Yes... I think technically the Kiddy Guardian Pro 2 is allowed for flight. It has a TUV sticker on it, and there's an online manual explaining how to fit.

But, the FAA rules show two boosters - one with restraint straps and one without. Mine is neither - it doesn't have restraint straps, but rather a booster. Unless this type of seat gets more popular in the US, its un likely to change the rule book to clearly show either way...

I ended up buying a used Britax Eclipse for £20... not ideal as its our 4th car seat, but I am 100% certain it will fit and that the US Airways flight attendents will allow it... Have printed the FAA guidelines & TUV Certificate info...