It's necessary medical equipment -- you could copy off the information regarding that from the Federal Transportation website -- there's usually a link to that on all airline sites. Maybe plaster the vest bag with brightly colored medical equipment stickers of some sort. I also seem to recall someone on this site indicating that the vest shouldn't be put in the cargo area due to variations in temperature. Maybe drop an email to Hill-Rom and see if they have any suggestions, or give them a call. They might even be able to get you a wheeled bag -- they sent ours to us overnight after our orginal one ripped.
The irony is that Northwest Airlines gave a talk about traveling with CF at the U of MN education day a few years ago -- suggested a certain size and type of carry-on bag with wheels, info on traveling with equipment, meds...
A couple months later a friend of mine, who'd attended the conference, took a family vacation to Cancun. She decided to call ahead and was on the phone for hours... She just decided to take it as a carry-on. I think she did get some grief from one individual, but was able to take it onto the plane and I do know she's travelled on the same airline since then and hasn't had any issues.
