I've flown from the U.S. to Ireland and back in a traditional wool kilt. Leaving the U.S. the metal detectors were set high, so the buckles set it off (I'd put my belt and sporran through the x-ray) and I had to be wanded. No big deal - I wasn't in a hurry, and I expected it. On the way back the detector wasn't set as high, so I didn't set anything off, again putting the sporran and belt through the conveyor belt.

As for sitting on the pleats for five to six hours, I just spent some time after sitting arranging them under me so they were flat, and I didn't have any problems.

Andrew.