Since the good old days of flying with your bike never existed, we pine for the possibility that such days might exist in the future, a day so good, we will be able to take our bike unwrapped to the plane and the baggage handlers will take care of it with no extra fees. Until then, we're using hard cases; if the bike has an integrated seat mast, we'll probably be taking the Tri All 3 Sports Velo Safe Pro Series ISP.
ISP is not Internet Service Provider; it is Integrated Seat Post. The case is taller and narrower than Tri All 3's regular Velo Safe. It still fits within the airlines "oversized" regulation of 160 total inches (that is adding length, width, and height together), but is tall enough that you have 32in between the furthest edge of the big chain ring to the top of the mast. In many cases, you'll even be able to leave your saddle in place.
The exterior dimensions are 51 inches long by 16 inches wide by 38 inches high (51 L x16 W x 38 H). Those dimensions include the two-inch casters that the case rolls on. The inside dimensions are 47 inches long by 13 inches wide by 32 inches high (47 L x 13 W x 32 H). With these dimensions, the typical bike owner will take off the wheels and secure the fork and chainstays to the base with a mount for the fork, Velcro straps for the stays, and a foam block for the bottom bracket. It is a good idea to purchase bubble wrap or foam rubber pipe insulation and use this to protect the frame tubes. Then, they'll remove the bars, and use a strap to secure the bars to the top tube or down tube. Next, the wheels will be secured to either side of the frame. Pedals can be left on. Depending on the total height of the saddle and clamp on top of the mast, the saddle might be able to stay in place as well.