* The sophisticated profiling system designed to screen for high-risk passengers apparently overlooked the hijackers because, based on the history of domestic hijackings, it did not contemplate a suicide mission.
* Commercial aircraft design offered almost no protection from cockpit takeovers. Such attempts, in fact, have been growing more frequent in recent years.
Sometime before 8 a.m. Sept. 11, five men strolled through the airy, spacious lobby of Logan International's Terminal C. As they approached the security checkpoint, they encountered the gentle jingling of the concourse's artistic centerpiece, a Rube Goldberg-like contraption housed in a 6-foot glass cube.
About 50 yards past the sculpture is the security checkpoint leading to Gates C-11 through C-21. Airport officials say the hijackers of United Airlines Flight 175, bound for Los Angeles, passed through here on their way to Gate 19. In the two hours after their 7:58 a.m. departure, they would use weapons believed to have been carried past the security screeners to commandeer the plane and steer it into the south tower of the World Trade Center.
Fourteen other men followed similar paths that morning through security posts at Logan's Terminal B, serving American Airlines, and on airport concourses in Newark, N.J., and at Dulles International near Arlington, Va. Reports differ on whether they checked bags.
Each was likely subjected to the same screening familiar to the 1.6 million passengers who fly U.S. skies every day: a perfunctory X-ray scan of carry-on bags; a walk through a magnetometer portal tuned to detect metallic objects; and very occasionally, a hand search of personal belongings.
Whether the magnetometers could or should have detected the knives or box cutters that investigators believe the hijackers carried on board is unknown. But security professionals do regard the devices, which detect aluminum and other metals containing iron, as far from foolproof. Operators can turn down their sensitivity to speed up passengers' movement through the line.
"The FAA establishes criteria [for the settings], but when the airlines apply pressure, they often turn them down [below FAA specifications]," according to a senior FAA security source.
As for the X-ray equipment used to screen carry-ons, these are easily snookered because they transmit scanning beams vertically. Thus, a knife laid on edge can look as slender as a wire. Most major airports are equipped with more capable scanning systems using computer tomography similar to hospital CAT scanners. These produce three-dimensional images, but are slower and used only on a small percentage of checked bags and an even smaller percentage of carry-ons.
The security companies that operate the screening posts under contract with American and United airlines--Argenbright Holdings Ltd. at the Dulles and Newark terminals, Huntleigh USA at Logan's United terminal and Global Aviation at Logan's American terminal--all say the checkpoints were fully staffed that morning.
"All checkpoints were open, all were operational and fully staffed," said Bill Barber, president of Argenbright, referring to the Newark and Dulles stations.
In any event, many experts agree that the training, expertise and work patterns of staff at airport security checkpoints have been inadequate. Some workers have complained to union officials that rules mandating breaks at least every half-hour to keep them alert are routinely violated.
Mead, the Transportation Department's inspector general, testified Friday that inspectors successfully entered off-limits areas at eight major U.S. airports in 68% of their attempts in 1998 and 1999. They were able to board aircraft 117 times without going through security, often because airport and airline employees didn't close security doors behind them.
FAA enforcement and oversight of the checkpoints also has come under fire. Although agency inspectors regularly run undercover tests of screening stations at airports nationwide, they give screeners the benefit of the doubt.
"For a time, the inspector general was forced to use official FAA test weapons, which were easily recognized by screeners," says Mary Schiavo, a former inspector general of the Department of Transportation and a vocal critic of the FAA. "It was the same stupid Samsonite briefcase every time. They all recognized it--it might as well have had the FAA seal on it."
Weapons and explosives cached inside the bag were designed to be hard to miss: A fake bomb looked like sticks of dynamite attached to an alarm clock by long, curly wires.
"It was like the bomb from Acme Supply on the Road Runner cartoons," Schiavo says. When she suggested taking the fake bomb apart and secreting the pieces, "the screeners said that wasn't fair. There were actually negotiations with the screeners over what kind of items they should be expected to pick up."