Airlines begin using a Computer Assisted Passenger Prescreening System to separate passengers who require additional scrutiny ("selectees"), based on behavioral characteristics and a government watch list of known or suspected terrorists.
Nineteen Al Qaeda terrorists hijack four U.S. airliners and crash two into New York's World Trade Center towers and one into the Pentagon; the fourth crashes in Pennsylvania. Thousands die in the deadliest terrorist attack on U.S. soil.
On a Paris-to-Miami flight on American Airlines, Richard Reid tries to ignite explosives in his shoes; he is overpowered.
The Aviation and Transportation Security Act gives the federal government direct responsibility for airport screening. The Transportation Security Administration is formed to oversee security for all modes of travel.
The government orders random inspections of passenger shoes and limits carry-on bags to one bag plus one personal item per passenger. It mandates reinforced cockpit doors on U.S. passenger planes.
The government begins banning certain dangerous items, such as scissors, knives and box cutters, from carry-on bags.
A gunman opens fire at an El Al ticket counter at LAX, killing two people before he is shot to death by a security guard.
The government begins requiring passengers to display valid government ID. It restricts access beyond airport checkpoints.
A federal program is created to arm and train pilots to defend against hijackings and other violence.
By year's end, TSA is screening all checked bags for explosives, prohibited items and other dangerous materials at all U.S. airports. Bags are subject to hand searches.
The TSA abandons plans to test a new Computer Assisted Passenger Prescreening System (CAPPS II) for millions of passengers to detect potential terrorists and begins testing a Registered Traveler program, in which frequent travelers who submit to pre-screening and fingerprinting are allowed to use faster security lines.
British officials foil a plot to blow up aircraft using liquid explosives in carry-on bags, on flights from Britain to the U.S.
All liquids, gels and aerosols are banned from carry-ons; the ban is later eased to allow travel-sized toiletries of 3 ounces or less. TSA loosens its ban on certain sharp objects.
TSA announces it will train more than 500 "behavior detection officers" to scan passengers for suspicious behaviors.
TSA launches the Registered Traveler pilot program.