http://www.chron.com/disp/story.mpl/metropolitan/6653799.html#

The North American defense operation known as NORAD — once known mostly as a chief component of ballistic missile defense — will be conducting exercises over South Texas skies today reflective of its new responsibility to protect American and Canadian skies from potential terrorists.

A NORAD spokesman urged people not to worry if they see a pair of fighter jets flying at low altitudes close to a civilian plane. It's just an interception test.

“You may see two F-16s off the wings of a civilian aircraft,” said spokesman Lt. Desmond James. “Potentially this could be concerning to people on the ground. If they see or hear this going on, don't be alarmed. You don't have to call 911.”

After the Sept. 11 attacks, NORAD's mission changed to include the interception of unidentified civilian aircraft in the U.S. and Canada.

An unidentified aircraft could be a drug transporter, a terrorist, an inexperienced pilot who wanders into restricted airspace or, in rare cases, a plane whose radio equipment has become inoperable or its pilot incapacitated.

NORAD, which stands for North American Aerospace Defense Command, conducts tests monthly in Washington, D.C., James said. It also does exercises in other locations in the two countries.

“Post 9/11, NORAD can look not only outside of the U.S. and Canada but inside,” James said. “If there is an aircraft flying and not talking to FAA or aircraft administration, NORAD may become involved, including launching fighters to go up and visually see what this aircraft is.”

A week ago, NORAD F-16s were dispatched to inspect an uncommunicative aircraft near Muncie, Ind. The pilot was unresponsive when the military pilots arrived. They followed the aircraft until it crashed in a rural area of Randolph County, Ind.