Under current FAA regs you are allowed a knife with an unserrated blade of up to 4". You are supposed to be able to carry this even after inspection/search. I think that rule might change now, but I doubt it will have a real impact. I know there are people who carry knives and flashlights aboard for emergencies and personal defense once they land. These are usually people who practice fighting with and without weapons. It seemed a bit paranoid to me, but it's hard not to speculate about whether the events of yesterday would have been changed if there had been some of these types aboard. Perhaps not, but I wonder if there was ever a point aboard the airliners yesterday where a few people skilled in hand to weapon fighting could have made a stand and taken out the terrorists. Perhaps this is indelicate to talk about, but I think the Israelis do after bitter experience. I've also heard there's always an armed good guy aboard every El Al flight, but I don't know whether this is true.