If you plan on flying with your bike often, I highly recommend investing in a good bike bag. Bike bags are better for travel than cardboard boxes because they provide more protection and the wheels make them much easier to lug around. Unless you’re doing a one-way bike trip (in which case you’ll need to discard a bike box upon landing and secure a new one before take-off), a bike bag is definitely the way to go. I have the Dakine Bike Roller Bag and I have had no issues when flying with my bikes.