A passenger is scanned with a wand at an airport check-in Photo: GETTY  Americans are going through a collective spasm of frustration at the failure of the country's security apparatus to identify that Umar Farouk Abdulmutallab was a terrorist, and prevent him from boarding NorthWest Airlines flight 253 from Amsterdam to Detroit. I am currently in the US, and the media here are full of security experts screaming that "Nothing has been learnt since 9/11 – the billions spent on airline security have not made flying significantly safer!"  It is certainly true that what stopped Abdulmutallab from murdering hundreds of people was nothing to do with the additional airline security measures America has imposed since 9/11. It was a combination of his own ineptitude and the bravery of his fellow passengers, who leapt on him the moment they perceived he was attempting to set fire to himself.  That, however, does not mean that the whole effort to improve airline security has been a waste of time and money. US intelligence picked up on conversation between al-Qaeda operatives in Yemen as they said they were going to use a "Nigerian" for a terrorist attack. Adbulmutallab is a Nigerian – but that would not count for much, since Nigerians number well over 150 million, had it not been for the fact that his father warned the US embassy in Nigeria that his son had adopted a dangerously extreme form of fundamentalist Islam. Officials in Washington put Adbulmutallab's name on a database of 550,000 people who might be connected to terrorism in some way.  The problem was that they stopped there: they didn't put him on the no-fly list (which contains 4,000 names), or even on the list of 14,000 people who have to undergo additional screening before they are allowed to fly to America. If the system had worked properly, they would have taken at least one of those steps.  Still, I have a smidgin of sympathy for the security officials being lambasted for their incompetence. Yes, it's true that had they connected and properly evaluated each piece of information they had, they would have stopped Abdulmutallab from flying. But it is difficult for outsiders to appreciate the deluge of data that those guys have to deal with. Thousands, indeed millions, of pieces of information arrive every day, and the vast majority are false, misleading or useless. And when officials act on information that turns out to be wrong, they are excoriated for persecuting innocent people, and even for "doing al-Qaeda's work" by "alienating ordinary law-abiding Muslims" through their viciously oppressive intervention. Understandably, it acts as a disincentive to put everyone who might in some way be connected to terrorism straight on to the no-fly list.  One problem created by collecting vast amounts of information, as the US's network of spy satellites allows it to do, is that vast numbers of extremely able people are needed to analyse it – and not very many extremely able people want to be employed in that job.  After almost every act of terrorism, the subsequent investigation reveals information which, had its significance been realised, would have allowed the authorities to stop the bombing. One of the most poignant examples is the Omagh atrocity. In that case, GCHQ listened to a conversation between the Omagh bombers as they drove the car that contained the bomb to Omagh. The security officials did not, of course, realise what they were listening to. But when you know what happened, it becomes very difficult to appreciate why they failed to work it out.  "Human error" – blunders, oversights, laziness – on the part of security officials will always explain why terrorists get through security measures, just as human error is what causes most car accidents and most plane crashes. That will be true no matter how sophisticated those security measures become. It's no reason to think that the whole paraphernalia of airport security is a waste of time. But it is a reminder that if you want to be 100 per cent safe, you should stay at home.
As Umar Farouk Abdulmutallab demonstrated in Detroit, airline security is only    as strong as the people who run it.