TSA chief faces knives-on-planes critics TSA chief John Pistole answers questions at a Homeland Security hearing 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 (CNN) -- As the airline industry piles on against him, the man who ordered knives to be allowed on U.S. commercial airliners defended his decision Thursday on Capitol Hill. "It is the judgment of many security experts worldwide, which I agree with, that a small pocket knife is simply not going to result in the catastrophic failure of an aircraft, and an improvised explosive device will," Transportation Security Administration director John Pistole told lawmakers. 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. After his testimony at the Homeland Security subcommittee hearing, Pistole was expected to face questions from lawmakers who are concerned about traveler safety in a post-9/11 era. Supporters believe the rules should be more passenger-friendly and focus on larger threats. Critics believe even small knives pose too much of a risk for airline crews, arguing that box-cutter knives were used in the 9/11 attacks. 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. Committee member Rep. Eric Swalwell, D-California, is expected to join critics during the hearing. Swalwell co-authored a letter to Pistole saying he was "mystified" by the move, calling Pistole's decision "another example of a questionable TSA policy." So far, the TSA has stood firm. Rep. Michael McCaul, R-Texas, supports the rules change. Commercial aviation must be secure from threats as the highest priority, but Pistole also has a priority to make the TSA both "more passenger-friendly and threat-focused," McCaul said in a recent statement. Former TSA head Kip Hawley -- who agrees with the change -- said sharp objects can no longer bring down aircraft. The TSA made its decision after a threat assessment determined that allowing small knives in cabins would not result in catastrophic damage to aircraft. 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. The rules are to go into effect on April 25. The agency is aligning its knife policy with the International Civil Aviation Organization, which includes the United States and 190 other member nations. The group says each member exercises its own discretion about how to deal with the issue of knives in the cabins. Related: Knives on planes: Who's for it, who's against Under the new rules, 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. Airlines for America, the airline trade association, said Monday that "additional discussion is warranted" before small knives are allowed on planes. Related: Need a tribal spear? 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.