Sorry if this is well-tread ground. We are traveling by air this summer. DD (almost 4) has her own seat on the plane. Is it preferable to bring the carseat onto the plane and fasten it into her seat, or gate check it? I'm guessing the former, in which case my question is, will a Britax Marathon actually fit in a standard plane seat, and, how much of a hassle is it to install?
Yes, if she has her own seat I would do your best to put her carseat in there.
The Marathon should fit. It is rated for airlines, so you should be fine. IF it doesn't fit, then you can gate check it.
This thread might be helpful to you.
At that age, CARES is a lot more comfortable for everyone. Marathons fit pretty poorly in most planes.
I've flown numerous times with boulevards (same footprint as a marathon) and it fits fine. I do lift the armrest, and ask for a belt extender (because otherwise the buckle ends up at an impossible spot)
I have a CARES and a marathon. I thought the marathon was more comfortable for my daughter and less hassle for me. Even though she fits the guidelines, the CARES always seems too big. And then right when it seems to start being the correct size, they outgrow it (or my son did, anyway.)
I didn't use a seatbelt extender on the marathon and I couldn't get the seat out at the end of the flight. The airline maintenance crew couldn't get it uninstalled either. They ended up disassembling the airplane seat! So, yes, I am a proponent of the seatbelt extender.