Any time that we have brought a car seat, we have used it on the plane, not so much I am concerned about the safety on the plane, but rather I do not want to check a car seat. Once a car seat has been tossed around, it's integrity could have changed totally and is no longer safe for use. This is the reason why insurance companies will replace car seats that have been in accidents regardless if there is any visible damage to the car seat (at least that is the case in Canada). If we are not able to use it on the plane, I just don't bother bringing one.
For the person that is using Happy Limo, I wish that I brought my own car seat, their car seats are terrible. And they expect you to install it yourself, with no manuals/instructions.