Again, those recommendations/requirements for for cars and based on car collisions. The seat itself and how your child sits in it will be exactly the same whether it is forward or rear facing. The difference would be how forces are distributed in the event of a crash.
On a plane the only thing you're likely to encounter would be some turbulence, and forward/rear facing isn't going to make any difference in terms of safety. Having them in the seat will definitely be safer than in your arms under any circumstances. It will also be more comfortable for the child and yourself.