I travel by air with my 5lb papillon in a carry-on pet bag.  This crate (x-small size) is small enough that it can be placed inside a checked bag for use when we reach our destination.  The crate is more than enough space for her.  

For my most recent trip, I dicovered that Wayfairs had such a good price on the crate that it turned out to be less expensive to purchase the crate and have it shipped directly to my destination rather than paying the checked bag fees.

I will likely purchase this crate again next time I travel with my dog.