How does fuel weight affect aircraft weight and balance?

Fuel increases aircraft weight and changes centre of gravity according to each tank’s position. As fuel burns, total weight falls, but the CG can move forward, aft or sideways; it does not automatically become safer. Accurate loading therefore uses fuel mass, tank-specific moments, burn sequence and checks at take-off and landing.

In our Aviation & Real-World Flying coverage, we treat fuel as two related loading inputs: its weight contributes to total aircraft weight, while its location contributes to the moments that determine centre of gravity. Flight simulators use the same principle, although simplified aircraft may not model individual tank arms, transfer systems or changing fuel moments accurately.

How is fuel included in aircraft weight?

Usable fuel is added to the aircraft’s empty or operating weight and remains part of gross weight until it is consumed, drained or jettisoned. Where fuel quantity is known by volume, calculate its mass using fuel mass = volume × density.

Litres, US gallons and Imperial gallons are volume units. Kilograms and pounds are the loading units normally used for weight-and-balance work. Our explanation of why aviation fuel is loaded by weight rather than gallons alone covers the practical reason for that distinction.

Contingency, diversion, alternate and final-reserve fuel do not disappear from the landing calculation. If they are expected to remain aboard, they remain part of landing weight and CG.

At a given flight phase, carrying more fuel normally means a higher stall speed, longer take-off or landing distance and poorer climb performance than the same aircraft at a lower weight. The performance figures and legal limits must come from the applicable aircraft manual or operator data.

How does temperature affect fuel weight?

Temperature changes fuel density and volume, but it does not change the mass of a fixed quantity of fuel. For the same measured volume, warmer fuel is less dense and therefore weighs less; for the same mass, warmer fuel occupies more space.

• Fixed mass: if an aircraft contains 15,000 kg of fuel and none is used, leaked or spilled, warming it does not turn it into fewer kilograms.
• Fixed volume: 1,000 litres of warm Jet A or Jet A-1 normally has less mass than 1,000 litres of the same fuel at a colder temperature.
• Completely filled tank: fuel expands as it warms. Because aircraft tanks are vented, overfilling can lead to fuel being expelled through the vent system; that lost fuel does reduce the mass aboard.

This is the point that often causes doubt: yes, temperature matters when converting volume to fuel weight, but not because existing fuel mass simply vanishes as it warms. Use the approved density, temperature correction or dispatch value for the fuel being loaded. A generic Jet A or aviation-gasoline approximation is suitable only for rough planning.

Which fuel is used to compute empty weight and its corresponding CG?

The amount of fuel used when computing aircraft empty weight and its corresponding CG is normally unusable fuel. Usable trip and reserve fuel are then added as separate loading items.

Check the exact definition attached to the aircraft’s empty-weight record. Standard empty weight, basic empty weight, licensed empty weight and operating empty weight are not interchangeable terms, and the treatment of equipment, crew and operating fluids can differ. Likewise, zero-fuel weight excludes usable fuel but includes payload, so it is not simply another name for empty weight.

How does fuel move an aircraft’s centre of gravity?

Fuel moves the CG because every tank has an arm, or distance from the aircraft datum. Its contribution is calculated using moment = fuel weight × arm, followed by CG = total moment ÷ total weight.

For the complete arithmetic, including datum, arms and signed moments, use our worked method for aircraft weight-and-balance calculations.

A tank’s effective arm can change as its level falls because fuel tanks are not perfect rectangular containers. If the aircraft supplies fuel-moment, index or loading tables for different quantities, use those values instead of multiplying the entire tank by one assumed arm.

What does 15,000 kg of fuel do to CG?

The quantity alone cannot show the direction of CG movement; the tank arm is also required. Assume an aircraft without usable fuel weighs 45,000 kg at an arm of 15.00 m, then receives 15,000 kg of fuel at 16.00 m. Its new CG is ((45,000 × 15.00) + (15,000 × 16.00)) ÷ 60,000 = 15.25 m.

Put the same 15,000 kg at an arm of 14.00 m and the resulting CG becomes 14.75 m. The airplane fuel weight is identical in both cases, but one load moves the CG aft and the other moves it forward.

Can excess fuel cause an aft CG?

Yes, excess fuel can produce an aft-CG condition when enough of it is stored behind the aircraft’s existing CG. Extra fuel in a forward tank has the opposite effect, while fuel close to the CG may add substantial weight with little longitudinal movement.

An indication such as excess fuel with an aft CG therefore describes two limits that must be checked separately. The aircraft may be overweight, outside the aft CG boundary, or both. Removing fuel from an aft tank could move the CG forward, but it is acceptable only when fuel requirements, tank-loading restrictions and approved procedures still permit that change.

Adding forward fuel may shift a loaded CG into the envelope, but it cannot correct a maximum zero-fuel-weight exceedance and may create an overweight condition. Repositioning or removing passengers, baggage or cargo is often the proper correction.

Does burning fuel always improve weight and balance?

No. Burning fuel always reduces gross weight, but it can move the CG towards either limit depending on the tank being used.

An aircraft can be inside its take-off envelope and outside, or much closer to, its landing limit after fuel burn. The permitted CG envelope can also change with aircraft weight. Multi-tank aircraft therefore use prescribed feed and transfer sequences to control CG, maintain engine supply and respect structural restrictions.

Fuel burn does not reduce zero-fuel weight because passengers, baggage and cargo remain aboard. Planning to burn fuel after departure cannot make an overweight or out-of-envelope take-off legal.

How is fuel imbalance different from an aft or forward CG?

A fuel imbalance normally refers to unequal quantities in the left and right tanks, creating a lateral rolling moment towards the heavier wing. Forward and aft CG describe longitudinal balance along the fuselage.

Opening a crossfeed valve does not necessarily pump fuel directly from one wing to the other. On many aircraft, crossfeed lets one or both engines consume fuel from the fuller side while pumps or selectors prevent use from the lighter side. The approved checklist specifies the permitted configuration and maximum imbalance.

During which phase of flight can Boeing 777 fuel balancing be carried out?

Boeing 777 fuel balancing may be carried out during any phase of flight under the applicable balancing procedure. This is the standard answer to the B777 fuel-balancing question; the phase of flight itself is not the stated restriction.

That does not make improvised pump or crossfeed selections acceptable. Crews must use the checklist for the exact 777 variant and operator, observe fuel-system messages and restore the normal configuration when balanced. In a simulator, follow the modelled checklist because some 777 add-ons simplify or omit pumps, crossfeed logic and imbalance alerts.

How should fuel be entered in a weight-and-balance calculation?

Fuel should be entered by tank, in the correct mass units, and checked at every relevant flight phase.

1. Confirm the empty-weight record. Use the weight, moment or CG for the actual aircraft and installed equipment. Verify whether unusable fuel is already included.
2. Determine required block fuel. Account for start, taxi, trip, contingency, diversion or alternate fuel and the required reserve without treating the reserve as planned burn.
3. Split fuel between tanks. Follow tank-capacity, loading-order and minimum-fuel rules rather than dividing the total arbitrarily.
4. Convert volume correctly. Use the right gallon type, fuel density and temperature basis. Keep kilograms and pounds separate throughout the calculation.
5. Apply each tank’s loading data. Use its arm, moment or index table rather than one generic fuel station.
6. Check the whole flight. Verify ramp, take-off and landing weight, CG, maximum zero-fuel weight, tank limits and lateral imbalance. Check intermediate points when a transfer or burn sequence could create the most adverse CG.

What changes when calculating fuel for a Piper Seminole?

A Piper PA-44 Seminole must be calculated from the weight-and-balance data for its exact model and airframe, not from a generic light-twin example. Its recorded empty weight and moment reflect the equipment installed in that particular aircraft.

The Seminole normally uses aviation gasoline, so a Jet A density must not be used for volume conversion. Enter the usable left and right fuel quantities using the applicable Pilot’s Operating Handbook loading data, and confirm how unusable fuel is represented. Capacities and loading information can differ between PA-44 variants, so an unverified capacity copied from another Seminole is not a safe substitute.

How should fuel be set in a flight simulator?

Set simulator fuel by individual tank wherever the aircraft exposes those controls, then verify total weight and CG on the aircraft’s loading page, electronic flight bag or simulator weight-and-balance display.

• Choose one loading interface. A complex add-on may overwrite fuel entered through the simulator’s general menu, while a simpler aircraft may rely entirely on that menu.
• Check the units. A value intended as kilograms can produce a serious error if the field expects pounds, gallons or a percentage.
• Inspect every tank. A 50% slider may fill every defined tank halfway, including centre, auxiliary or trim tanks that the planned load should leave empty.
• Allow for loading order. Some aircraft require wing tanks to reach a specified quantity before centre or auxiliary tanks are loaded.
• Verify after applying the load. Confirm fuel quantity, gross weight and CG again after closing the loading page or starting the flight.
• Model the landing condition. Remove only the predicted trip burn, following the expected tank sequence, and leave planned reserve fuel aboard.

Our version-agnostic guide to setting fuel by tank and verifying payload in a flight simulator covers the practical loading workflow.

What causes incorrect fuel weight or balance results?

What should be changed if the aircraft is outside limits?

The correction must match the failed limit; reducing total fuel is not a universal solution.

• Above maximum weight: remove payload or non-required fuel while preserving all mandatory fuel and operational margins.
• Forward or aft CG: reposition or remove passengers, baggage or cargo. Alter fuel distribution only where the aircraft’s loading instructions permit it.
• Left-right fuel imbalance: correct quantities on the ground or follow the aircraft-specific in-flight balancing checklist.
• Above maximum zero-fuel weight: remove payload. Adding fuel or planning to burn fuel cannot correct this limit.
• Simulator-only anomaly: check units, per-tank quantities, empty-weight configuration and whether a custom aircraft loader has replaced the simulator’s values.