Can I use the Evenflo Symphony All-in-One on an airplane, and are there any restrictions?

Yes, the seat is certified for aircraft use but only when used with the 5-point harness system — it cannot be used in booster mode on aircraft. The FAA recommends children under 9 kg (20 lbs) use a rear-facing restraint, children 9 to 18 kg (20 to 40 lbs) use a forward-facing restraint, and children over 18 kg (40 lbs) use an aircraft seat belt. (Pages 17, 63)