I was able to fit 2 of my panniers in my bike box (emptied them so it would be easier to fit all my stuff in the box), so I checked one as my "luggage", and used one as a carry on. I had to completely repack my panniers when I got to my destination though. That was coming home when I had a small bike box. Going to my destiation with a bigger bike box, I didn't need to check any bags as luggage, everything was in my bike box and my one carry on pannier full of snacks and entertainment for the plane.