We just used our CARES with our 3.5 yo DEN-MCI on a Bombadier with leather (pleather?) seats and he was very uncomfortable. He kept sliding down in the seat so the chest harness rode very high on his chest/neck. I tried to show him how to sit cross legged and not slip, but he was not very comfortable. I had read reviews on Amazon where parents brought a square of non-slip rug backing to prevent slippage, but I wasn't expecting non-cloth seats in coach.

On the return he told me he didn't want the harness, so we tried to just use the seatbelt, which of course he could easily undo. He also slipped on the seats with just the seatbelt.

I told DH that for as convenient as it was to check the carseats, we really need to bring them on in the future - the kids (we also have an almost 2 year old who won't be a lap infant any more) are much more comfortable in them and the carseats have an expectation of "sit still, stay strapped in." Plus they can see out the window better and I think the familiar carseat is more comfortable for them to sleep in.

Search Traveling Toddler Accessory on Amazon for a cool little strap that attaches the carseat to a rollaboard - you can then use it as a stroller!