No, he shouldn't have any problems with his costume for the event at all in my opinion since it's part of his costume. For the plane I would place it in the checked baggage so they do not throw a hissy fit about it.
My son was a pirate(as was the rest of the world) for the 9/22 party and we packed the sword in the checked luggage. We had no problems with it at the park.
Have a great time!
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