Every operator has a cost per hour in their head. Almost none can say what went into it. And that is the difference between a number that guides a decision — selling, switching models, accepting a charter, planning the downtime — and a number that is only good for arguing with your partner.
The problem is not math. Any spreadsheet can divide expenses by hours flown. The problem is what goes into the numerator and the denominator, and most cost-per-hour figures out there are born from six silent mistakes. When building the cost-by-model view inside Alis, this set of rules is what separated the reliable number from the guess with two decimal places.
1. Only realized cost counts
The first source of an inflated cost is the quote. A requested quotation, an approved estimate, an authorized service — none of that is cost. It's pipeline. Cost is what was performed and paid: the completed work order item, the part actually bought and installed, the invoiced third-party service.
And there is a trap inside the work order itself: the cover and the parts rarely agree. The total on the order header is typed in by someone; the sum of the items, parts and third parties is what actually happened. When they diverge — and they diverge more than you'd think — the sum of the parts wins. A cover with no parts at all is a suspect, not a source.
2. Dollars aren't converted by guesswork
Aviation parts arrive priced in dollars. Adding R$ to US$ gives a number that doesn't exist; converting at today's exchange rate invents a cost the operation didn't pay. The honest rule is simple and a bit uncomfortable: what was bought in dollars stays in dollars, in its own column, with the exchange rate of the purchase day when one was recorded — and with no rate, the amount comes out in USD, labeled.
A cost per hour that mixes the currencies looks more complete. It is less true.
3. Fuel burn only with a unit
Here physics comes in. A Cirrus SR22 is fueled in gallons; a turbine helicopter, in liters or kilograms. Now imagine two fuel entries with no unit: "20 per hour" and "139 per hour". If you convert both as liters, the SR22 becomes an airplane flying on a motorcycle's tank. If you convert both as gallons, the helicopter ends up burning fuel like a jet.
A number with no unit contradicts physics — and guessing the unit from the model is making up data. The rule: liters per hour only enter the calculation when the entry states which unit it was made in. The rest stays out, and the dashboard says it stayed out.
4. Distance only when plausible
Cost per kilometer depends on distance, and typed-in distance misleads: odometer entered in the miles field, a local leg with no distinct origin and destination, a value with one zero too many. The filter that works is the speed envelope: distance divided by flight time has to fall within a range the aircraft can actually fly. Outside it, the distance doesn't count — and cost per kilometer comes only from the legs that passed the test.
5. Monthly rate only with a window
"Cost per month" for an aircraft with three weeks of data isn't a rate, it's noise. Hangar, insurance and subscriptions only become a monthly cost with a minimum observation window — and a long hangar stay can't be spread as if it were a running expense. Without a window, the dashboard shows the total and stays silent about the "per month". Staying silent is more honest than rounding.
6. Model by the RAB
It seems like a detail, and it breaks any comparison: "Cessna 550", "CESSNA AIRCRAFT 550" and "Cessna 550 Bravo" typed by three customers become three models in a spreadsheet — and the third isn't even the same airplane. The source of the model has to be the Brazilian Aeronautical Registry (RAB), not free-form entry. That is how a base with hundreds of aircraft can answer "how much does an hour of a 550 cost" without adding up different things.
The example, with demonstration numbers
To make it concrete — with illustrative values, from a fictional aircraft — here is how the rules change the result for an SR22 in one month:
| Entry | Counts toward cost? | Why |
|---|---|---|
| Fuel · 42 gal, unit stated | Yes | Unit present: converts to liters |
| Fuel · "18 per hour", no unit | No | With no unit there is no way to convert |
| Approved inspection estimate · R$ 12,400 | No | Pipeline, not cost |
| Executed work order items · R$ 9,700 | Yes | Realized |
| Imported part · US$ 1,180, no exchange rate | Separate | Stays in USD, labeled |
| Hangar · 3 weeks of data | Total, no "per month" | Insufficient window |
Demonstration values, fictional aircraft. The SR22 appears as an example of a model fueled in gallons, not as a cost reference.
The cost per hour that comes out of this is lower than the spreadsheet would say — and it's the only one that supports a decision. Anyone who has measured the cost of a grounded aircraft knows: an inflated number hides exactly the part of the operation that most needs to be seen.
Where Alis comes in
In Alis, the expense is born tied to the flight: fuel, hangar, fees and per diems are entered on the leg where they happened, and the real cost per hour of each aircraft comes out of the operation — not from an end-of-month spreadsheet. The six rules above are the ones the calculation applies, and the dashboard says what was left out and why, instead of filling the gap with an estimate.
The comparative view by model, aggregated and anonymized across operators, is what we are building on top of this base — with the same rules, because comparison between models is only worth anything if each number was determined the same way.
Want to know the real cost per hour of your aircraft? Talk to Alis — if your flights are already on the platform, the math is already done.
This article is informational. The values shown are demonstration values and do not represent real costs of any model, manufacturer or operator. Operation and maintenance decisions must rely on the aircraft's technical documentation and the applicable technical responsibility.