The plot to bring liquid explosives onto flights from London to the U.S. and Canada in 2006 prompted the Transportation Security Administration to institute a limitation of 3 ounces on all liquid and gel containers placed in carry-on bags.
This led to the now well-known and much maligned 3-1-1 rule for carry-on bags: 3-ounce containers inserted into a 1-quart bag for each passenger. The 3-1-1 rule has endured for 17 years. Since that time, airport security has moved forward strategically and technologically. The most significant strategic change has been the introduction of PreCheck in 2011, the risk-based system that makes travelers better known to the TSA, giving them access to expedited screening lanes at airport security checkpoints.
Currently, the TSA is deploying computed tomography (CT) screening devices for carry-on bags, which provide a more precise, 3D view of bags’ contents.
