As others have noted, your carseat serves a very different purpose in an airplane than in a car. The reason you rear-face in a car is to protect against head/neck and chest compression injuries in a sudden stop. I think (could be wrong, but it seems unlikely) that a plane is never going to have the type of sudden stop that can cause the G-forces that a car could. The main purpose of the car seat on a plane is to protect against bounces in turbulence, and in that case I don't see how it could matter which direction it faces.

We still rear face in the car, but I have no problem front facing on a plane, in part because there's no way our daughter's monstrous car seat could fit rear-facing without limiting recline of the seat in front of us. Also, in flight entertainment!