This is the link to TSA suggestions on 'flying with instruments';
http://www.tsa.gov/traveler-information ... nstruments
This is a recent article from Taylor Guitar referring same;
http://www.taylorguitars.com/blog/guita ... dium=email
I can't speak of other cases, but the one I have includes a "PEV" - "Pressure Equalization Valve". Probably a marketing gizmo but....