THe only way to be sure is if you have a booster seat with a 5 points harness, and there is a sticker on the side which states that your seat is FAA approved. MOST booster seats even with the 5 points harness are not FAA approved. If your booster seat has arm rests, or cup holders attached, your seat most likely is not FAA approved. I did a lot of research when looking for a seat for my DS 2, since he had outgrown his traditional car seat. I found that there are very few booster seats that are FAA approved, and those with the arm rests or cup holders usually aren't. I think it has to do with the width of the seat, not being able to fit in a regular airplane seat. My DD whose almost 5 doesn't fly with a car seat anymore, since she's in a belt positioning booster now. She does just fine with the lap belt.