Current airport security procedures, which require a valid boarding pass, federal screening, and attention to carry-on contents, have evolved over decades. These layers of security were often implemented following attacks or foiled plots that exposed vulnerabilities in aviation safety.
The bombing of Pan Am Flight 103 over Lockerbie, Scotland, on December 21, 1988, which killed 270 people, led to major changes. The FAA mandated X-ray or manual inspection of all checked luggage at European and Middle Eastern airports, along with extra random searches and verification that checked bags belonged to boarded passengers.
Following the September 11, 2001, attacks, further security measures were introduced. The attempted detonation of explosives hidden in footwear by Richard Reid in December 2001 led to the eventual compulsory removal of shoes at checkpoints. New restrictions on liquids and gels were implemented in 2006 after a plot to detonate liquid explosives on transatlantic flights was uncovered. This resulted in the "3-1-1" policy for carry-on liquids.
A Christmas Day plot in 2009, involving explosives concealed in a passenger's underwear, prompted the accelerated deployment of full-body scanners in major airports. These scanners use radio waves to detect a range of banned objects. Security measures continue to evolve, with the TSA expanding facial recognition technology and new aircraft featuring retractable security gates for cockpits.