Single-edged fixed blades may be. No other apparent limitation. Manufacturers and sellers are not exempt. Children under 18 may purchase the above weapons with written parental permission. You're in a hurry and the guards are not so they can confiscate the knife, turn you away, have you questioned, arrest you, make you check it in your baggage, require it be kept in a pouch with the pilot, or do whatever they like.
Official rules are hard to find.