Commercial airplanes store most of their fuel inside the wings. The wing structure itself doubles as a fuel container, with sealed compartments between the upper and lower wing surfaces holding thousands of gallons of jet fuel. Some aircraft also carry fuel in the fuselage and in the horizontal stabilizer at the tail, but the wings are always the primary storage location.
Why the Wings Hold the Fuel
Storing fuel in the wings isn’t just convenient. It solves a fundamental engineering problem. During flight, aerodynamic lift pushes the wings upward while the weight of the fuselage pulls down, creating enormous bending stress at the point where the wings meet the body. Filling the wings with fuel counteracts that upward force, reducing stress on the wing root and allowing lighter structural designs overall. As fuel burns off during a flight, the wings get lighter gradually, which keeps the load balanced throughout the journey.
Wings also offer a large, naturally enclosed volume. The space between the front spar, rear spar, upper skin, and lower skin forms a box-like cavity that runs most of the wingspan. Engineers seal that cavity and turn it directly into a fuel tank, rather than wasting the space and adding separate containers.
Three Types of Aircraft Fuel Tanks
Not every airplane stores fuel the same way. Three designs dominate aviation, each with trade-offs in durability, weight, and maintenance.
Integral Tanks (Wet Wings)
Most large commercial jets use integral fuel tanks, often called “wet wings.” The wing structure itself is the tank. Sealant is applied along every rivet, seam, and joint so the wing skin, spars, and ribs form a fuel-tight container with no separate vessel inside. This is the lightest option since the structure serves double duty, but the sealing process is labor-intensive, and the constant flexing of the wing during flight can eventually crack the sealant and cause leaks that need resealing.
Bladder Tanks
Bladder tanks are flexible, nylon-reinforced rubber bags shaped to fit inside the wing cavity. Because the bladder holds the fuel, the wing structure doesn’t need to be fuel-tight, which simplifies manufacturing. Modern bladders use a double-wall design with a reinforced outer shell and a pure rubber inner liner. The downside is that rubber degrades over time. The most common failure is hardening and cracking of the upper surface, and a bladder that isn’t properly secured can rub against internal wing components until it wears through. Military aircraft and many smaller general aviation planes use this approach.
Rigid Removable Tanks
Some smaller aircraft use drop-in aluminum tanks that sit inside the wing and are held in place by straps. Because these tanks don’t carry any of the wing’s flight loads, they’re free from the flexing that plagues wet wings. The result is an extremely reliable system, though the added weight of a separate metal container makes this approach less practical for large airliners where every pound matters.
Fuel Storage Beyond the Wings
On wide-body aircraft like the Airbus A380, fuel isn’t limited to the wings. The A380 has eleven fuel tanks total: five in each wing and one in the horizontal stabilizer at the tail. That tail tank is called the trim tank, and it serves a specific aerodynamic purpose. By pumping fuel between the wings and the tail during flight, the aircraft shifts its center of gravity forward or backward. This reduces the amount of work the control surfaces need to do to keep the plane balanced, which lowers drag and improves fuel efficiency.
Some long-range aircraft also carry fuel in tanks within the center fuselage section, between and below the wings. These center tanks feed fuel to the wing tanks or directly to the engines, extending the airplane’s range beyond what the wing tanks alone could support.
How Fuel Gets From Tanks to Engines
Fuel doesn’t flow to the engines by gravity alone. Each tank contains electric boost pumps that pressurize the fuel and push it through a network of pipes to the engines. Large jets have multiple pumps per tank for redundancy, so a single pump failure doesn’t cut off fuel supply. A fuel selector or control valve lets pilots choose which tanks feed which engines.
Cross-feed valves add another layer of flexibility. These allow fuel from a tank on one side of the airplane to feed an engine on the opposite side. If an engine shuts down or a tank develops a problem, cross-feeding keeps the remaining engines supplied and prevents the airplane from becoming lopsided as one wing burns fuel faster than the other. On twin-engine general aviation planes, cross-feed can work by routing fuel directly from one wing tank to the opposite engine, or by transferring fuel between wing tanks first.
Keeping Tanks Safe Under Pressure
As an airplane climbs and the outside air pressure drops, the air space above the fuel inside the tanks expands. Without a way to release that pressure, the tank walls could rupture. Conversely, during descent, outside pressure rises and could crush the tank inward if a vacuum formed. Every fuel tank connects to a venting system that equalizes pressure with the outside atmosphere.
This system typically includes surge tanks at the wingtips and ventilation lines running from the fuel tanks to those surge tanks. Float valves inside the tanks ensure that at least one vent port stays clear of liquid fuel regardless of the airplane’s attitude, whether it’s climbing, descending, or banking. Engineers size these vent passages to handle the maximum airflow caused by altitude changes and fuel consumption, keeping the pressure difference within what the tank structure can safely handle.
Lightning and Fire Protection
Storing tens of thousands of pounds of fuel in the wings raises obvious concerns about lightning strikes. Commercial aircraft are struck by lightning roughly once or twice per year on average, so fuel tank protection isn’t optional. Federal regulations require that the entire fuel system prevent catastrophic fuel vapor ignition from direct lightning strikes, swept strokes across the aircraft surface, and electrical surges conducted through wiring.
Engineers achieve this through careful material choices, bonding and grounding of every metallic component to prevent sparks, and shielding of electrical wiring that runs near fuel tanks. These protective design features are classified as critical and come with mandatory inspection intervals, testing procedures, and replacement schedules to ensure they remain effective over the life of the aircraft.
Dumping Fuel in Emergencies
If a plane needs to make an emergency landing shortly after takeoff, it may be too heavy to land safely. Some aircraft solve this with a fuel jettison system that can dump fuel overboard through nozzles near the wingtips. Federal rules require that if such a system is installed, it must be able to jettison enough fuel within 15 minutes to bring the airplane’s weight down to a safe landing level.
Not every airplane has this capability. Aircraft that can meet safe climb and landing performance requirements at their maximum takeoff weight don’t need a jettison system at all. Many narrow-body jets like the Boeing 737 fall into this category. For planes that do have the system, built-in safeguards prevent the crew from accidentally dumping below a minimum reserve, enough for a climb to 10,000 feet plus 45 minutes of cruise. The jettison valve can be closed at any point during the operation, and the system is designed so that no single malfunction can cause fuel to dump unevenly from one side.