(AP Photo/Elaine Thompson, File)

WASHINGTON -- The head of the Transportation Security Administration told lawmakers Thursday he stands by his plan to allow passengers to carry small knives onto planes despite a growing backlash against the proposal.

It's unlikely in these days of hardened cockpit doors and other preventative measures that the small folding knives could be used by terrorists to take over a plane, TSA Administrator John Pistole told a hearing of the House Homeland Security Committee.

On the other hand, searching for the knives on passengers or in their carry-on bags is time consuming, Pistole said. TSA screeners confiscate about 2,000 such knives every day, with each incident chewing up about two to three minutes, he said.

"I think the decision is solid and it stands and we plan to move forward," Pistole said.

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The policy, which goes into effect April 25, has sparked strong opposition from flight attendants, federal air marshals, some pilot unions, and even aviation insurers. In the hands of the wrong passengers, the knives can be used to harm flight attendants and other passengers, critics say.

Several airline CEOs have also expressed qualms. Delta Air Lines chief executive Richard Anderson said in a letter to Pistole last week that he shares the "legitimate concerns" of the airline's flight attendants. US Airways chief Doug Parker asked the TSA administrator to reconsider his position.

Several members of the House committee also urged Pistole to drop the proposal, warning that if he doesn't, Congress may take steps to block the policy change.

Since the Sept. 11, 2001, terrorist attacks there have been no incidents in which terrorists have successfully used sharp objects to take over a plane, which suggests the current policy of keeping even small knives off planes is working, committee members said.

"How does allowing sharp objects on board now accomplish maintaining the goal of having zero planes taken over?" asked Rep. Eric Swalwell, D-Calif. "I'm asking why now, and why do we want to go back?"

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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.

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There has been a gradual easing of some of the security measures applied to airline passengers after 9/11. In 2005, the TSA changed its policies to allow passengers to carry on airplanes small scissors, knitting needles, tweezers, nail clippers and up to four books of matches. And in September 2011, the TSA no longer required children 12 years old and under to remove their shoes at airport checkpoints. The agency recently issued new guidelines for travelers 75 and older so they can avoid removing shoes and light jackets when they go through airport security checkpoints.

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