How Aircraft Fueling Works: From Refinery to Runway

Jet Fuel: Chemistry and Specifications

Commercial aircraft almost universally burn Jet A-1, a highly refined kerosene-based fuel with precisely defined specifications governing its energy density, freezing point, flash point, viscosity, and dozens of other properties. Jet A-1 is the international standard; the US domestic market uses Jet A, which is virtually identical except for a slightly higher freezing point (-40°C vs. -47°C for Jet A-1). This difference is irrelevant for most operations but matters for extremely cold environments or very long high-altitude flights where fuel in the wing tanks can approach freezing.

Jet fuel energy density is one of aviation's great advantages over electric alternatives. Jet A-1 contains approximately 43 MJ/kg (megajoules per kilogram) of chemical energy, compared to the best lithium-ion batteries at around 0.9 MJ/kg — roughly 48 times less energy per unit mass. Even accounting for the 30–40% thermodynamic efficiency of a jet engine (compared to 90%+ efficiency for an electric motor), aviation fuel carries roughly 15–20 times more usable energy per kilogram than batteries. This energy density advantage means the fuel for a transatlantic flight weighs about 80 tonnes — manageable for a large aircraft — while batteries with equivalent energy would weigh over 1,200 tonnes, far exceeding any practical aircraft design. Electric flight is economically viable only for very short regional routes with small aircraft.

Fuel quality control is extreme. Every fuel delivery is tested for contamination, particularly water (which can freeze in fuel lines and stop fuel flow, or promote microbial growth), particulates (which can clog filters), and off-specification properties. Fuel samples are taken at the refinery, at the pipeline terminal, at the airport fuel farm, and again from the fueling vehicle or hydrant before it enters the aircraft. Airlines maintain their own quality control programs in addition to fuel supplier monitoring. A fuel quality incident — wrong fuel delivered, contaminated batch — is a serious safety concern that triggers immediate investigation and temporary withdrawal of the affected fuel batch from service.

Airport Fueling Infrastructure

Modern major airports use hydrant fueling systems — underground pipelines that deliver fuel from the airport's central fuel farm directly to fueling pits installed beneath each aircraft parking position on the apron. Hydrant systems eliminate the need for large fuel trucks to carry fuel to each aircraft; instead, a small hydrant servicer vehicle (essentially a pump unit with hoses) connects to the underground hydrant outlet and pumps fuel directly into the aircraft's fuel tanks. This is dramatically faster than traditional truck-based fueling for large aircraft, more environmentally safe (less fuel-handling exposure), and creates less traffic congestion on the busy apron.

The fuel farm — a complex of large storage tanks typically located at the airport perimeter — receives fuel by pipeline from the regional petroleum distribution network, or in some locations by fuel truck convoy, rail, or even barge. Major hub airports maintain days or weeks of fuel reserves to ensure supply continuity in the event of pipeline disruptions. Hartsfield-Jackson Atlanta's fuel farm has approximately 12 million gallons of storage capacity — enough for several days of normal operations. After the Colonial Pipeline cyberattack in May 2021 (which disrupted fuel supply to the US Southeast including Atlanta), the fuel reserve at ATL provided crucial time to arrange alternative supply logistics.

Fuel pricing at airports varies enormously and is a significant factor in airline economics. Into-plane fuel prices — what airlines actually pay per gallon for fuel delivered into their aircraft — can vary by 20–50% between airports, reflecting local taxes, infrastructure costs, competition between fuel suppliers, and geographic supply logistics. Airlines practice "tankering" — deliberately carrying extra fuel from cheaper airports — when the price differential exceeds the cost of hauling the additional fuel weight (which increases burn on the outbound leg). Dispatchers calculate the exact break-even point using current prices and aircraft weight-burn data, and add extra fuel up to maximum takeoff weight if economically justified.

Fueling Operations: Procedure and Safety

Fueling a commercial aircraft is a carefully sequenced procedure with multiple safety interlocks. The fueling supervisor identifies the aircraft, confirms the aircraft's fuel order from the ground handling system, and positions the fueling vehicle. Before connecting, the vehicle must be bonded (electrically connected) to the aircraft to equalize any static electricity charge that might cause a spark at the fuel connection point. Aircraft engines must be shut down or positioned such that jet blast cannot affect the fueling area; APU (Auxiliary Power Unit) use during fueling is controlled per each aircraft type's procedures.

Overwing fueling (filling tanks through open caps on the upper wing surface) is used on smaller aircraft. For large airliners, single-point pressure fueling — one connection point under the wing that can simultaneously fill all tanks through the aircraft's fuel management system — is standard. Modern aircraft fuel systems allow fueling rates of 1,500–3,000 liters per minute, enabling a Boeing 777's 181,283-liter maximum fuel load to be delivered in under 2 hours with a high-flow hydrant connection. The aircraft's fuel quantity management system monitors tank levels during fueling and sends automatic shutoff signals when target quantities are reached, with the fueling operator monitoring independently as a backup.

Fuel spills during aircraft fueling are a serious environmental and safety concern. Jet fuel is a petroleum product that can contaminate groundwater and soil, and it is flammable. Airports operate detailed spill prevention and response programs, with specialized vacuum trucks available to recover fuel quickly from apron surfaces. Aircraft mechanics and fueling supervisors are trained to recognize and immediately report any fuel leak from the aircraft's fuel system, as fuel leaks can indicate a structural problem or damaged seal that must be repaired before further flight. After major refueling events (first fueling after extended maintenance), fuel samples may be taken from the aircraft's own sump points to verify that no contamination occurred during the fueling process.

Sustainable Aviation Fuel: The Path to Net-Zero

Sustainable Aviation Fuel (SAF) is one of the most discussed topics in aviation decarbonization. SAF is a drop-in fuel — chemically similar to conventional Jet A-1, certified to the ASTM D7566 standard, and usable in existing aircraft and infrastructure without modification — that is produced from non-petroleum feedstocks. Current approved SAF feedstocks include used cooking oil, agricultural waste, municipal solid waste, forestry residues, and alcohol-to-jet pathways using agricultural sugars. SAF blended with conventional jet fuel at up to 50% blend ratio is approved for commercial use; 100% SAF certification is being pursued.

On a lifecycle basis, SAF can reduce CO2 emissions by 50–80% compared to conventional jet fuel, depending on feedstock and production pathway. This accounts for the CO2 released during burning (similar to conventional fuel) minus the CO2 absorbed by the feedstock during its growth and offset by the avoided petroleum extraction. The key qualification is "lifecycle" — production, transportation, and processing of SAF also consume energy and generate emissions that must be counted. SAF is not zero-carbon, but it is substantially lower carbon than conventional Jet A-1 on a full lifecycle basis.

The fundamental challenge with SAF is scale and cost. Total global SAF production in 2023 was approximately 300 million liters — enough to fuel roughly 0.1% of global aviation demand. The International Air Transport Association (IATA) target for net-zero aviation by 2050 requires SAF to supply about 65% of the required carbon reduction, implying production must scale by a factor of several hundred from current levels. Cost is the other barrier: SAF currently costs 3–8 times more than conventional jet fuel, depending on production pathway. Government mandates (the EU ReFuelEU mandate requiring 2% SAF blend in 2025, rising to 70% by 2050, and similar programs in the UK and US) are designed to create demand certainty that attracts capital investment in production capacity. Every major airline has now signed SAF supply agreements, and fuel suppliers are investing in production facilities — but the scale and timeline of the transition remain deeply uncertain.