The North American Aerospace Defense Command is conducting calibration flights over the Washington area early Tuesday morning.
The flights will take place from about 2 a.m. to 6 a.m. and will involve a Beechcraft King Air aircraft flying patterns at 1,000 to 16,000 feet above ground level. The flights will test and calibrate systems and equipment. If the exercise is canceled for any reason, it will be rescheduled for early Wednesday or Thursday.
Read more: http://www.norad.mil/News/2012/030512.html