is consumed, maintaining safe flight characteristics. The incorporation of an ACT requires additional maintenance checks and safety protocols, especially because center wing tanks have been scrutinized following incidents related to fuel vapor explosions.
Safety and Operational Considerations of Additional Center Tank
Safety is a paramount factor when dealing with an Additional Center Tank in aviation. The aircraft’s fuel system is designed to prevent the risk of fire or explosion inside the center wing tank. Technologies such as nitrogen inerting systems are used in modern aircraft to replace oxygen in the tank ullage with inert nitrogen gas, reducing flammable vapors during flight. The Federal Aviation Administration (FAA) requires stringent certification tests to ensure that the Additional Center Tank complies with all safety standards.
Operationally, the use of an ACT affects aircraft loading, pre-flight fuel calculations, and emergency procedures. Flight crews must carefully manage fuel transfer from the Additional Center Tank during all phases of flight, especially during takeoff and landing, to maintain safe balance and meet certification criteria. As the ACT is often located in the center wing box—between the main landing gear—it has implications on landing gear design and wing structural integrity, requiring robust engineering solutions.
For more detailed technical specifications and safety standards related to aviation fuel tanks, including Additional Center Tanks, the FAA’s official documentation provides comprehensive guidelines and certification protocols [FAA Fuel Tank Safety](https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/fuel_tank_safety_overview.pdf).
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