10K kg
 

Question (only just relevant here!)…

Nav fees start once MAUW exceeds 2 tonne, are there any other weight points at which the calculation changes? Ie flat $50/tonne until 50 tonnes, then $100/tonne - or whatever?

Or it's standard, free to 2T, then XX/tonne from then on all they way up?

Cheers, Sam.

Pursuant to the limitation that it only applies to countries having made an agreement with Eurocontrol for collecting en-route charges (all European countries, I presume), the calculation formula can be found here:
​​​​​​https://www.eurocontrol.int/sites/de...of-payment.pdf

And the administrative context is described here:
https://www.eurocontrol.int/articles...-route-charges

In short, the factor that brings in the weight of the plane is:
p = 0 , if the MTOW of the aircraft is less than 2 metric tons,
p = square root of (MTOW/50) , with MTOW measured in metric tons, in all other standard cases

So it is neither a linear nor a step up factor.
For an aircraft whose MTOW is exactly 2 tons, the factor p = 0.2
12.5 tons, p = 0.5
50 tons, p = 1
200 tons, p = 2

If we are talking about Eurocontrol - the square root of weight is used in the calculation. So the charges go down (per ton) as the weight goes up. Currently, IFR is free for those under 2T but every state is free to make their own rules about local charges and they set their own unit rate.