The man who boarded a Paris-to-Miami flight with explosives allegedly hidden in his shoe may have exploited a loophole that would make it easier for terrorists to smuggle bombs on their bodies than in baggage, a security expert said Sunday.

While high-tech screening machines can detect explosives inside checked and hand-carried luggage, the devices that check passengers are not yet sophisticated enough to find some bomb material, said Chris Yates, aviation security editor at Jane's Transport.

"The received wisdom has always been that if someone were going to trigger a bomb on an airplane it would typically be concealed either in hand or hold luggage, so the aviation industry for a lot of years has gone down the line of deploying equipment to deal with that threat," Yates said.

"It's only fairly recently that we've come across this phenomenon of suicide bombers, suicide hijackers, and the industry is not geared up to deal with those types of people," he said.

A passenger on American Airlines Flight 63 from Charles de Gaulle airport to Miami tried to ignite a material in his sneakers which The Associated Press learned had tested positive for explosives. The plane was diverted to Boston on Saturday.

French police identified the passenger as a Sri Lankan, 28-year-old Tariq Raja, and said he was traveling on a British passport under the name Richard Colvin Reid. In London, Scotland Yard said they believed he was a British national but were still trying to confirm that.

Authorities said a flight attendant on the plane intervened when the man tried to light a fuse protruding from his shoe, and passengers and crew subdued the man.

Laura White, a spokeswoman for the Massachusetts Port Authority, said the material inside the heel of one of Raja's shoes was "consistent with" the plastic explosive C-4, which was used in the deadly October 2000 bombing of the USS Cole in Yemen. Experts say it would have been difficult hard to set off the material.

Mike Yardley, a terrorism expert and former British Army officer, said the incident was a reminder of how vulnerable travelers can be, even after the boost in security in response to the Sept. 11 terror attacks.

"This is another example of how the low-tech approach has defeated airport security systems," he said. "It draws chilling comparisons with Sept. 11, where the terrorists managed to gain control of the planes with something as low-tech as knives."

Yates said there are handheld devices which can detect even small amounts of explosive, but they are relatively new and not in wide use.

About a dozen dogs trained to detect explosives are stationed at Charles de Gaulle airport. However, an air transportation expert told the AP that it is "practically impossible" to have enough dogs to check the tens of thousands of passengers who board flights daily.

French police are investigating how the man was allowed to board the flight with a questionable passport and almost no luggage, just one day after he was turned away from another flight for questioning because he had raise police suspicions.

In Britain, all checked bags must be screened for explosives with X-ray or CT machines similar to medical CAT scanners. America's new aviation security bill requires U.S. airports to do the same by the end of 2002.

France also plans to screen all checked bags for explosives by the end of 2002.

Earlier this month, authorities in Boston revealed passport-authenticating scanners that will be tested at Logan International Airport. The machines already are being used at London's Heathrow and Gatwick airports.

The "BorderGuard" devices scan documents and photos to detect whether a passport or license's laminate has been altered or a name retyped. They also compare the information to federal lists of suspected terrorists, and create a database, photographs included, that law enforcement agencies can access.