You may notice some noise overhead this weekend. That's because of a joint-military operation with Canada, designed to protect from another 9-11 attack.

Friday begins a four-night exercise by NORAD, the North American Aerospace Defense Command.

Their mission is called "Exercise Falcon Virgo." It's part of "Operation Noble Eagle," which started as a response to the September 11 attacks.

NORAD is using three kinds of aircraft: the Air Force C-21, the Civil Air Patrol C-182 and the Coast Guard's M-H-65 Dolphin helicopter.

You may see these flights in unusual places because they are testing NORAD's ability to coordinate with all the area flight controllers and identify and intercept aircraft.

These flights will run from about midnight to 5:30 a.m., from Friday early Monday morning.

The military has responded to 5,000 possible air threats in the US since 9-11.