Airlines and airports are still tightening every aspect of security in the aftermath of 11 September, although not all measures are fully in place.
British Airways introduced a £2.50 surcharge to pay for an initial £1.1m in extra safeguards after the attacks. It has more hand-baggage and passenger searches at the boarding gate as well as those at the departure halls, cockpit doors are kept locked and being armour-plated, and sharp objects such as tweezers or needles are banned from hand luggage.
The airline is now considering the more dramatic measures of arming cabin crew with stun guns and using closed circuit television so all sections of the plane can be continuously monitored.
A spokeswoman said CCTV had been successfully tested for cargo areas and could be extended to the passenger cabin. BA was studying the benefits of issuing Taser stun guns, although it would need legislation to arm the crews with them.
Virgin Atlantic has adopted similar measures to BA, and both are working with the British Airports Authority to test eye-scans as a means of detecting people who are using false passports. The trials will start at Heathrow next year and will involve about 2,000 passengers who regularly fly with the two airlines.
A BAA spokeswoman said the extra searches and tighter restrictions on hand luggage had been introduced at all airports. An extra 200 security guards had been recruited at Heathrow and a similar number are being hired for Gatwick. An extra £10m had been spent on security since 11 September, which helped to pay for a heavier police presence, including dogs trained to find explosives.
In the US, United Airlines has Taser guns in cockpits on its 500 planes. American Airlines has a system that ensures every piece of baggage is matched to a passenger. The Federal Aviation Authority has recruited thousands of plainclothes security guards as marshals on all US commercial flights, and has taken over the employment of 28,000 airport baggage screeners, who had worked for airlines.
The Israeli airline El Al, with a reputation as the world's safest operator, never discusses its precautions, but it certainly has sky marshals on all flights and subjects passengers and their luggage to stringent security checks. An Israeli airline security expert said El Al would probably have spotted the shoe bomber because his Middle Eastern appearance did not match his British passport.
An Israeli company, MS-Tech, has developed a device, known as Mini-Nose, which can detect explosive particles at a distance. The device, weighing barely 300 grams, was demonstrated to the Pentagon in August, and the company expects US approval within a year.