Can I use this car seat in booster mode on an airplane?
No, this restraint cannot be used in booster mode in aircraft. It can only be used with a 5-point harness in aircraft. In booster mode, this restraint is not certified for aircraft use because a belt-positioning booster requires the use of a lap/shoulder belt system, which is not available in aircraft. (Page 17)
From the official Evenflo Symphony All In One Car Seat manual, page 17
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