A.V.
We were not allowed to use our own seat on international flights. Your mileage may vary on domestic flights. I would not plan on it being allowed and get a CARES harness (wish I knew about that). Ours was also approved by the manufacturer but that didn't mean the airline had to allow it. Call them, and be prepared to check it because sometimes customer service doesn't know what's really allowed/available. We were told we could borrow one of their seats, but there were only 2 per plane and we never got one.