By Ryan Dilley BBC News Online

'You know a lot more about planes than guns'

"You know a lot more about planes than guns. That's a Smith and Wesson .45. If you fire at this close range, the bullet will pass through me and the fuselage like a blowtorch through butter. The cabin will depressurise and we'll both be sucked into outer space together."

This lesson on the dangers of discharging firearms on high-flying aircraft was delivered not by those training the UK's soon-to-be deployed sky marshals, but by none other than James Bond in Goldfinger (1964).

007's warning to pilot Pussy Galore that waving a pistol around the cabin of a jet in flight would end in tears has largely shaped the popular debate about what actually happens when bullets breach an aeroplane's fuselage.

Truth behind the fiction

As with most works of fiction, the Goldfinger explanation of explosive decompression is misleading, but contains a worrying grain of truth.

A slug from a .45 might well pass through a human body and the metal airframe "like a blowtorch through butter", but the small hole in the fuselage would only slowly leak air from the high pressure environment inside the cabin into the lower pressure atmosphere outside.

But even this kind of decompression could rob passengers and crew of oxygen. In 1998, an undramatic loss of cabin pressure through a cracked door caused the captain of a UK-based airliner to pass out when he failed to fit his emergency oxygen mask in time.

Goldfinger mixes fiction with some fact

In the airborne climax of Goldfinger, Bond wrestles with the film's eponymous baddie, eventually shooting out a window. Despite his girth, Auric Goldfinger is indeed agonisingly blown through the hole and into oblivion.

Just as Gwyneth Dunwoody, the chairman of the House of Commons transport select committee, said of government plans to place armed guards on airliners: "People with guns and aircraft do not mix."

Frank Taylor, a senior lecturer in air safety, says a bullet destroying an aircraft window in real life would have dire consequences for nearby passengers, as dramatised in Goldfinger.

As air rushes out to equalise the "pressure differential" between inside and out, it can reach the speed of sound and pick up objects and people.

Ready to fly

"It's not all fiction. If an airliner's window was shattered, the person sitting beside it would either go out the hole or plug it - which would not be comfortable."

Such a prospect has not deterred Transport Secretary Alistair Darling from pushing ahead with plans to put armed undercover agents on commercial flights with orders to tackle those endangering the aircraft.

Mr Darling told a Sunday newspaper that following a recruitment and training programme - which began in the wake of the 11 September hijackings - "the facility is there".

Taking on an armed opponent at 30,000ft is a tricky task

The UK's Department of Transport is examining "less than lethal" alternatives to bullets, but these have yet even to prove themselves in normal policing, let alone against determined hijackers. So how safe can passengers feel about sky marshals resorting to gunplay to end a hijacking?

The best defence against stray bullets, apart from not firing in the first place, is to ensure the projectiles enter their intended target and stay there.

Air marshals deployed in the US - where armed guards were first sent into the skies by President Nixon - use hollow point bullets. These expand on hitting the body - giving up much of their energy and slowing down - thus reducing the chances of what is chillingly called "over penetration".

However, the UK's armed police officers - from whose ranks Mr Darling's sky marshals are reportedly drawn - do not have an unblemished record of marksmanship. More than half of the bullets they fire in the line of duty miss their target.

Wide of the mark

The sky marshals will undoubtedly have received specialist training, but would this accuracy rate be significantly improved in the crowded confines of a moving airliner mid-hijack?

The other option is to minimise the damage inflicted by errant bullets, not only to prevent decompressions but also to safeguard the mechanical and electronic systems of the aircraft which run through the cabin.

So-called frangible rounds have found favour with air marshals in some countries. These bullets are not made of solid lead, but instead metal fragments which devastate soft targets but disintegrate upon striking a less yielding surface.

Is it better to tackle hijackers here or in the air?

Such a careful selection of ammunition would not save innocent passengers nor, vitally, pilots caught in the firing line. Frangible rounds would also limit the effectiveness of air marshals tackling hijackers wearing body armour or those who had taken cover.

Airlines and security experts have expressed reservations about the value of air marshals, arguing that the authorities have already failed in their duty if hijackers pass the checks conducted before take-off.

Industry observers in the US also suggest that airlines have another grumble about the greatly increased number of air marshals post-11 September. The seats the agents tend to favour - which offer them the best firing positions to protect the cockpit - happen to be the comfy and lucrative ones in first class.

Some of your comments so far:

While the fictional Commander Bond may know his ballistics, he doesn't know much about physics. He and the luminously beautiful Ms Galore would have been blown out into space, not sucked out.
Saul Hazan, UK

Why not use another James Bond "special," knock-out gas? When the captain realises he is being hijacked, he would fit his oxygen mask and then release the gas into the passenger cabin.
Alex Hunter, UK

I would not fly with an armed guard on board. I think it is more a case of guns and people do not mix, rather than guns and planes. Decreasing my chances of a fairly good seat would seriously upset me as well. The air marshal should be assigned a small pull-down seat attached to the cockpit door for take off and should then constantly patrol the aisles with gun poised to bring down any potential terrorist.
Brian T, UK

In a hijack situation, how will other passengers know which armed person is a hijacker and which is the sky marshal, and what would stop a hijacker masquerading as a marshal? What could be done to prevent a marshall losing possesion of his/her weapon and ending up in the hands of a hijacker?
Dan Day, UK

I would much rather have an armed air marshall shooting holes in the side of the plane than a group of terrorists flying it into the side of a building. Just because taking on terrorists in the sky is dangerous work, does not mean that the risk isn't worth it.
Dave, Cheshire, UK/Canada

As a longhaul pilot for a leading worldwide airline I am totally against this publicity driven move. The key to security in the air is to prevent any risk element boarding an aircraft in the first place. Travellers should expect and tollerate watertight security, and Governments should not shy away from tackling the problem because it's expensive. To introduce a lethal weapon into a sterile environment compounds a problem that should not be allowed to exist in the first place.
Jon Truscott, UK

An aircraft cabin already leaks more than the equivalent of several tens of bullet holes, so one extra is not going to make any difference. Its pressurisation depends merely on pumping in more than leaks out. As far as armed guards are concerned, they can take a tip from the Israelis who, I have heard, carry reduced charge 0.22 pistols. A well-aimed shot can stop a man, but it will not penetrate the cabin wall, particularly with all its lining and insulation.
Steven Groeneveld, Italy

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