The reason I kept my daughter RF @ 3 yrs old on our flight from NY to FL is that it decreased the worry of her bothering nearby passengers (someone is always cranky on a plane) -- she could only kick her own seat cushion.... She could also see me & do all kinds of things with her legs: cross them, hold them up straight toward the top of the plane seatback, hang them over the sides of the carseat, bend her knees up to her chin :blah blah blah: The Radian wasn't available 3 years ago, though, so I don't know how it installs on the plane.
If your toddler rides FF, then due to the lack of "wings" on the Radian, you might be able to lean over & nurse him while you're both buckled? You would have to push against the force of take-off, which might be more bothersome in a twistedly contorted position, LOL, but the risk of doing so in the plane is not like it is in a car/truck :twocents: It's never safe to lean over other occupants inside of a road vehicle.