I have a 2 year old daughter who has been flying with me since she was only 2. Her Britax car seat is approved for aircraft and we bought her a set of Child Ear Defenders at Transair, so off we went. We've never looked back.
I fly a Baron 58, so that we've found the most convenient place for her is forward facing in the rear compartment.
Drop me a line if you want more details.
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2Donkeys