Quite large multinational, European HQ. Any training related travel is Y, regardless of length/destination. Otherwise, anything over four hours is C, and those four hours include layovers. So I have been in (intra-EU) C several times because total flight time was above four hours, but had to endure Y to the US because I was going there for a course. Guess which flight was more expensive...
Good thing is we can choose whichever airline and flight combinations we want - but have to give explanations if chosen option is not the cheapest - and also are able to extend duration of the stay or add a stopover if we want to do sightseeing or side-trips.