This calculation is an estimate (and not an exact figure) based on the criteria established by Ademe, taking into account the following parameters
the distance between the departure airport and the arrival airport
the presence or not of a stopover
a percentage increase (approximately 5%) added to the great circle distance, also called the “orthodromic distance”
a fixed quantity of kerosene required for take-off and landing
passenger class
From this data, a number is obtained corresponding to the amount of CO₂ emitted per flight, scaled to a passenger.