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.

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.

Swalwell co-authored a letter to Pistole saying he was "mystified" by his decision, calling it "another example of a questionable TSA policy."

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.