I haven't tried flying in the US in a kilt (not yet anyway)

But haven't encountered any problems on UK internal flights - I have more problems with my hand luggage because being diabetic I need to carry needles (never had a problem with them in the US though!). Cardiff and Edinburgh always insist on examining my hand luggage which I have never encountered at any other airports.

Flying to Edinburgh next week but that's only an hour but I have no problem getting seated - I just run my hands over the pleats before I sit down and it works fine.

ALways pack the sgian and kilt pins in hold luggage and put sporran and belt through the hand luggage machine before going through the portal.

Edinburgh Airport even let my mate through with his kilt pin as he had forgotten to put it in his luggage and I thought it would be confiscated and lost for ever. I would suspect that this is the exception to the rule though and wouldn't risk it.