A new laser warning system is coming into operation in Washington to prevent planes straying into the restricted air space over the US capital.
The security alert on 11 May sparked panic
It comes less than two weeks after a disorientated private plane pilot sparked a panicked evacuation of the US Capitol area.
The new system shines red and green laser beams into pilots' cockpits.
Pilots have dropped initial complaints that the system might harm eyesight or be abused by terrorists.
The new visual warning system, or VWS, will shine a combination of different-coloured, low-level laser beams into the cockpit as a sign that the plane needs to change course.
Laser beams are fired into the pilots' cockpits
The US Air Force describes it as a simple and safe system.
Federal officials also say it is far cheaper than the $50,000 it can cost to scramble a fighter to deal with intruders.
Hundreds of planes have strayed into the 25km (15 mile) radius Flight Restricted Zone around the Washington Monument since the 11 September terror attacks.
There is also a far wider, 3,000 sq km Air Defence Identification Zone around Washington's airports that bans private planes without special transponder codes.
Pilots' groups initially believed the laser beams might affect vision and be used by pranksters or even terrorists.
But the Aircraft Owners and Pilots Association that represents more than 400,000 private pilots has now endorsed the idea.
The system is aimed at preventing incidents such as the intrusion by a private Cessna plane within three miles of the White House on 11 May.
Vice-President Dick Cheney and First Lady Laura Bush were rushed from the White House and staff in the Treasury and the Supreme Court were moved to safety.