Thank you so much for your answer my lord
!
I knew this topic would be a headache but as we say, "no pain no gain"..
Well basically after some researches i realized as you said that there isn't a unique way to proceed, and that OVF & landing permits vary from the operations type and all variant you mentioned.
I would like to concentrate my memoire only on private and non-scheduled commercial flights operated with biz jets.
According to what i've found here and there, for private flight, that's not a big deal, as you "only" need to comply with Entry requirements of the overflown country or the country you want to land at and wait for CAA overview and answer.
However, for non schedule commercial flights i would say it's the same as above, e.g complying with entry requirements.. but i was wondering if the fact that a bilateral agreement had been signed between the country of registration and the country you fly to would that change the deal and make things easier?
To my knowledge bilateral agreement deals with flight frequencies, designated operators, prices... But is there, a part from multilateral agreement (opensky EU/US and other?) agreement allowing any movement and/operator to perform flights between 2 different countries?
I'm not sure to be clear.. if not tell me I'll try to explain me differently
Thanks again Dallas
