The lack of instances in which terrorists try to use knives to take over a plane underscores that their tactics have shift to using explosive devices instead, which what TSA is devoting its energies to finding, Pistole said. He noted that the proposed policy would mostly conform U.S. regulations with international standards, which were changed in 2010 to allow these types of small knives to be carried by passengers. Yet none has been used in a terrorist incident so far, he said.Even though the agency is focused on new threats, "it doesn't mean old threats don't still exist," Swalwell responded. Pistole acknowledged that the knives could be used to injure people on a plane, but he said that's not the TSA's responsibility. "It really comes down to the mission of TSA," he said. "Is it to prevent disturbances by inebriated passengers on board? I don't think so." There are already items on board planes that can be used to harm someone, "whether it's in first class (with) a metal knife or fork, or whether it's a wine glass or a wine bottle that they break and use," Pistole said. The agency is focused on identifying which passengers may have dangerous intentions rather than looking at objects that could be misused, he said. "If we focus only on objects then we're always behind the eight ball," Pistole said. Besides knives, the policy will also allow passengers to include in their carry-on luggage novelty-size baseball bats less than 24 inches (610 millimeters) long, toy plastic bats, billiard cues, ski poles, hockey sticks, lacrosse sticks and two golf clubs. Items like box cutters and razor blades are still prohibited. Knives permitted under the policy must be able to fold up and have blades that are 2.36 inches (60 millimeters) or less in length and are less than a half-inch (127 millimeters) wide. The policy is aimed at allowing passengers to carry pen knives, corkscrews with small blades and other small knives.