I use a box that new bikes come in, from the bike shop. I've heard of these big airline boxes, but never been able to confirm their existence in advance, so making a trip to the airport and hoping to find one in the time before my flight departs is too sketchy a proposition for me.

I had a non-existent-big-box experience at Greyhound once, I think that put me off it. I like to pack the bike in advance.

Come to think of it, all my US tours I have not used a bike to get home - I rode home or got a car ride. My overseas tours, one time I saved the box from the flight in at a hostel, the other time I got a box from a bike shop, a friend helped me pick it up & get it to the airport.