To error on the safe side. I remove my converter from my FP I carry on the plane and put a sealed cartridge in the body. This way I can pierce it when I land and be ready to write. In my luggage I put my bottle ink in a tupperware container then in a plastic bag. I had an ink bottle leak in my luggage before, not pretty.
I've managed to travel with a FP with no leaks before - I think it depends largely on how much ink is in the cartridge.. if there's only a tiny air bubble, there's not much air to expand and push out ink.. if it's 50% air, then it will expand a lot and make a huge mess..