I travel with four instruments (PP&M on tour): Dobro, old Martin D-28 (I don't believe in playing some junker on stage and leaving the good one at home in the case), 5-string, and mandolin. The two guitars are in (white!) Calton cases, and get checked as baggage. So far, so good, and that's about five years now. I've had to replace latches a couple of times, and four of the "protective" domes have been knocked off of the older case, but there's been no instrument damage. Al at Calton says they're looking for a better latch system that will work with their cases. The banjo and mando get carried on board - obviously the mando is no problem, and the banjo case (original hardshell) fits in the overhead of all aircraft except, surprisingly, 777. Occasionally I run into a problem on very small (prop) planes, and Continental (whom I still like) once paid a bunch of money to repair my banjo after dropping it on the tarmac. Sometimes getting both on board requires Peter to sing "Puff the Magic Dragon" to the gate agent, but mostly, just the name of the group is enough to get them to realize that we make our living on the road, and to understand that we need special consideration. Peter and Noel (Paul) both check their guitars in Calton cases - Noel's with a heavy canvas outer cover which protects the latches and domes. Dick's upright bass gets checked as excess baggage in a fiberglass case with heavy-duty latches and internal airbags.