Armed F-16s from the Wisconsin Air National Guard were on the runway and could have shot down the errant Northwest flight if the order had come, 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, from San Diego to Minneapolis, might have been hijacked after its pilots failed to respond to radio transmissions for more than an hour. NORAD ordered at least two planes scrambled at the guard facility in Madison, Wisconsin.
The NORAD spokesman said the F-16s, normally armed with 500 rounds of air cannon bullets and six air-to-air missiles, were on the runway when the alert was canceled once the pilots finally made contact with FAA controllers.
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 the Minneapolis Center.
The concern grew as the pilots ignored a command from the Minneapolis approach controllers to begin a descent for landing.
The National Counterterrorism Center in Washington was notified, and authorities began to scrutinize the passenger list, according to Pierre Thomas and Jason Ryan of ABC News.
Once contact was re-established, after an hour and 18 minutes of silence, the controllers ordered the pilots to carry out a series of zigzag maneuvers in order to prove "the pilots had command and control of the craft," according to people briefed on the incident.
For some controllers, the incident was an eerie and painful reminder of the controller at the Cleveland Center who unsuccessfully attempted to contact United Airlines Flight 93 on September 11, 2001.
"United 93, United 93," the controllers called out repeatedly until another aircraft reported seeking smoke on the ground. The plane crashed in a Pennsylvania field as passengers attempted to storm the cockpit.
In the case this week of Northwest 188, controllers tried used a variety of FAA frequencies, the Northwest private frequency and texting services to contact the plane as it sailed through the air at 37,000 feet.
The pilots finally responded when they were contacted by the Denver controllers—-an indication they had not changed frequencies on their radios when they passed into the Minneapolis air space.
According to people briefed on the incident, the pilots had to be asked three separate times if they were okay and had control of the plane.
The pilots said they had a "cockpit distraction" and were having a "heated discussion" about a "company issue," according to a person briefed on the conversation with the controllers.
The incident prompted widespread speculation that the pilots had fallen asleep although controllers reported "no indication" that the pilots were "groggy" once they began to respond to the radio calls.