Armed F-16s from the Wisconsin Air National Guard were on the runway and could have shot down the errant Northwest flight, officials said today. "As a force of last resort, NORAD is always prepared to do whatever is necessary," NORAD spokesperson Mike Kucharek told ABCNews.com. Air traffic controllers feared Northwest Flight 188, might have been hijacked after its pilots failed to respond to radio transmissions for more than an hour. Air traffic controllers reported the pilots initially failed to respond to commands as it passed from the air space controlled by the FAA Denver Center into the area controlled by...