Comment As the smoke clears following the case of Umar Farouk Abdul Mutallab, the failed Christmas Day "underpants bomber" of Northwest Airlines Flight 253 fame, there are just three simple points for us Westerners to take away.

First: It is completely impossible to prevent terrorists from attacking airliners.

Second: This does not matter. There is no need for greater efforts on security.

Third: A terrorist set fire to his own trousers, suffering eyewateringly painful burns to what Australian cricket commentators sometimes refer to as the "groinal area", and nobody seems to be laughing. What's wrong with us?

We'll look at the first part to begin with.

In order to destroy an airliner and kill everyone on board, one needs to do a certain amount of damage to it: a lot if it is on the ground without much fuel in it, not so much if it is fuelled up, less yet if it is flying at low altitude, and least of all if it is flying high up.

Formerly there was the option of gaining access to the flight deck - perhaps using the aircraft as a weapon, as on 9/11, perhaps to carry out a hostage strategy - but those days are gone. The 9/11 hijackers have seen to it that the best and most effective ways for terrorists to employ airliners are no longer open to them. Pilots will never open flight deck doors again, no matter the threat to hostages in the cabin; passengers will not permit themselves to be dominated; armed sky marshals are back. If all these fail, following the bloodbath at Ground Zero fighter pilots will not hesitate to shoot.

So the damage must nowadays be done by other means than crashing, most practically by detonating a charge of high explosives on the plane while in flight. This doesn't need to be too big, especially if the jet is at cruising height so that the explosive effects will be enhanced by depressurisation. This is why airliners are a favourite target: because a fairly small amount of explosive can potentially kill a large number of people in one go, which is not the case under most circumstances.

It is an unfortunate and pretty much unavoidable fact that the necessary amount of explosives can easily be carried through any current or likely-future airport security regime, short of universal strip + cavity searches and a total ban on carry-on luggage.

Let's consider, for instance, a future security check involving backscatter X-ray-through-clothes perv scans - much more effective than millimetre wave - and X-raying of carry-on bags as is already normal. There are several ways to beat this.

Firstly, detonators and firing devices can be disguised within permitted electronic equipment such that they will pass through X-raying without trouble. An AA battery casing full of hexamethylenetriperoxidediamine (HMTD) - or some similar sensitive primary - with a flashbulb filament in it is almost impossible for an X-ray operator to pick out from among others, and can be triggered by the flash circuits of any camera.

The difficult bit is the main charge, which needs to be a decent weight and volume of acceptably stable high explosive. But it's not that difficult. Here are just a few ideas:

Several terrorists - only one of whom would need to go aboard the target flight - could carry permissible amounts of liquid explosives through security, combining them later in the air-side lavatories.

Readily available plastic explosives can be rolled out into flat, uniform sheets - they can actually be bought in this form, for instance under the name "Sheetex" - and cut to shape with ease. Such sheets can easily be inserted into luggage, where they won't look noticeably different from normal cardboard or plastic structure, partitions etc under X-ray if they aren't too thick. There are many other ploys along these lines; a sensible and well-resourced terror group could probably buy an X-ray machine and develop a bag containing a charge, detonator and firing circuit which looked entirely legit under scan.

Reasonable amounts of main charge can be carried stuffed into body cavities, undetectable by any body-scan. They would need to be removed before use in order to escape the pronounced dampening effect of the human body, and probably combined with other such payloads to get a bang sure to do the job, but again teamwork and lavatories will see to this.

There's more scope still for the use of checked baggage. US and many other airports nowadays X-ray this, but there are airports which don't. You can easily find out, as a terrorist organisation, routes on which a checked bag won't be X-rayed by packing some unexposed film and making some flights. Once you have identified an airport that doesn't X-ray checked bags, simply put a large time- or barometrically-triggered bomb into a suitcase and have your suicide operative check it before boarding.

The list goes on - and on. Any reasonably competent terrorist organisation, with access to funds, capable technical experts and a small number of operatives able to move about the world freely can blow up airliners in flight. You wouldn't even necessarily need suicide volunteers to carry the bombs, if you were cunning: dupes might be convinced that they were smuggling drugs, money or other contraband, or IRA-style "proxy bombers" could be forced to do your bidding by seizing and threatening their families.