1. Calculation of en route service units
1.1.The en route service units shall be calculated as the product of the distance factor and the weight factor for the flight concerned. The total en route service units shall consist of the total service units in respect of IFR flights, as well as the service units in respect of VFR flights, where VFR flights are not exempted in accordance with Article 31(3), 31(4) and 31(5).
1.2.The distance factor in respect of a given charging zone shall be obtained by dividing by one hundred the number of kilometres flown in the great circle distance between the aerodrome of departure within, or the entry point into, the charging zone and the aerodrome of arrival within, or the exit point from, the charging zone, according to the actual route flown as recorded by the Network Manager.
The distance to be taken into account shall be reduced by 20 kilometres for each take-off from and for each landing in the charging zone.
1.3.The weight factor, expressed as a figure taken to two decimal places, shall be the square root of the quotient obtained by dividing by fifty the number of metric tons expressed as a figure taken to one decimal in the certificated maximum take-off weight of the aircraft as shown in the Aircraft Flight Manual.
1.4.Where an aircraft has multiple certificated maximum take-off weights, the highest one shall be used.
1.5.Aircraft operators shall declare the composition of their fleet and the certificated maximum take-off weight of each of their aircraft to the body responsible for the collection of the charge whenever there is a modification and at least annually.
Where the weight factor is unknown, the weight factor shall be calculated by taking the weight of the heaviest aircraft of the same type known to exist.