I flew from Seattle to DC last winter, with no security problems. In fact, it was a whole lot easier just taking the sporran off and laying on the belt rather than emptying out all my pockets, then trying to stuff it all back on the other side. The only disadvantage was I was in an 8 yard heavy wool kilt and had the exit seat. Crawling over two other people trying to keep the pleats in line was difficult. Other than that, most people didn't even notice (although the good looking ticket agent in DC really took a liking to it).