Dodging a bullet....
I'm just picking up bits and pieces of the huge sweeps the FBI and other agencies are doing in this country, but I get the impression that a number of people have been located who were on planes with knives and box cutters, but were stranded in airports or dropped off at intermediate stops when the FAA suddenly cleared the skies.
I don't know exactly who made the incredibly difficult and expensive decision to ground all aircraft in the U.S. immediately, but I predict that when all the facts are known in a few weeks or months it will be discovered that this move saved countless lives.