Extra fuel has a transport cost

When can cheaper departure fuel cost more overall?

Carrying fuel consumes fuel and can displace payload.

Price the delivered fuel

Suppose each 1 kg loaded for tankering causes 0.05 kg additional burn before arrival. Only 0.95 kg remains to replace a destination uplift. Cost per deliveredkg is departure price/0.95, before other costs. Comparing departure and destination price without the transport penalty overstates the saving.

The penalty depends on aircraft, route, mass and conditions. Use the appropriate supplied graph or approved planning system; a constant fraction is a synthetic teaching model. For larger loads, the burn penalty can change with the very mass being added.

Check feasibility before profit

Tank capacity, ramp mass, take-off mass, landing mass,CG and performance can cap the additional fuel. A cheap uplift that exceeds a landing mass limit is not a feasible saving. Payload displacement can also outweigh a fuel-price advantage when the flight is otherwise mass limited.

Operational factors can favour tankering for reasons other than price, such as uncertain fuel availability, but they do not remove the associated constraints. The plan should state the purpose and the governing limits rather than treating every low-price uplift as automatically desirable.

Solve the inverse quantity

To deliver D kilograms at destination with fractional burn penaltyp, load D/(1−p). Additional transport burn is that load minus D. At D = 1,000 kg andp = 0.05, load 1,052.63 kg and burn 52.63 kg. This is different from merely adding 5% to 1,000, which would deliver 997.5 kg.

The laboratory compares delivered-unit cost and a stated mass allowance. It omits changing performance, taxes, contracts and commercial payload value. Use it to understand the break-even relationship and inverse calculation, then apply the actual flight and commercial data for a decision.

The financial break-even point and the maximum permitted load answer separate questions and must both be satisfied.

Why can a fuel-plan update change the traffic allowance?

Fuel and traffic share several mass limits while fuel burn changes the arrival state.

Intersect the allowances

For each proposed extra-fuel load, recompute take-off and landing fuel and the traffic allowance at zero-fuel, take-off and landing limits. The limiting phase can change. A take-off allowance may improve after a runway change while a landing limit still prevents carrying the desired tankered fuel.

In the synthetic case,DOM40 t, take-off limit 64 t and take-off fuel 10 t allow 14 t traffic on that constraint. Adding 2 t take-off fuel reduces this allowance to 12 t. If the added fuel remains to landing, the landing allowance also falls by 2 t; if some burns, its effect is smaller there.

Account for carried-fuel burn

The extra burn caused by carrying extra mass means loading one extra kilogram does not necessarily add one kilogram to arrival fuel. A planning system may iterate mass, trip fuel and landing mass to a consistent solution. Treat the resulting fuel and mass values as a connected version of the plan.

Do not reuse an earlier trip burn after a substantial mass or route change unless the supplied method explicitly allows it. Equally, do not invent a generic percentage correction when actual aircraft data are available. The laboratory uses a stated linear penalty only to expose the feedback.

Explain the active constraint

If the desired tankering exceeds the smallest remaining allowance, the proposed extra load is infeasible under those facts. Options may include reducing tankering, changing payload or revising the operation through the authorised process. A financial saving cannot override a structural or performance restriction.

The useful answer states three things: the maximum feasible extra load, the mass phase that limits it and the expected delivered quantity after the supplied penalty. This makes the trade-off reviewable and prevents a large fuel-price saving from hiding an unacceptable loading condition.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.