After the Sept. 11 attacks, Congress ordered the federal government to take over the screening duties and set a deadline of Nov. 19, 2002 for workers to be in place at 424 commercial airports.
Airports were given until Dec. 31, 2002 to have machines in place to check all bags for explosives, but the Homeland Security Act extended the deadline by one year.
Metal detectors are set on the highest levels.
All carry-on bags may be subject to individual hand searches after screening.