The government's new order that all airline passengers put their shoes through X-ray machines won't help screeners find a liquid or gel that can be used as a bomb.
The machines are unable to detect explosives, according to a Homeland Security report on aviation screening recently obtained by The Associated Press.
The Transportation Security Administration ordered the shoe-scanning requirement as it fine-tunes new security procedures.
Those procedures were put in place after British police last week broke up a terrorist plot to assemble and detonate bombs aboard as many as 10 airliners crossing the Atlantic Ocean from Britain to the U.S.
Among the new procedures are a ban on liquids and gels in airline passenger cabins, more hand searches of carryon luggage, and random double screening of passengers at boarding gates.
On Sunday, the TSA made it mandatory for shoes to be run through X-ray machines as passengers go through metal detectors. They were begun in late 2001, after the arrest of Richard Reid aboard a trans-Atlantic flight when he tried to ignite an explosive device hidden in his shoe. The shoe scans have been optional for several years.
In its April 2005 report, "Systems Engineering Study of Civil Aviation Security - Phase I," the Homeland Security Department concluded that images on X-ray machines don't provide the information necessary to detect explosives.
Machines used at most airports to scan hand-held luggage, purses, briefcases and shoes have not been upgraded to detect explosives since the report was issued.
TSA spokeswoman Yolanda Clark said putting shoes on the X-ray machines makes the screening process more efficient and eliminates confusion. "We do not have a specific threat regarding shoes," Clark said. "In an abundance of caution we require all shoes to be removed and X-rayed to mitigate a variety of threats," such as potential weapons.
The Homeland Security report said that "even a 1/4-inch insole of sheet explosive" could create the kind of blast that reportedly brought down Pan Am flight 103, the airliner that blew up over Lockerbie, Scotland, in December 1988, killing 270 people in the air and on the ground.
The Homeland Security report recommends that explosives trace detection, or ETD, be used on the shoes and hands of passengers when the screeners determine they must be checked more thoroughly.
"To help close this gap, the percentage of shoes subjected to explosives inspection should be significantly increased," the report said.
"Within the current state of the art, they afford the only meaningful explosives detection capability at the checkpoint," the report said.
ETD involves a screener using a dry pad on the end of a wand to wipe a surface - baggage, shoes, clothing - and then putting the pad into a machine called an ion mobility spectrometer. The machine can detect tiny particles, or traces, of explosives.
Screeners do use ETD on passengers who have been selected to be screened a second time after going through the checkpoint.
TSA chief Kip Hawley recently acknowledged that the threat from liquid explosives isn't going away - and new security measures designed to thwart the threat may be around for awhile.
The agency is testing equipment to detect liquid explosives at six airports, Hawley said, and he called the technology "very promising."
But, he said, "with a million and a half to 2 million passengers every day, it is not practical to think that we are going to take every bottle and scan it through these liquid scanners."
"We are not going to wait for the perfect device to be deployable," Hawley said in an interview Friday. "We're going to look for a total system to be at the level to make us comfortable."
The agency wants to make better use of a limited resource - airport screeners, whose numbers have been capped by Congress at 45,000. The TSA handles security for 450 commercial airports.
Among the changes the TSA is considering, according to TSA spokeswoman Ellen Howe: