Question Britax Advocate 65 CS in an airplane seat?

Hi, planning on flying in a few months with our daughter who'll be 21 mo. We have an Advocate 65 CS and are not sure if it'll fit in an economy airline seat. The FAA has a brochure recommending a carseat no wider than 17", and our Advocate probably measures around 21" (based on googling, haven't been out to measure her tonight). Wondering if anyone's flown with this seat and had any trouble either fitting the bottom, or the side impact cushions into an aircraft seat.

Any info'd be much appreciated.

I am not sure how the new Britax seat designs compare, but the older (non-Advocate) convertibles fit OK in airline seats because they sat up higher on a narrower base and the wider part of the seat shell would clear the armrests. I am not so sure as far as the Advocate goes, though, because those SIP cushions might take up too much room to comfortably sit next to. Many airlines require the car seat to be installed next to the window and I am not sure about clearance against the wall. In a center row you can often intsall anywhere but again, the person sitting next to the seat might be left with too little room. I traveled with a classic Marathon and while it was a bit of a squeeze leaving the armrest down it still fit; it did, however, take up the entire back of the airline seat. I could dig up the plane types if needed.

If you are looking to get a great travel seat that is light and easy to lug along, as well as inexpensive, I would look at the Cosco Scenera.

You can see both the classic MA and the Scenera in action, as it were, in my trip "review" here, also includes the CARES and how we lugged the seats through the airport:
http://www.car-seat.org/showthread.php?t=102030

Thanks so much, we'll definitely have a look at the Scenera for this trip. I like the sound of a lightweight seat. We're also thinking Radian, but it's a toss-up between super heavy, expensive and will last us longer as her second seat, or lighter, more affordable, not as long lasting. I also worry that the Radian will have to be installed FF on the 'plane and besides the fact that I'd like her RF, it looks so upright, I think she may be uncomfortable if she sleeps. I see that you installed the Scenera RF for the flight...was the install fairly easy? Would we likely have to bring along a towel or pool noodle segment?

Thanks again,
Kate