Beginning Friday, airline passengers will go through double screening to make sure they're not carrying liquids onto planes, the head of the airline industry's largest trade group said.
Passengers and their carry-on luggage will be checked not only at the main security checkpoint, but also a second time at the boarding gate. The stepped-up screening in response to a new terrorist threat began Thursday at 25 airports where planes leave for Britain.
"It's going to spread across the whole system tomorrow," James May, president of the Air Transport Association, said Thursday.
The response to the terrorist threat produced long lines at airports Thursday as security officials scrambled to put new measures in place and passengers faced perplexing new restrictions - including the ban on carrying liquids onto aircraft.
Intelligence had indicated the terror plot unfolding in Britain involved using benign liquids that could be mixed inside an airplane cabin to make an explosive.
While plots to blow up airliners using liquid explosives are nothing new - such an attempt was foiled more than a decade ago - the government has been slow to upgrade its security equipment at airport checkpoints so that it can detect explosives on passengers.
Transportation Security Administration chief Kip Hawley said the need to tighten security came as a surprise and the changes were difficult to implement.
"It normally takes us about four weeks to roll out a change at a security checkpoint, and this one came about in a little bit more than four hours in the middle of last night," Hawley said.
Duane Woerth, president of the Air Line Pilots Association, said the government was overreacting. "They paralyzed the system with the hassle factor again," Woerth said.
During the first few hours of the alert, the TSA was taking toiletries away from flight crews, he said. "Then they said, 'This is stupid. We're taking toothpaste away from the guy who's going to fly the plane.' It didn't take them long to back down."
But Frank Cilluffo, director of the Homeland Security Policy Institute at George Washington University, said it makes sense to insert "uncertainty and randomness into the system so we can't let the adversary game the system."
Still, he said, coordination among agencies and the industry remains a problem.
Denis Breslin, spokesman for the American Airlines pilots union, faulted nagging communication shortcomings among intelligence, law enforcement and homeland security agencies.
"There's a whole lot of people making rules up right now, and until they get it all sorted out, every passenger is going to have to go through the nightmarish procedures that they're putting together right now," said Breslin.
David Mackett, a pilot who heads the Airline Pilots Security Alliance, said flight crews are treated as part of the problem.
"We're not happy that every time there's a threat we find out from the media, and that there's almost a complete vacuum of information when it comes to the air crews," Mackett said.
It was after the Sept. 11, 2001, attacks that box cutters and other sharp objects were banned, bulletproof cockpit doors installed and air marshals rushed into service.
And it was after Richard Reid, the confessed shoe bomber, tried to blow up a trans-Atlantic flight in December 2001 that security officials made passengers remove their shoes. Lighters were later banned from passenger cabins.
Members of Congress have for several years criticized the TSA for using 1970s-era X-ray technology to screen carry-on bags at security checkpoints.
Rafi Ron, former head of security at Israel's Ben Gurion Airport and now a security consultant in Washington, said part of the problem is that terrorists always try to exploit new vulnerabilities.
"Weapons and explosives are various and you can expect new types of weapons as well as tactics," Ron said.