Топливная система воздушного судна

Overview

The aircraft fuel system encompasses the complete network of tanks, booster pumps, fuel feed lines, transfer pumps, crossfeed valves, and management logic required to store jet fuel safely and deliver it reliably to the engines throughout all phases of flight. Beyond the fundamental supply function, modern fuel systems perform an active aircraft management role: by sequencing which tanks are emptied in which order, the system continuously manages the aircraft's center of gravity, maintaining it within approved limits that affect both structural loads and aerodynamic efficiency.

The total fuel capacity and its distribution across the airframe vary enormously between aircraft types, from approximately 26,000 litres in a narrowbody such as the Airbus A320-200 to over 226,000 litres in a long-range widebody such as the Boeing 747-400. Fuel is the heaviest variable payload on any commercial aircraft, and its management is accordingly a central concern for flight operations, weight and balance, and structural loading.

How It Works

Most commercial aircraft use a gravity-segregated tank layout with a centre tank and two wing tanks as the core structure, supplemented on long-range aircraft by additional trim tanks in the horizontal stabiliser or additional centre tanks in the fuselage. Engine feed is typically from the wing tanks via AC-motor booster pumps that maintain positive pressure at the engine-driven fuel pumps. If wing tank feed pressure is lost, crossfeed valves allow any tank to supply any engine.

Transfer sequencing prioritises drawing fuel from the centre tank first (on most aircraft), which removes weight from the fuselage and reduces wing root bending moment — the dominant structural load on swept wings in flight. As the centre tank empties, the system transitions to wing tank feed. On aircraft with horizontal stabiliser trim tanks, fuel is transferred aft during cruise to move the centre of gravity rearward, reducing the aerodynamic download on the horizontal tail and thereby reducing trim drag and fuel burn. The Airbus A320 family uses trim tank transfer in this manner to achieve a measurable fuel efficiency benefit.

Key Components

• Wing Tanks: Sealed structural bays within the wing box, forming the primary fuel reservoir. Typically divided into inner (inboard) and outer (outboard) cells with transfer valves between them.
• Centre Tank: Located in the wing centre section under the fuselage floor. Large capacity; fed to engines first during normal fuel sequencing.
• Boost Pumps: AC motor-driven centrifugal pumps (two per tank as standard) that pressurise fuel for delivery to the engine fuel metering units. Prevent engine-driven pump cavitation at altitude.
• Fuel Quantity Indicating System (FQIS): Capacitance probes in each tank section measure fuel volume and temperature; fuel management computers convert this to fuel mass accounting for density variation with temperature.
• Crossfeed Valves: Motor-operated valves that interconnect the port and starboard fuel manifolds, enabling any tank to supply any engine.
• Refuelling Panel: Single-point pressure refuelling connection (usually under the wing leading edge) allowing rapid ground refuelling with automated cutoff at preset quantities per tank.
• Vent System: NACA-inlet vent scoops and internal vent galleries maintain tank internal pressure near ambient, preventing structural damage from differential pressure during climb and descent.

Aircraft Applications

• Boeing 737-800 — centre tank plus two wing main tanks; gravity crossfeed capability; total ~26,000 litres
• Airbus A320-200 — centre tank plus two wing tanks plus trim tank option; FQMS manages transfer automatically
• Boeing 777-300ER — three-tank system (centre plus two wings) with optional auxiliary centre tanks; total ~181,000 litres
• Boeing 787-9 — centre tank plus wing tanks; no bleed-powered fuel pressurisation; electric boost pumps only
• Boeing 747-400 — five main tanks plus horizontal stabiliser trim tank; total ~226,000 litres; complex multi-pump sequencing

Advantages and Limitations

Modern fuel management systems are highly automated, reducing the manual workload of fuel transfer management that once required frequent crew attention on older aircraft. The ability to actively manage center of gravity through fuel sequencing provides a meaningful fuel efficiency benefit, particularly on aircraft with trim tanks. The structural integration of fuel within the wing provides thermal mass that moderates skin temperature fluctuations and serves as a heat sink for hydraulic and electrical systems on some aircraft types.

Fuel system complexity scales dramatically with aircraft range and size. Long-range widebodies require sophisticated leak detection, inerting systems, multiple independent pump circuits, and comprehensive quantity indication across dozens of tank sections. Fuel quantity sensing errors have historically contributed to accidents, driving requirements for multiple independent measuring systems with cross-comparison. Fuel contamination — by water, microbial growth, or incorrect fuel type — remains an ongoing maintenance concern requiring regular tank sampling and draining.