Story highlights TSA administrator: "I think the decision is solid and it stands"

Congresswoman: "You need to stop this now"

New rules would allow knives with blades up to 2.36 inches long on airlines

Groups for airlines, screeners, air marshals, flight attendants and pilots have concerns

The nation's aviation security chief on Thursday defended his recent decision to again permit knives aboard commercial flights, despite concerns from major airlines and their flight crews, and sharp criticism from some members of Congress.

John Pistole, administrator of the Transportation Security Administration (TSA), told a House Homeland Security subcommittee that his decision would stand and would be carried out next month as planned.

He said small knives no longer pose a threat to aircraft security, which now emphasizes bomb detection.

"A small pocket knife is simply not going to result in the catastrophic failure of an aircraft and an improvised explosive device will," he said. "And we know, from internal covert testing, searching for these items, which will not blow up an aircraft, can distract our officers from focusing on the components of an improvised explosive device."

Small knives were banned along with a host of other undersized sharp objects like nail clippers, screwdrivers and cosmetic scissors, following the 9/11 al Qaeda hijack attacks on the United States.

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There has been a gradual easing of those prohibitions in recent years as planes hardened onboard security and the potential threats shifted away from hijackings and more toward attempts by terrorists to bring down planes with bombs.

Still, Pistole's decision has roiled the industry. The major carriers have as a group raised concerns about the move with three - Delta, American, and US Airways coming out in opposition.

Pistole's supporters believe the rules should be more passenger-friendly and focus on bombs and other threats that can be hard to detect and be smuggled aboard the passenger cabin or in cargo.

But critics contend that even small pocket and other knives still pose too great a safety and security risk for airline crews, reminding that the 9/11 hijackers used box cutters to take control of four jetliners.

Pistole stood firm as he faced questions and criticism from lawmakers.

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

Rep. Eric Swalwell, D-California, criticized the logic behind the move, arguing that threats posed by bombs do not mean knives aren't dangerous.

"Just because this is a new threat does not mean that old threats don't still exist," he said.

Rep. Sheila Jackson Lee, D-Texas, said Pistole needed to change course on the rule change -- fast.

"You need to stop this now," she said. "These cause bleeding. These cause injury. These can cause a terrible tragedy. And I don't want to take it to the next length. It can possibly cause someone to lose their life."

Other lawmakers said they supported Pistole and praised his efforts in leading the agency.

"Why should the federal government devote taxpayer dollars to low-risk people, places, or things?" said Rep. Richard Hudson, R-North Carolina, the subcommittee's chairman.

In the nine days since the TSA opened a can of worms by announcing it would ease the ban on small knives in airline cabins, the list of groups concerned or opposed to the idea has grown to include airlines, airport screeners, federal air marshals, flight attendants and pilots.

The surge in recent criticism from so many groups drew the attention of Rep. Cedric Richmond, D-Louisiana.

"I don't question your judgment, because you do what you do, and we have to trust that you're making the right decisions," Richmond said.

But he said he questioned the process Pistole had used, arguing that he hadn't involved enough stakeholders from the airline industry.

"I'm not asking you to defer to them, but a lot of the time it helps if they're at the table when you're making a decision so that they have the information that you have," he said.

Pistole said he met with flight attendants on Wednesday, but conceded that he could have done a better job of bringing them into the process earlier.

Under the new rules, which go into effect April 25, knives with blades that are 2.36 inches (6 centimeters) or shorter and less than a half-inch wide will be allowed in airline cabins so long as the blade is not fixed or does not lock into place.

The rules also allow passengers to carry up to two golf clubs, certain toy bats or other sports sticks -- such as ski poles, hockey sticks, lacrosse sticks and pool cues -- aboard in carry-on luggage.

The TSA has said it's aligning its policy with international rules.

But after consulting with Federal Air Marshal Service leaders, the agency opted to continue excluding knives that most closely resemble weapons, specifically knives with blades that lock in place, or have molded hand grips.

Box cutters and razor blades also would remain on the prohibited items list.

Airlines for America, the trade association representing the major U.S. airlines, said Monday that "additional discussion is warranted" before small knives are allowed on planes. Three of the nation's five biggest carriers, Delta, American and US Airways, have spoken out against the policy.

Many critics of the new rules contend that in addition to adding an unnecessary threat to the safety of airline crews and passengers, the changes won't make a difference in the TSA's ability to concentrate on other threats.

Knives are probably the most common items surrendered by passengers at screening points, aside from liquids.

Travelers surrender about 35 knives at Baltimore-Washington International Airport on an average day and about 47 per day at Los Angeles International Airport, officials say.

"Today, we find on average of four guns at checkpoints, but we also find about 2,000 of these small pocket knives every day," Pistole said on Thursday.

"On average that takes two to three minutes for the pocket knife to be identified, for that bag to be pulled, for that bag to be opened, for the knife to be found," he added.

That's valuable time, he said, noting that other more dangerous items could slip by security screeners.

Questioned by reporters, White House spokesman Jay Carney said he did not think President Barack Obama had a response to the issue.

"I'm sure that the TSA has been asked this question and explained their thinking in making decisions like this; DHS as well, I assume," Carney said of the TSA's parent agency, the Homeland Security Department.

"My understanding as a layman, as an observer, not as somebody who has worked the policy process, is that this has to do with an assessment of where the most likely threats are," Carney said.