Can I use this car seat on an airplane, and are there any restrictions?

When used with the internal harness and properly installed, this restraint is certified for use in aircraft. However, in booster mode (without the internal harness), this restraint is NOT certified for aircraft use because a belt-positioning booster requires a lap/shoulder belt system, which is not available in aircraft. You should check with your airline before departure to confirm the restraint meets their requirements. (Page 19)