I was just thinking about this last night. I have both the hard case and the soft case mentioned by LWaB. I use the soft case for local flights on small aircraft where I get to carry my bike to the plane and the pilot places it (gently) in the cargo area. Having had a couple minor damge problems with TSA re-packs with the hard cases, I can't imagine traveling on a major air carrier with the soft case.
But... I want to arrive at my destinatiuon and roll up my case, strap it to my rack and ride out of the airport. So I was thinking about some kind of homemade, multi-piece rigid insert for the soft case. And I didn't come up with a difinitive plan. Anybody got an idea?