1. The invoice never left the paper age
Fuel is 25–30% of an airline's operating cost, and roughly 40% of aviation supplier invoices still arrive as PDF or paper. Procurement has been automated; settlement has not. The result is a document arriving from a supplier at a station, priced against a contract negotiated somewhere else, for a service that an operational record somewhere else again can confirm or contradict.
Errors in direct operating cost run at about 1% of spend. On a multi-billion-dollar fuel bill that is a large number, spread thin across tens of thousands of lines a year — which is exactly the shape of exposure that survives because no single line is worth a finance team's attention.
2. The error is on the supplier's own paper
What makes this different from a modelling exercise is that the finding does not depend on anyone believing our estimate. A duplicate charge is visible on the supplier's own invoice. A cancelled rotation has an operational record that says so. A tariff that expired still being applied is a date on a contract.
That evidentiary property is what lets a recovery survive contact with the supplier's finance team. A number the client believes in but the supplier can wave away is worth nothing; a number the supplier credits is the only output that counts.
3. Nobody is paid to read
Three parties could look and none of them does. The airline's own finance function is built around materiality, and a line is below it by construction. The supplier has no incentive to find its own billing errors. An ERP vendor sells the system of record, not the reconciliation of what came out of it.
That leaves the gap between what was contracted and what was invoiced, unattended by everyone whose job it is not. A contingency practice closes it precisely because it does not need a budget line to start: it is paid from what it finds.
4. Method, in outline
An engagement takes two inputs — the invoice and the contract — and tests one against the other, line by line, for the carrier, station and service date that applied. Where the operational record can confirm or contradict the charge, it is brought in. What cannot be evidenced is not claimed.
How the testing is organised, which classes of discrepancy exist, and what the evidence standard is for each — that is the engine, and it is not published here. It is available to a client in the course of an engagement.
5. Why contingency is the right shape
A fixed-fee audit is priced for the risk of finding nothing, so it overcharges the client whose books are clean and undercharges the one whose are not. A contingency aligns the fee with the outcome and removes the client's downside entirely: there is nothing to pay for looking, and nothing to pay for a finding the supplier rejects.