I have traveled on a Lot (Polish air) with my cat when moving continents, but only took her out of the carrier because the plane was no more than 1/3 full and I asked permission first. The stewardesses allowed everyone to reseat as they pleased.
There are few alternatives for household pets, as most cargo ships don’t allow pets, and Amtrak only allows a certain distance before disembarking (and trains don’t cross oceans).
