Air Force and Coast Guard aircraft will fly “intercept and identification” exercises over Washington tonight as part of efforts to prevent suicide aircraft attacks or other threats to the capital, a military spokesman said.

The latest exercise of what the North American Aerospace Defense Command calls “Falcon Virgo” involves Civil Air Patrol Cessna-182 light aircraft and a Coast Guard HH-65 Dolphin helicopter between 11:30 p.m. Monday and 5:30 a.m. Tuesday, NORAD said in a statement.

Airspace over the nation’s capital is tightly controlled and aircraft that stray into restricted airspace near the White House, Capitol, and national monuments risk being shot down by military aircraft.

During the September 11 terrorist attacks against the Pentagon and attempted strike on either the White House or Congress using hijacked airliners, U.S. military jets had to be scrambled from southern Virginia.

Since those attacks, the U.S. military has set up a defense system to better protect the region from such threats.