Great-circle distance
Distance between two airports is computed with the haversine formula on a sphere of mean radius R = 6371.0088 km. That is the IUGG arithmetic mean radius derived from the WGS-84 ellipsoid, and it is the value that minimises error when a sphere is substituted for the ellipsoid.
A sphere is an approximation. Measured against WGS-84 geodesic distances across 3,989 real airport pairs, the spherical result deviated between -0.39% and +0.54%, median -0.09%. For itinerary display that is well inside any useful tolerance.
Great-circle distance is not distance flown
Aircraft do not fly the great circle. They follow airways, avoid restricted airspace and route around weather, so the distance actually flown is longer. The UK Government’s Greenhouse Gas Inventory applies an 8% uplift to great-circle distance to approximate real routing, as documented in the GOV.UK guidance Journey emissions comparisons: methodology and guidance.
A 9% figure circulates widely in secondary sources. It traces back to a different IPCC document, not the GOV.UK methodology, and it is not what we use.
Coordinates
Airport latitude and longitude come from OurAirports. Coordinates are stored to five decimal places, roughly one metre — far finer than the calculation needs, but it costs nothing to keep the source precision.
Times and dates
Times shown are the local times you entered at each airport. Each airport in the dataset carries its IANA timezone, resolved from its coordinates, so date and time handling stays correct across daylight-saving changes and the international date line. See Data sources.