The cause of the alarm was attributed to a flock of birds, or another glitch on the Doppler radar, rather than an actual small aircraft. Helicopters were sent to up confirm that there was no threat. According to White House spokespeople, there have been several other false alarms since 9/11, but what they aren't saying is that it is likely that a more sensitive radar system has been installed in the D.C. area to detect low-flying aircraft to direct a much-upgraded air defense system. Protective measures include F-16 fighter aircraft on strip alert at Andrews Air Force Base, helicopters, and surface-to-air missiles in fixed and mobile locations around the region.
Several hundred violations of the DC no-fly zone occur each year, most of them by disoriented private pilots in small aircraft. To warn off planes that stray into D.C. no-fly space, NORAD has developed the "Visual Warning System" (VWS). Pilots that stray into the Washington Metropolitan Area Air Defense Identification Zone that can't be reached by radio will be "lit up" with a flashing sequence of red/red/green eye-safe laser light. An FAA Special Advisory tells pilots that see the lasers to immediately exit the zone and to radio air traffic control. The "notice to airmen" warning states that non-compliance to procedure could result interception by military aircraft and the use of force.
VWS has seven turrets around the region, and are directly remotely by NORAD. The 1.5-watt red and green lasers are diffused through lenses to produce a wide low-intensity beam about 100 feet in diameter (when they are 18.5 kilometers from the turret). The lasers should be visible at distances up to 18.5 kilometers during the day and up to 46 kilometers at night.
The laser system is not effective during poor weather conditions such as rain or overcast skies, but any small aircraft pilot flying in such conditions is likely to pay more attention both to his navigational instruments and the radio. It is unknown what effect the lasers will have on a flock of birds. Doug Mohney
On April 27, 2005 -- shortly after a new high-tech laser warning system was turned on in Washington D.C., to warn away private pilots who cross into the "No Fly" zones around the Capital, White House, and other key buildings in the area -- the President of the United States was rushed into an underground bunker at the White House due to a false alarm from that system. The Vice President was also moved to a "secure location" under heavy armed guard. Reporters were not alerted or moved.