The military will begin using strategically located lasers this week to warn pilots who make unauthorized flights into restricted airspace surrounding the District.
Use of the lasers comes a week after a wayward Pennsylvania pilot drifted into restricted airspace, prompting the evacuation of thousands of people from the White House, Capitol and House and Senate office buildings.
"We can't be 100 percent sure this will prevent it from happening again. But as soon as someone penetrates the [restricted zone], we will beam them," said Air Force Col. Ed Daniel, vice commander of Norad, the North American Aerospace Defense Command.
Defense Department researchers began developing the ground-based laser system two years ago.
From an altitude of 1,500 feet in a Coast Guard helicopter, a laser looks like a high-powered traffic light. It isn't visible until the military turns one on, but then it is easily seen unless thick clouds obscure the beams. Once it's on, a laser blinks rapidly three times -- red, red and green -- pauses and blinks again.
As Coast Guard Lt. Shane Hill pilots a Sikorsky Jayhawk helicopter over Southeast Washington, a single laser that appears to be just south of the Washington Monument is pointed at him and begins blinking.
"They're tracking us right now. No other aircraft can see that. It's very directional," Lt. Hill said.
A beam 5 miles in length is merely 100 feet wide, so it hits its target and avoids disrupting other aircraft, said Randy G. Walden, technical director of the Air Force Rapid Capabilities Office.
The lasers are weak enough so they won't harm a pilot's eyes, but strong enough so the beams can be seen up to 25 miles away at night.
At an undisclosed center within the District, military officials monitor the capital region airspace and can turn on and aim a specific laser with a click of a mouse and notify pilots when they fly into a 2,000-square mile restricted zone known as the air defense identification zone.
The airspace isn't off-limits, but pilots must obtain a code from the Federal Aviation Administration so the agency can track their plane, and they must maintain radio contact with air-traffic controllers.
Private pilots, military and law-enforcement aircraft have violated the restricted airspace 1,716 times since that creation of the air defense identification zone in February 2003, FAA spokeswoman Laura Brown said.
The Air Force won't disclose how many lasers it has deployed, but they are scattered around the perimeter of the air defense identification zone and within the area.
The zone covers a region from the Baltimore-Washington International Airport to Washington Dulles International Airport to Ronald Reagan Washington National Airport.
Each laser cost $500,000, Col. Daniel said. Lasers also are equipped with cameras strong enough to identify a plane in good conditions.
There are no plans to deploy the warning system in other cities.
The federal government began a campaign last month to warn pilots about the new system.
"These are unlike any lights pilots have ever seen," FAA program manager for special operations Rick D. Hostetler said.
Use of the lasers won't change the military's rules of engagement, Col. Daniel said. Those rules allow the military to shoot down a plane.
But the lasers could make it likely that military pilots must scramble less often like they did last week when a Cessna flew within three miles of the White House.
"We are still going to scramble airplanes if we have to," Col. Daniel said.