The US is to relax its post-9/11 ban on airline passengers carrying sharp objects, in a move which has alarmed flight attendants and some politicians.
Opponents of the plan insist blades on planes remain a danger
Small scissors and similar items will be allowed from 22 December, says transport security chief Kip Hawley.
Screeners will spend more time checking for explosives under guidelines which will allow for more random searches.
The 9/11 hijackers used small box-cutting knives to seize the planes which they then flew into buildings.
Box cutters and other kinds of knives will remain banned.
The ban on carrying sharp objects on to planes was introduced following the hijackings, in which almost 3,000 people were killed.
Objects such as scissors and razors were placed on a list which meant they could not be carried as hand luggage into the cabin of a plane, and had to be stored in luggage in the hold.
The practice has been followed in other countries since then.
The Transportation Security Administration (TSA) said earlier that it was planning to make better use of its resources.
Mr Hawley, head of the TSA, said that small scissors and tools accounted for about 25% of prohibited items found in passengers' carry-on bags.
Along with small scissors, tools like screwdrivers, wrenches and pliers less than 18cm long will be removed from the prohibited items list.
It was vital, he said, that terrorists should not be able to know with certainty what screening procedures they would encounter at US airports.
"By incorporating unpredictability into our procedures and eliminating low-threat items, we can better focus our efforts on stopping individuals who wish to do us harm," he added.
Air Transport Association spokesman David Castelveter said earlier that he was aware of the plans, and that the industry supported them.
"What we believe, as does the TSA, is that we should be focusing on what poses the greatest risk," he said.
But many flight attendants believe that while such objects could not be used to carry out a 9/11 style hijacking, the items could still be used as weapons to injure other passengers or crew members.
"When weapons are allowed back on board an aircraft, the pilots will be able to land the plane safely but the aisles will be running with blood," said Corey Caldwell, a spokeswoman for the Association of Flight Attendants.
Two US Congressmen, Ed Markey and Joseph Crowley, have said they will oppose relaxing the ban with a bill.
"The Bush administration proposal is just asking the next Mohamed Atta [9/11 hijacker] to move from box-cutters to scissors as the weapon that's used in the passenger cabin of planes," Mr Markey said.