Armed guards can be recognised by an alert, professional terrorist organisation

David Learmount

But sky marshalls should be seen as the final line of defence. Using them is an admission that the airport security has failed. And if the hijacker has managed to get some form of a bomb on board, any badly judged intervention by a sky marshall may cause him to detonate it - that is one of the reasons why it is essential that the sky marshall is well trained and, ideally, unrecognised.

Q: What about locked and secure pilots' cabins?

A: With the advent of suicide hijackers whose aim is using the aircraft as a weapon, specially designed secure cockpit doors are beginning to look like an option that at least requires serious study. Ordinary cockpit doors will not keep a terrorist out - they clearly did not in the 11 September hijacks in the USA, because US airlines have always kept cockpit doors locked.

The doors will have to be armoured, and the pilots are going to have to be provided with all the facilities that they need for the flight, whether long-haul or short, on their side of the door. That would include food and drink as well as a lavatory and rest facilities.

Banning hand luggage of all kinds makes air travel, especially long-haul, just that much more unfriendly

David Learmount

Israeli airline El Al has the tightest security in the world. On its aeroplanes cabin crew have to pass through two armoured doors to get to the flight deck, and they have to lock the first one before the second will open. Studies have to determine whether other airlines face a degree of risk high enough to demand such a big investment, because systems like this are expensive to install, heavy, and also endanger the pilots' ability to escape in an emergency evacuation, and takes up space which could be used for passenger facilities.

Q: What about the benefits of banning hand luggage?

A: Banning hand luggage of all kinds makes air travel, especially long-haul, just that much more unfriendly. You cannot take your book, your toilet bag, your camera, or your briefcase/laptop if you are on a business trip and want to use the airborne time to work. So airlines would want to avoid that. But banning from the cabin all except small bags or a brief case containing these essentials would take a lot of pressure off security staff and make any weaponry more difficult to hide.

Q: Do airport check in staff need better training?

A: Airport staff need to be well trained, well paid and to have some sort of career structure in prospect to enable them to progress in the growing security industry - if that is what they want to do. They also need frequent screen breaks if they are working a scanner, because the greatest problem is keeping their mental concentration and vigilance high. Experience is important, hence the need for motivated operators and a low staff turnover.

Q: What new technology can be used to improve security?

A: Technology is improving all the time. Now the latest scanners are able to recognise and alert the operator to suspicious objects and substances - but the operator's own intelligence is essential to recognise the unfamiliar and be suspicious of it.

That is where the old fashioned human being comes in. Ultimately, hand searches, both of people and baggage, should be conducted whenever there is any doubt. Non-X-ray whole-body scans are being developed, with computer alerting systems.

Finally, personal identity will be able to be checked by hand-scans, retinal scans or other devices now under development. This will make it impossible to use false identity documents.

Q: Is it now inevitable that passengers will now face longer check in times?

A: Things in European airports should not change much when the system shakes down once more, because the infrastructure and staffing for good security systems is basically in place - particularly in the UK where the IRA threat has ensured that standards are high. Despite the need at present for higher levels of vigilance, improved drills and better equipment should keep check-in times under control.

For domestic flights in the USA, however, things are changing dramatically. It is no accident that this weak point was chosen by the 11 September hijackers. Now US travellers are having to forego their fast, cheap system in favour of the European variety. Europeans are already used to long check-ins. Americans, on domestic flights, are not, even though their international flight security is high quality.