If you’re in the Washington area Tuesday morning and hear low-flying helicopters or planes overhead, don’t be alarmed: It’s an exercise.

The North American Aerospace Defense Command, also known as NORAD, will conduct a national-level test between 10 and 11:30 a.m. to practice intercept and identification procedures, a public information officer said.

The officer, Capt. Jennifer Stadnyk, said the exercise is scheduled for Tuesday morning but could be delayed or canceled because of weather.

Low-flying helicopters could be heard or seen in close proximity to military or military-contracted aircraft in or around Washington, a press release said. Helicopters and planes are also scheduled to fly in the area of Frederick, Md., and the Charlottesville and Mechanicsville areas of Virginia. The planes “will be taking on the role of aircraft of interest,” NORAD said.

NORAD has conducted exercise flights like this throughout the nation and Canada as part of its response to the Sept. 11, 2001, attacks. A regional NORAD exercise, called Falcon Virgo, took place after midnight Tuesday, Stadnyk said.