Maedze: That is why we have a CARES harness. You attach it to the plane seat and it makes a 4 point harness, much safer than just a lapbelt. That would have been my 1st preference to use on the plane.
Thanks guys, I will bring the Radian. I will have to practice collapsing it and such, what a pain ;) I will put it in the travel bag I have for it to carry it over my shoulder, while I am wearing DD and pulling my carryon (sounds like fun times!).
What shocks me more is that my sister said my nephew weighs a little under 13kg. The referenced booster they use is for kids weighing 15kg or more. I don't understand how people can be so casual about car seat safety when this is statistically the most likely bad thing to happen to you?