How the calculations are checked

A calculator that renders correctly and returns a plausible number can still be wrong. These are the steps each of the 30 calculators goes through before it is published.

Built from a published formula

Each calculation starts from a primary source: the ICAO Standard Atmosphere for anything involving pressure, density or temperature aloft; the FAA handbooks for navigation and performance technique; NASA Glenn for compressible flow and the speed of sound; and the standard spherical trigonometry for great-circle work. The sources used are listed at the bottom of each calculator page so you can check the working yourself.

No calculation here was produced by copying another website. Where a competitor site and a primary source disagree, the primary source wins.

Three checks for every calculation

Each calculator has to pass all three before it goes live.

1. A worked reference example. A case with a known published answer is run through the calculator and the result has to match. That example is shown on the page, along with an independent check of the figure using different arithmetic.
2. A boundary or error case. Inputs that should fail have to fail cleanly. A crosswind stronger than the aircraft true airspeed, a dew point above the temperature, a reserve larger than the fuel on board: each returns a plain explanation rather than a number that looks fine.
3. A unit switch. The same calculation is run in different units and the answers have to agree once converted. This catches conversion errors, which are the commonest bug in calculators of this kind.

These checks are automated tests that run against the calculation code, not a manual pass over the finished pages. The worked example printed on each page is the same data the test uses, so the page and the test cannot drift apart.

Exact models rather than rules of thumb

Several of these calculations have a familiar cockpit shortcut: 1,000 ft per inch of mercury for pressure altitude, 120 ft per degree for density altitude, 2 percent per 1,000 ft for true airspeed. Those shortcuts are good enough for mental arithmetic and they are why pilots can do this in their heads.

This site uses the full model instead, then tells you what the shortcut would have given and how far apart they are. For density altitude at a hot, high airfield the difference is a few hundred feet. For true airspeed at 10,000 ft it is about 6 kt. Knowing the size of that gap is more useful than picking one method and staying quiet about the other.

Stated assumptions

Where a result rests on an assumption that is frequently untrue, the page says so next to the result rather than in small print at the bottom. Still air in a glide calculation, dry air in a density altitude calculation, and a steady wind across a whole leg are all examples.

What is deliberately absent

There is no takeoff or landing performance, no weight and balance approval, no aircraft limitation checking and no go or no go indicator anywhere on the site. Those need aircraft specific approved data and validation well beyond what a general purpose calculator can offer. A calculator that gave a verdict on them would be more dangerous than useful.

Reporting an error

If a result looks wrong, please say so. Include the calculator name, the exact inputs, the answer you got and the answer you expected. That is enough to reproduce it immediately. The contact page has the address.