Since hardening cockpit doors and taking other measures after the 9/11 al Qaeda attacks, the U.S. aviation security focus has shifted primarily from hijackings to plastic and other explosives that can be carried aboard a plane or hidden in baggage.
The United States has particularly been focused on efforts by al Qaeda in the Arabian Peninsula to develop undetectable explosives since the unsuccessful attempt by the so-called “underwear bomber” to bring down a Delta Air Lines jet over Detroit in 2009.
Article Appeared @http://ktla.com/2014/07/02/tsa-to-heighten-airline-security-on-us-bound-flights-before-holiday-weekend/