But such a decision would not be a spur of the moment decision while the aircraft is in flight and would not therefore provide an explanation as to why the aircraft would have had to turn back from Belarus. A flight plan would have been submitted and the relevant authorizations sought before the flight left Paris. If they were not, that would look like something that would not amount to an ext.circ. OTOH, if they were and Russia suddenly decided to refuse entry/revoke an authorization for no clear reason, that would be more likely to be an ext. circ.