Tiny bomb 'still threat to plane'

Passengers and crew overpowered the suspect

Even explosives small enough to be hidden in a passenger's shoe can endanger an aircraft, experts say.

An investigation has been launched into how a man boarded an American Airlines Boeing 767 from Paris to Miami with explosives in the heels of his shoes.

This is another example of how the low-tech approach has defeated airport security systems

Terrorism expert Mike Yardley

After the suicide attacks of 11 September, airports have concentrated on searching passengers for sharp objects and scanning luggage for guns or explosives.

But the discovery of a passenger with explosives hidden in his shoes has added a new dimension to aircraft security.

Senator Richard Shelby, a senior member of the US Senate Intelligence Committee, told CBS television: "It would be my judgment... that this man was trying to blow himself up and blow the plane up and we are very fortunate it didn't happen."

The man - carrying a British passport in the name of Richard Reid - was overpowered by crew and passengers before the devices could be detonated and the plane was diverted to Boston.

Laura White, a spokeswoman for Massachusetts Airport Authority, said the material in the shoes was enough to cause considerable damage to the aircraft.

Difficult to detect

She said it was consistent with the plastic explosive C-4.

However, news agency AFP quoted a source close to French police saying the substance was the high explosive pentrite.

Aviation security expert Brian Jenkins, who served on the White House Commission on Aviation Safety and Security, told ABC television: "Even a small explosion on a plane at altitude in a pressurised cabin can be extraordinarily dangerous."

C-4 - a clay-like substance - is used for industrial and military purposes and is believed to have been the explosive used in the attack on the USS Cole in Yemen in October 2000 which killed 17 people.

A small bomb destroyed this plane in Thailand

Pentrite was used in the bombing of a French DC-10 over the Tenere Desert in Niger in 1989. The attack was blamed on Libyan agents.

A bomb made from about 4oz (110g) of C-4 blew out the roof of a Thai Airways jet in March, killing one person and injuring several others.

Mike Yardley, a terrorism expert and former British Army officer, said the incident highlighted how vulnerable travellers were, even with the increased security following 11 September.

'Chilling comparisons'

"This is another example of how the low-tech approach has defeated airport security systems," he said.

"It draws chilling comparisons with 11 September, where the terrorists managed to gain control of the planes with something as low-tech as knives."

Plastic explosives like C-4 cannot be detected by regular scanning devices used in airports, transportation experts say, only by sniffer dogs.

However, Mr Yates said there were handheld devices which could detect even small amounts of explosive, but they were new and not widely available.